tag:theconversation.com,2011:/fr/topics/hubble-25-16280/articlesHubble 25 – The Conversation2015-12-20T19:55:02Ztag:theconversation.com,2011:article/522092015-12-20T19:55:02Z2015-12-20T19:55:02Z2015, the year that was: Science + Technology<figure><img src="https://images.theconversation.com/files/105373/original/image-20151211-8335-1tq3brf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">2015 saw us complete our exploration of all nine planets (including dwarf planet Pluto) in our solar system.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>This year came and went almost as fast as NASA’s <a href="https://theconversation.com/au/topics/new-horizons">New Horizons</a> probe zipped past the distant dwarf planet, Pluto. Yet New Horizons managed to pack a lot into its <a href="https://theconversation.com/beyond-pluto-new-horizons-mission-is-not-over-yet-44520">flyby</a>, revealing <a href="https://theconversation.com/stunning-crystal-clear-images-of-pluto-but-what-do-they-mean-47517">astounding images</a> of Pluto that show it to be far from a static icy world. </p>
<p>And its mission isn’t over yet; New Horizons will now venture deep into the outer <a href="https://theconversation.com/beyond-pluto-new-horizons-mission-is-not-over-yet-44520">reaches of the solar system</a>, probing the expanse of the Kuiper belt and shedding light on this ancient and hitherto unexplored region of space.</p>
<p>Fuelling planet fever (dwarf or otherwise) was also one of the most scientifically accurate – and science-celebrating – films to emerge from Hollywood in recent times: <a href="https://theconversation.com/the-martian-review-science-fiction-that-respects-science-fact-48373">The Martian</a>.</p>
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<a href="https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105374/original/image-20151211-8297-166ktng.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Being suck on Mars has never been so fun.</span>
<span class="attribution"><span class="source">20th Century Fox</span></span>
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</figure>
<h2>Eye in the sky</h2>
<p>Speaking of space, this year was the 25th anniversary of the Hubble Space Telescope, which has proven to be one of the most enduringly popular and <a href="https://theconversation.com/why-the-hubble-space-telescope-has-been-such-a-stellar-success-40312">most successful</a> scientific projects in history. </p>
<p>Besides its triumphs of discovery, Hubble has also generated a startling array of wonderous images of our universe. Best of all is when those images are both <a href="https://theconversation.com/hubble-in-pictures-astronomers-top-picks-40435">beautiful and richly informative</a>.</p>
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<a href="https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105375/original/image-20151211-8329-183atk1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Happy 25th Hubble!</span>
<span class="attribution"><span class="source">NASA</span></span>
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<p>And speaking of anniversaries, it was one hundred years ago that Albert Einstein altered the face of physics by publishing his <a href="https://theconversation.com/au/topics/general-relativity-centenary">general theory of relativity</a>. It’s hard to overstate the significance of this revelation about the nature of space and time. </p>
<p>It’s also difficult to fathom how <a href="https://theconversation.com/without-einstein-it-would-have-taken-decades-longer-to-understand-gravity-50517">just one man</a> was able to come up with a theory of such breathtaking accuracy, and such <a href="https://theconversation.com/the-art-and-beauty-of-general-relativity-51042">profound beauty</a>.</p>
<h2>Smart batteries, smart houses</h2>
<p>More down to earth were significant developments in battery technology. While we might not think of batteries as the glamorous vanguard of technology, they underpin the mobile technology we’ve become accustomed to, and they can also potentially transform the way we <a href="https://theconversation.com/tomorrows-battery-technologies-that-could-power-your-home-41614">generate, store and consume energy</a>.</p>
<p>At least, that’s what Tesla Motors CEO Elon Musk is banking on with the announcement of the company’s home battery offering, <a href="https://theconversation.com/the-winners-and-losers-in-teslas-battery-plan-for-the-home-41151">Powerwall</a>. </p>
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<a href="https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=200&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=200&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=200&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=251&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=251&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105376/original/image-20151211-8291-19mdkci.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=251&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Tesla Powerwall could make solar power work all day and all night.</span>
<span class="attribution"><span class="source">Tesla Motors</span></span>
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</figure>
<p>Another technology that promises (or threatens, depending on your perspective) to transform the world is <a href="https://theconversation.com/your-questions-answered-on-artificial-intelligence-49645">artificial intelligence, robotics and automation</a> more generally.</p>
<p>The first wave is likely to be in the form of <a href="https://theconversation.com/where-we-are-on-the-road-to-driverless-cars-50079">driverless cars</a>, which will not only be safer and more efficient than those driven by hairless primates, but also could change the way we think of things like <a href="https://theconversation.com/driverless-cars-will-change-the-way-we-think-of-car-ownership-50125">car ownership</a>. </p>
<p>But then, what will happen to all those people who currently make a living from driving? Like many, they may <a href="https://theconversation.com/could-a-robot-do-your-job-short-answer-yes-39569">lose their jobs</a> to increasing automation. We may need to <a href="https://theconversation.com/we-need-new-jobs-as-the-machines-do-more-of-our-work-38600">create new jobs</a> in the wake of the robot invasion, but even that might not be enough.</p>
<p>More menacing is the prospect of lethal autonomous weapon systems, colloquially called “killer robots”. There are already defensive weapon systems that can operate autonomously, but this year saw a call by many of the leading AI and robotics researchers to <a href="https://theconversation.com/open-letter-we-must-stop-killer-robots-before-they-are-built-44577">ban offensive autonomous weapons</a>. </p>
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<img alt="" src="https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=283&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=283&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=283&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=356&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=356&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105378/original/image-20151211-31729-6ee31w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=356&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">The robots are coming, although they probably won’t look like this.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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</figure>
<h2>Digital scapes</h2>
<p>This is not to say we don’t already have challenges to face in the digital world. Cybercrime is still a scourge, with it become more <a href="https://theconversation.com/how-cybercrime-has-changed-over-the-past-5-years-it-hasnt-got-any-better-47027">professional and businesslike</a> over the year.</p>
<p>Hackers have a growing <a href="https://theconversation.com/hackers-kit-bag-the-tools-that-terrorise-the-internet-37715">range of tools</a> at their disposal to steal your identity, extort you, pilfer your information or even penetrate business or <a href="https://theconversation.com/cyber-breach-at-the-bureau-of-meteorology-the-who-what-and-how-of-the-hack-51670">government</a>. They can even remain hidden in the “<a href="https://theconversation.com/explainer-what-is-the-dark-web-46070">dark web</a>”.</p>
<p>Ultimately, there may be no simple technological panacea, except for us each to <a href="https://theconversation.com/we-need-to-take-responsibility-for-our-own-safety-online-38368">maintain vigilance</a>. Although would be little solace to those exposed in the hack of dating website <a href="https://theconversation.com/what-if-the-ashley-madison-hack-was-an-inside-job-46404">Ashley Madison</a>.</p>
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<a href="https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105379/original/image-20151211-8291-1x1t3wj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">They’re getting better at their business.</span>
<span class="attribution"><span class="source">Brian Klug/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
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<h2>True or false?</h2>
<p>But you can’t believe everything you hear. This is especially if it sounds too good to be true, such as that <a href="https://theconversation.com/trolling-our-confirmation-bias-one-bite-and-were-easily-sucked-in-42621">eating chocolate helps you lose weight</a>. Or that <a href="https://theconversation.com/overcoming-the-social-barriers-to-climate-consensus-36889">climate change</a> is not real.</p>
<p>But there are things you can do to protect yourself – or <a href="https://theconversation.com/inoculating-against-science-denial-40465">inoculate yourself</a>, if you will – from anti-science and quackery. There are a few techniques you can use to help <a href="https://theconversation.com/busting-myths-a-practical-guide-to-countering-science-denial-42618">debunk science denial</a> when you see it.</p>
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<a href="https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=387&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=387&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=387&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=487&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=487&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105380/original/image-20151211-8314-15lblrr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=487&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Got to defend against the bad vibes.</span>
<span class="attribution"><span class="source">Bryan Rosengrant/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
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<p>The Abbott government itself hit some bumps when it came to its support for science, particularly when it threatened to cut funding to the National Collaborative Research Infrastructure Strategy, or <a href="https://theconversation.com/explainer-the-national-collaborative-research-infrastructure-strategy-ncris-38837">NCRIS</a>. </p>
<p>Then Education Minister Christopher Pyne was hoping to hold NCRIS ransom to encourage researchers to back his proposed higher education reforms, but the scientific community was as one in its opposition to the cuts, arguing they’d hurt <a href="https://theconversation.com/research-infrastructure-cuts-harm-science-the-economy-and-the-nation-38478">science, the economy and the nation</a> at large.</p>
<p>The government eventually got the message and <a href="https://theconversation.com/pyne-backflips-on-research-infrastructure-funding-cut-38849">capitulated</a>, with Minister Pyne continuing funding in the short term, then solidifying that funding following the change of Prime Minister to Malcolm Turnbull – at which point Christopher Pyne switched to the Innovation, Industry and Science portfolio and changed his tune on research considerably.</p>
<p>In fact, the Turnbull government’s gushing appreciation of science and optimistic spirit when it comes to innovation – backed by <a href="https://theconversation.com/au/topics/innovation-statement">over A$1 billion in funding</a> for science and commercialisation – changed the way <a href="https://theconversation.com/expert-panel-what-the-national-innovation-statement-means-for-science-51902">many scientists felt</a> about the government.</p>
<p>2015 has been a year of milestones and triumphs for science and technology, although laced with a few cautionary messages. We’re now half way through the second decade of the 21st century, and it’s starting to feel like we’re genuinely living in the future – albeit not the future as envisaged by many in the 20th century.</p>
<p>With a new drive for innovation, greater appreciation of the role of science and the emergence of (dare we say) paradigm shifting technologies, such as automation and artificial intelligence, we may feel the lingering traces of the 20th century fall further into the past as 2016 takes over.</p>
<p><strong>Top ten Science + Technology stories by readership in 2015:</strong></p>
<ol>
<li><a href="https://theconversation.com/explainer-what-is-the-dark-web-46070">Explainer: what is the dark web?</a> by <a href="https://theconversation.com/profiles/david-glance-148">David Glance</a></li>
<li><a href="https://theconversation.com/four-easy-tips-to-make-your-batteries-last-longer-41172">Four easy tips to make your batteries last longer</a> by <a href="https://theconversation.com/profiles/valentin-muenzel-130702">Valentin Muenzel</a></li>
<li><a href="https://theconversation.com/its-often-the-puzzles-that-baffle-that-go-viral-40216">It’s often the puzzles that baffle that go viral</a> by <a href="https://theconversation.com/profiles/jonathan-borwein-jon-101">Jon Borwein</a></li>
<li><a href="https://theconversation.com/inskip-beach-collapse-just-dont-call-it-a-sinkhole-48241">Inskip beach collapse: just don’t call it a ‘sinkhole’</a> by <a href="https://theconversation.com/profiles/stephen-fityus-194631">Stephen Fityus</a></li>
<li><a href="https://theconversation.com/the-other-red-meat-on-the-real-palaeodiet-41272">The ‘other’ red meat on the ‘real’ palaeodiet</a> by <a href="https://theconversation.com/profiles/darren-curnoe-2101">Darren Curnoe</a></li>
<li><a href="https://theconversation.com/seven-myths-about-scientists-debunked-37148">Seven myths about scientists debunked</a> by <a href="https://theconversation.com/profiles/marguerite-evans-galea-5223">Marguerite Evans-Galea</a>, <a href="https://theconversation.com/profiles/jeffrey-craig-99410">Jeffrey Craig</a></li>
<li><a href="https://theconversation.com/european-invasion-dna-reveals-the-origins-of-modern-europeans-38096">European invasion: DNA reveals the origins of modern Europeans</a> by <a href="https://theconversation.com/profiles/alan-cooper-18427">Alan Cooper</a>, <a href="https://theconversation.com/profiles/wolfgang-haak-156711">Wolfgang Haak</a></li>
<li><a href="https://theconversation.com/the-verdict-is-in-feel-good-exercise-hormone-irisin-is-real-46082">The verdict is in: feel-good exercise hormone irisin is real</a> by Eliza Berlage</li>
<li><a href="https://theconversation.com/brain-to-brain-interfaces-the-science-of-telepathy-37926">Brain-to-brain interfaces: the science of telepathy</a> by <a href="https://theconversation.com/profiles/kristyn-bates-5106">Kristyn Bates</a></li>
<li><a href="https://theconversation.com/the-smell-of-rain-how-csiro-invented-a-new-word-39231">The smell of rain: how CSIRO invented a new word</a> by <a href="https://theconversation.com/profiles/howard-poynton-157622">Howard Poynton</a></li>
</ol><img src="https://counter.theconversation.com/content/52209/count.gif" alt="The Conversation" width="1" height="1" />
2015 was a year where we expanded our view of the universe, embraced new technologies and got a hint of the profound changes to come.Tim Dean, EditorLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/407362015-04-29T13:44:09Z2015-04-29T13:44:09ZSpace debris: what can we do with unwanted satellites?<figure><img src="https://images.theconversation.com/files/79571/original/image-20150428-3080-eutr4u.jpg?ixlib=rb-1.1.0&rect=0%2C47%2C3508%2C2420&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's crowded up there - the many objects tracked in low Earth orbit.</span> <span class="attribution"><a class="source" href="http://www.esa.int/spaceinimages/Images/2008/03/Debris_objects_-_mostly_debris_-_in_low_Earth_orbit_LEO_-_view_over_the_equator">ESA</a></span></figcaption></figure><p>There are thousands of satellites in Earth orbit, of varying age and usefulness. At some point they reach the end of their lives, at which point they become floating junk. What do we do with them then?</p>
<p>Most satellites are not designed with the end of their life in mind. But some are designed to be serviced, such as the Hubble Space Telescope, which as part of its final service was modified to include a <a href="http://www.spacetelescope.org/about/general/soft_capture/">soft capture mechanism</a>. This is an interface designed to allow a future robotic spacecraft to attach itself and guide the telescope to safe disposal through burn-up in the Earth’s atmosphere once its operational life has ended.</p>
<p>Thinking about methods to retire satellites is important, because without proper disposal they become another source of space debris – fragments of old spacecraft, satellites and rockets now orbiting Earth at thousands of miles per hour. These fragments <a href="http://orbitaldebris.jsc.nasa.gov/faqs.html#3">travel so fast</a> that even a piece the size of a coin has enough energy to disable a whole satellite. There are well over 100,000 pieces this size or larger already orbiting Earth, never mind much larger items – for example the Progress unmanned cargo module, <a href="http://www.space.com/29243-russian-cargo-spacecraft-malfunction-progress59.html">which Russian Space Agency mission controllers have lost control of</a> and which will orbit progressively lower until it burns up in Earth’s atmosphere. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/79572/original/image-20150428-3050-39dc27.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/79572/original/image-20150428-3050-39dc27.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/79572/original/image-20150428-3050-39dc27.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=460&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79572/original/image-20150428-3050-39dc27.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=460&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79572/original/image-20150428-3050-39dc27.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=460&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79572/original/image-20150428-3050-39dc27.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=578&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79572/original/image-20150428-3050-39dc27.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=578&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79572/original/image-20150428-3050-39dc27.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=578&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A hole punched in the side of the SMM satellite by flying orbital debris.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>We don’t know exactly how many or where they are. Only the largest – about 10% of those fragments substantial enough to disable a satellite – can be tracked from the ground. In fact damage to satellites is not unknown, with Hubble and the <a href="http://solarscience.msfc.nasa.gov/SMM.shtml">Solar Maximum Mission</a> (SMM) satellites among those to have coin-sized holes punched into them by flying debris. There is a risk that over the next few years there will be other, perhaps more damaging, collisions.</p>
<p>The soft capture mechanism was installed to prevent more space debris. Engineers worldwide are devising ingenious ways to try to limit the amount of debris orbiting the planet – for good reason. <a href="http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100017146.pdf">Predictions show</a> that if we don’t tackle the problem of space debris then many of our most useful orbits will become too choked with flying fragments for satellites to safely occupy them.</p>
<p>At some point, there may be enough debris in a given orbit for debris-satellite collisions and debris-debris collisions to cascade out of control. This is known as the <a href="http://www.space.com/23039-space-junk-explained-orbital-debris-infographic.html">Kessler syndrome</a>, as shown (in somewhat exaggerated fashion) in the film <a href="http://gravitymovie.warnerbros.com/">Gravity</a>. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/xgGm5odlIh4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Given the degree to which we rely on satellites these days – for communication, GPS and time synchronisation, upon which in turn many vital services such as international banking rely – it’s crucial we prevent near-Earth space from reaching this point. And like it or not, one of the important steps required is to remove large defunct satellites that could become the source of many more chunks of debris.</p>
<h2>Designed for disposal</h2>
<p>Satellites such as the UK’s <a href="http://www.sstl.co.uk/Missions/TechDemoSat-1-Launched-2014">TechDemoSat-1</a> (TDS-1), which launched in 2014, are designed for end-of-life disposal. TDS-1 carries a small drag sail designed and built at Cranfield University that can be deployed once the satellite’s useful science life is over. This acts like a parachute, dragging the satellite’s orbit lower until it re-enters the atmosphere naturally and burns up high in Earth’s atmosphere. </p>
<p>TDS-1 is small enough to burn up – larger or higher satellites will require other ways of moving them away from the most important, valuable, and busy orbits. It’s possible, with enough fuel on-board (and all systems functioning after perhaps decades in space), for satellites to de-orbit themselves. Other, more exotic solutions include tug satellites using nets, tethers, and even <a href="http://ccar.colorado.edu/asen5050/projects/projects_2011/buccino/">high power lasers</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/79573/original/image-20150428-3048-frusin.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/79573/original/image-20150428-3048-frusin.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/79573/original/image-20150428-3048-frusin.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=333&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79573/original/image-20150428-3048-frusin.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=333&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79573/original/image-20150428-3048-frusin.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=333&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79573/original/image-20150428-3048-frusin.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=419&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79573/original/image-20150428-3048-frusin.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=419&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79573/original/image-20150428-3048-frusin.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=419&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Bag it and bin it - ESA’s e.Deorbit project may use nets to collect debris and drag it into the atmosphere to burn up.</span>
<span class="attribution"><span class="source">ESA</span></span>
</figcaption>
</figure>
<p>However, space debris isn’t just an engineering problem. Suppose Europe develops a tug satellite and tries to de-orbit old Russian satellites, or passes close to an active US spy satellite. Clearly this could get political. Simply put, we haven’t yet found a way to use space sustainably, and the problem is almost as complex as finding ways to ensure sustainable development on Earth. What we need are practical solutions – and soon.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/79575/original/image-20150428-3048-igu9yh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/79575/original/image-20150428-3048-igu9yh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=487&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79575/original/image-20150428-3048-igu9yh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=487&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79575/original/image-20150428-3048-igu9yh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=487&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79575/original/image-20150428-3048-igu9yh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=611&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79575/original/image-20150428-3048-igu9yh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=611&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79575/original/image-20150428-3048-igu9yh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=611&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">One that got through: part of the Delta rocket fuel tank that came back to Earth in 1997.</span>
<span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:Debris-deltaInTexas.jpg">NASA</a></span>
</figcaption>
</figure>
<p>So what will happen to Hubble, perhaps the most well-known case of a satellite that requires a retirement plan? One day, perhaps in the early 2020s, a small spacecraft will be launched to rendezvous with the space telescope. It will attach using the soft capture mechanism and then fire its engines to guide Hubble toward re-entry over the South Pacific. For a satellite as large as Hubble, it’s likely that some parts will survive re-entry so a large uninhabited region over the ocean is best suited to avoid risk of damage or casualties.</p>
<p>The re-entry can be tracked carefully from other satellites, aircraft, and ships – all will capture the moment that Hubble itself, having spent decades watching the heavens, will become a bright shooting star for other telescopes to capture. It somehow seems fitting that a mission as remarkable and long-lived as Hubble should itself end in a blaze of glory.</p><img src="https://counter.theconversation.com/content/40736/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stephen Hobbs' work on the TDS-1 satellite (except for payload design and manufacture) was funded by the UK's Technology Strategy Board (now Innovate), and SEEDA. The views in the article represent those of the authors not those of the Research Councils.</span></em></p><p class="fine-print"><em><span>Chiara Palla and Jennifer Kingston do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Near-Earth orbits are filled with useful satellites, and also flying junk. If we’re not careful they may collide - literally.Stephen Hobbs, Senior Lecturer, Course Director in Cyberphysical Systems, Cranfield UniversityChiara Palla, PhD student, Cranfield UniversityJennifer Kingston, Lecturer in aerospace and space systems, Cranfield UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/407242015-04-27T14:33:14Z2015-04-27T14:33:14ZTelescopes on the ground may be cheaper, but Hubble shows why they are not enough<figure><img src="https://images.theconversation.com/files/79104/original/image-20150423-25578-ek0gg9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Bye, Earth telescopes! You will never reach my level.</span> <span class="attribution"><a class="source" href="http://spacetelescope.org/images/hubble_in_orbit1/">ESA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Observatories on Earth are cheaper than telescopes in space. They are also improving rapidly – when the <a href="http://www.eso.org/public/teles-instr/e-elt/">European-Extremely Large Telescope</a> starts its observations in nine years, it will be able to provide images <a href="http://www.eso.org/sci/facilities/eelt/">16 times sharper</a> than those taken by the Hubble space telescope. But while it may seem hard to justify investment in space telescopes, the ground-breaking discoveries made by <a href="http://hubblesite.org/">Hubble</a> have taught us just how valuable they are.</p>
<p>Hubble, which was the world’s first space-based optical observatory, has made amazing discoveries in all aspects of astronomy, from flashes of aurora on planets and moons in our solar system to the evolution of galaxies billions of light years away.</p>
<p>Observations by Hubble helped determine the rate of <a href="http://www.spacetelescope.org/science/age_size/">expansion</a> of the universe in a Nobel prize-winning study. We have witnessed stars being born in nurseries like the <a href="http://hubblesite.org/newscenter/archive/releases/1995/44/">Eagle nebula</a> and exploding as <a href="http://hubblesite.org/newscenter/archive/releases/2005/21/">supernovae</a>. Hubble has also captured a <a href="http://hubblesite.org/newscenter/archive/releases/2000/20/">powerful jet</a> emerging from a black hole at the centre of another galaxy.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/79256/original/image-20150424-14562-177d7ny.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/79256/original/image-20150424-14562-177d7ny.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=613&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79256/original/image-20150424-14562-177d7ny.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=613&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79256/original/image-20150424-14562-177d7ny.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=613&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79256/original/image-20150424-14562-177d7ny.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=770&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79256/original/image-20150424-14562-177d7ny.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=770&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79256/original/image-20150424-14562-177d7ny.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=770&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Picture of the globular cluster Messier 2, taken by Hubble.</span>
<span class="attribution"><a class="source" href="http://www.esa.int/spaceinimages/Images/2015/04/The_crammed_centre_of_Messier_22">ESA/Hubble & NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>These discoveries come at a price. The Hubble mission cost <a href="http://hubblesite.org/the_telescope/hubble_essentials/quick_facts.php">$1.5 billion</a> at its launch in 1990 and the maintenance costs have also been sky-high. The eagerly-anticipated first pictures taken by Hubble were disappointingly blurry. The 2.4 m diameter mirror inside the telescope was slightly flawed so the light was not focusing correctly. Installation of an optics system to correct this problem was the target of the first Hubble servicing mission, carried out by space shuttle astronauts over five days of spacewalks in 1993. Four further servicing missions were carried out from 1997 to 2009 to upgrade and replace scientific instruments, power and guidance systems, and each mission had associated risks and expense. Since the end of NASA’s Space Shuttle programme there has been no way to carry out further servicing.</p>
<p>Space telescopes are not getting any cheaper. The successor to Hubble, the James Webb telescope, has been plagued by a number of delays and rising costs. As it prepares for launch in 2018, it will have cost about <a href="http://jwst.nasa.gov/faq_scientists.html#cost">$8bn</a> to build, launch and commission. </p>
<h2>Earth v space</h2>
<p>One significant advantage of building on the ground is that the size of the telescopes can be much larger than can be carried into space. Telescopes on our own planet have also made amazing discoveries, such as the Gemini telescope observing Jupiter’s two giant red spots <a href="http://www.gemini.edu/index.php?q=node/196">brushing past one another</a> in the planet’s southern hemisphere. The Keck observatory has detected <a href="http://www.keckobservatory.org/recent/entry/detection_of_water_vapor_in_the_atmosphere_of_a_hot_jupiter">water vapour in the atmosphere</a> of a planet orbiting another star. The European Southern Observatory telescopes tracked <a href="http://www.eso.org/public/news/eso0846/">stars orbiting the black hole</a> at the centre of our galaxy to understand the formation of the stars and their interaction with the black hole.</p>
<p>However, ground-based telescopes aren’t cheap either. Work has already begun on the <a href="https://www.eso.org/sci/facilities/eelt/site/">European Extremely Large Telescope</a>, sited in Chile’s Atacama desert, with a cost estimated to be over €1 billion and with annual operating costs of €50m. But this is still less than Hubble and James Webb. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/79259/original/image-20150424-14535-1axh1am.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/79259/original/image-20150424-14535-1axh1am.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=337&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79259/original/image-20150424-14535-1axh1am.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=337&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79259/original/image-20150424-14535-1axh1am.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=337&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79259/original/image-20150424-14535-1axh1am.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79259/original/image-20150424-14535-1axh1am.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79259/original/image-20150424-14535-1axh1am.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of the European Extremely Large Telescope.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/esoastronomy/10181869333/in/photolist-dyxMgh-eiMXuB-gvJK2g-q1MM3G-ckrzoj-n814Vk-psjHyC-6CWtwW-q5vWWk-d2E4Xq-peSeuJ-p1NkHY-mjT5hx-bH7gmP-5DRHXo-e35orX-8wCvVh-jXNaCr-iRDc16-rRBaxZ-biLviH-kbQqKC-2vVkpu-8a2JHg-dAk3K3-gsLgi6-oGwLyV-o11XTS-dCsDZq-qUBjRs-rRw85Z-5NhzDt-r1kXN-sHqv-5YeD34-aNMQZZ-fPqGHR-aNMQxx-8YysNr-8YyDcc-8YBtt9-8YyC46-8YyDna-5DMvHR-9H3sho-b7H6LZ-bDtei8-9CwToe-rvZi3k-biLwJ2">European Southern Observatory/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>When E-ELT <a href="http://www.eso.org/public/teles-instr/e-elt/">observations start</a> in 2024, the state-of-the-art correction for atmospheric distortion will allow it to provide images 16 times sharper than those taken by Hubble. With technological advancements like this it may seem hard to justify the expense and risk of future space-based telescopes. </p>
<p>However, the simple fact is that if we choose to only observe from the ground we will make ourselves blind to a wide variety of astronomical phenomena and potential discoveries. These include some of the universe’s most energetic events, such as gamma ray bursts.</p>
<p>The main reason for this is that the atmosphere of our planet does not hold back space telescopes. While the atmosphere lets through visible light, to which our eyes are sensitive, it absorbs light at some other wavelengths so we can never see it from the ground. In addition, turbulent motion in the atmosphere blurs the light travelling through it, causing objects to twinkle and appear fuzzy. Another problem with ground-based telescopes is that they are subject to local weather conditions, and high clouds can ruin the chance of making any useful observations. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/79430/original/image-20150427-18136-1ssonx4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/79430/original/image-20150427-18136-1ssonx4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79430/original/image-20150427-18136-1ssonx4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79430/original/image-20150427-18136-1ssonx4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79430/original/image-20150427-18136-1ssonx4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79430/original/image-20150427-18136-1ssonx4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79430/original/image-20150427-18136-1ssonx4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Very Large Telescope in Chile is about to get competition from the E-ELT.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/esoastronomy/14494741911/in/photolist-o5RkMi-e35orX-nEPuie-iRDc16-oHywM9-nF6o15-mx6a38-NkGHq-eK6uUe-psjHyC-oUASgZ-dCZi2g-iZGAfm-cP251Q-cP24a5-6zAr9s-91rRzA-91oJ1v-a14a94-dAk3K3-daHxyK-cXNxJE-8cK9Fv-qxoLMF-8cNsDh-oYWdhp-cXN5kU-otKQup-6Z68Po-mwwpu9-aUhuvk-4ufwAb-dxh7au-7DHi3k-dUq43U-rnu1Vf-daHEmZ-4sokd1-6WVThT-8snb98-8sndtt-8sqwUd-8snsB6-e88hWF-72BYzS-dhQfNv-4ZLxAC-9apWLQ-8sntxB-dUq451">ESO/G. Lombardi (glphoto.it)</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>From its vantage point above the atmosphere, Hubble avoids these effects and can produce high-resolution images over a broad spectrum. The scientific value of these observations is evident in that applications by scientists for observing time on Hubble last year were oversubscribed by a factor of five. It has also been an important source of scientific papers. According to a <a href="http://www.eso.org/public/unitedkingdom/announcements/ann15014/">survey by the European Southern Observatory</a> last year, Hubble has produced between 650 and 850 papers per year since 2005 – which is far more than any of ESO’s ground-based telescopes. </p>
<h2>Complementary contributions</h2>
<p>The investment in astronomical telescopes, whether in space or on the ground, has to be justified by the scientific return – and in selecting new facilities it is fundamentally the science which drives the decision. Having worked with telescopes both on the ground and in space, I feel that science ultimately needs both. But in a world of limited funds we can’t have it all. International co-operation is therefore the key, whether it is about placing a new telescope in another country or providing an instrument for a mission led by another space agency. </p>
<p>The value of the observations made by telescopes based both on the ground and in space can be measured not just by the scientific results in understanding the near and far universe, but also in the inspiration that these images and discoveries provide.</p><img src="https://counter.theconversation.com/content/40724/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sarah Badman receives funding from the Royal Astronomical Society and the Science and Technology Facilities Council. However, her views do not represent those of the STFC.</span></em></p>Ground-based telescopes are getting bigger and better while still being cheaper than space telescopes. But the vital scientific contributions made by Hubble demonstrates why we need both.Sarah Badman, Research fellow in space physics, Lancaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/401912015-04-26T11:58:36Z2015-04-26T11:58:36ZHubble’s ultraviolet telescope has revealed more about the stars than we could ever see<figure><img src="https://images.theconversation.com/files/78432/original/image-20150417-3261-3zlzlr.jpg?ixlib=rb-1.1.0&rect=0%2C53%2C1272%2C837&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The galaxies NGC 4038 and NGC 4039, locked in a destructive embrace.</span> <span class="attribution"><a class="source" href="http://www.spacetelescope.org/images/potw1345a/">ESA/Hubble/NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>It’s probably fair to say that the <a href="http://www.spacetelescope.org/">Hubble Space Telescope</a>, which recently celebrated its 25th birthday, has become the world’s most famous telescope in large part due to the <a href="http://www.spacetelescope.org/images/archive/top100">breathtaking astronomical images</a> it has captured. </p>
<p>Hubble’s images reveal the complex, three-dimensional structure of galaxies, nebulae and star-forming regions with incredible acuity, chiefly because the telescope is in space. For ground-based telescopes, the Earth’s atmosphere has a blurring effect, limiting the sharpness of the images they produce. Hubble’s images are limited only by the telescope’s engineering and the properties of light itself.</p>
<p>In 1990 I was privileged to be present at the space shuttle launch which carried Hubble into orbit. The combination of the launch’s powerful demonstration of the defiance of gravity, coupled with the promise of what Hubble would do for astronomy was overwhelming. Curmudgeonly male scientists wept. </p>
<p>Perhaps the affection directed towards Hubble is also partly due to the telescope’s troubled start: the primary mirror was very precisely manufactured, but to the wrong shape. For the first three years of operation, Hubble’s ability to produce sharp images was <a href="http://quest.nasa.gov/hst/about/history.html">compromised</a>, to the point that “Hubble Telescope” was a joke appearing in cartoons and punch-lines. </p>
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<a href="https://images.theconversation.com/files/78428/original/image-20150417-3238-t2hqn5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78428/original/image-20150417-3238-t2hqn5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/78428/original/image-20150417-3238-t2hqn5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=637&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78428/original/image-20150417-3238-t2hqn5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=637&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78428/original/image-20150417-3238-t2hqn5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=637&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78428/original/image-20150417-3238-t2hqn5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=801&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78428/original/image-20150417-3238-t2hqn5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=801&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78428/original/image-20150417-3238-t2hqn5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=801&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Astronauts Hoffman and Musgrave working on the Hubble Space Telescope in 1993.</span>
<span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:Hoffman_and_Musgrave_EVA5.jpg">NASA</a></span>
</figcaption>
</figure>
<p>So engineers produced <a href="http://hubblesite.org/the_telescope/nuts_.and._bolts/optics/costar">COSTAR</a>, a component that would correct the optical problems with the primary mirror. Installed during the first space shuttle visit to Hubble, <a href="http://hubblesite.org/the_telescope/nuts_.and._bolts/optics/costar/#compare">it worked a treat</a>. Like a flawed hero or a prodigal child, Hubble’s triumph over adversity has universal appeal – the best stories, like the best images, have contrasts between darkness and light. </p>
<h2>More than just light</h2>
<p>Fortunately, not all of Hubble’s science had to wait three years for the <a href="https://www.spacetelescope.org/about/history/servicing_mission_1">first servicing mission</a>. Scientific astronomy is carried out in other regions of the electromagnetic spectrum than just visible light, for example ultraviolet (UV) light. UV is invisible to our eyes, but forms the continuation of the visible spectrum beyond the violet. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/78744/original/image-20150421-9017-pjm9pb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78744/original/image-20150421-9017-pjm9pb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/78744/original/image-20150421-9017-pjm9pb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=857&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78744/original/image-20150421-9017-pjm9pb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=857&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78744/original/image-20150421-9017-pjm9pb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=857&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78744/original/image-20150421-9017-pjm9pb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1077&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78744/original/image-20150421-9017-pjm9pb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1077&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78744/original/image-20150421-9017-pjm9pb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1077&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A ‘hot Jupiter’ exoplanet’s atmosphere is stripped away by the heat of its star.</span>
<span class="attribution"><span class="source">ESA/Alfred Vidal-Madjar/NASA</span></span>
</figcaption>
</figure>
<p>Hubble had always been intended to serve as an ultraviolet telescope – from space, UV light that would otherwise be absorbed by Earth’s atmosphere can be collected. Light in this part of the spectrum is more energetic than visible light and is emitted by most stars, including our own, and many other astrophysical objects. Studies in ultraviolet radiation reveal things that can’t be learnt from telescopes on the ground. </p>
<p>Hubble has produced many, many UV science results. My favourite is the spectacular discovery in 2003 that the exoplanet HD209458b is surrounded by a <a href="http://www.spacetelescope.org/images/heic0303a/">huge cloud of hydrogen gas</a>. This type of exoplanet, known as a “hot Jupiter”, orbits its star so closely – only a 20th of the Earth’s distance from the sun – that the star’s heat boils off the planet’s atmosphere.</p>
<h2>Insight into the future</h2>
<p>This sort of discovery offers a great opportunity to <a href="http://hubblesite.org/hubble_discoveries/science_year_in_review/pdf/2010/two_dissipating_exoplanet_atmospheres.pdf">learn what exoplanets are made of</a>. Spectroscopy is the key: each chemical substance has its own spectroscopic fingerprint that allows astronomers to measure chemical compositions – and the UV region of the spectrum is particularly sensitive and useful for this purpose. Hubble has used these strong UV features to reveal the presence of hydrogen, magnesium, iron, silicon and other chemicals in the atmospheres of several hot Jupiter-style exoplanets. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78743/original/image-20150421-9038-1e5ohht.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78743/original/image-20150421-9038-1e5ohht.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78743/original/image-20150421-9038-1e5ohht.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78743/original/image-20150421-9038-1e5ohht.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78743/original/image-20150421-9038-1e5ohht.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78743/original/image-20150421-9038-1e5ohht.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78743/original/image-20150421-9038-1e5ohht.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78743/original/image-20150421-9038-1e5ohht.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Our ultimate fate: a white dwarf star collapsed from a giant red, surrounded by remnants of its inner planets.</span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/2013/18/image/a/">G Bacon/NASA/ESA</a></span>
</figcaption>
</figure>
<p>The loss of the atmosphere of these exoplanets is a preview of the ultimate fate of the Earth, when the sun becomes a red giant star in about four billion years time. As the sun begins to exhaust hydrogen at its core and begins to burn helium, it will swell and become hotter and brighter, engulfing Earth and the inner planets. Once it has exhausted its nuclear fuel, it will collapse into a white dwarf star – about the size of the Earth, and surrounded by the remnants of our solar system.</p>
<p>Hubble UV spectroscopy of white dwarf stars has revealed that many of them are being continually bombarded by asteroids <a href="http://www.astronomynow.com/news/n1203/30whitedwarf">feeding the stars with rocky material</a>. These observations allow us to learn the types of rocks present in extinct planetary systems which were perhaps once very similar to our own solar system. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/78740/original/image-20150421-9051-j2gvmy.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/78740/original/image-20150421-9051-j2gvmy.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78740/original/image-20150421-9051-j2gvmy.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78740/original/image-20150421-9051-j2gvmy.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78740/original/image-20150421-9051-j2gvmy.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78740/original/image-20150421-9051-j2gvmy.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78740/original/image-20150421-9051-j2gvmy.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Appearance in UV of aurorae on Ganymede.</span>
<span class="attribution"><span class="source">NASA/ESA</span></span>
</figcaption>
</figure>
<p>Most recently and closer to home, UV images reveal the <a href="http://www.nasa.gov/sites/default/files/thumbnails/image/15-33i2.png">aurorae around Ganymede</a>, Jupiter’s largest moon. Just as with Earth’s <em>aurora borealis</em> and <em>australis</em> (northern and southern lights), Ganymede’s aurorae change continuously with the influence of Jupiter’s magnetic field. Hubble captured changes in the aurorae caused by the presence of an underground salt-water ocean on Ganymede – an ocean that probably has more water than all of Earth’s oceans combined and may provide a habitat for life. </p>
<p>Hubble has continued its mission well beyond its original planned lifetime. It has made over a million observations and generates about ten terabytes of new data each year. The current plan is for it to operate beyond 2020, to allow some overlap with its replacement, the NASA/ESA/Canadian Space Agency joint project, the <a href="http://www.jwst.nasa.gov">James Webb Space Telescope</a> (JWST). </p>
<p>Sadly for UV astronomy, the JWST will work predominantly in infrared and has no UV instruments. This leaves many astronomers keen to see a successor to Hubble that will continue its unique work in UV, which has added so much to human understanding by working beyond what we can see.</p><img src="https://counter.theconversation.com/content/40191/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Carole Haswell has received funding from the STFC, Nuffield Foundation, and NASA via the Space Telescope Science Institute to perform observations and analysis using the Hubble Space Telescope. She is a member of the Royal Astronomical Society. The views expressed within the article are those of the author and do not represent the views of the Research Councils.</span></em></p>After a slow start, Hubble’s ultraviolet vision changed the face of astronomy.Carole Haswell, Senior Lecturer in Astrophysics, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/404352015-04-23T20:19:43Z2015-04-23T20:19:43ZHubble in pictures: astronomers’ top picks<figure><img src="https://images.theconversation.com/files/79185/original/image-20150423-25578-1kxh3po.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hubble fireworks</span> </figcaption></figure><p>In this special feature, we have invited top astronomers to handpick the Hubble Space Telescope image that has the most scientific relevance to them. The images they’ve chosen aren’t always the colourful glory shots that populate the countless “best of” galleries around the internet, but rather their impact comes in the scientific insights they reveal.</p>
<hr>
<h2>Tanya Hill, Museum Victoria</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/79012/original/image-20150423-1844-1y76nqt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/79012/original/image-20150423-1844-1y76nqt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/79012/original/image-20150423-1844-1y76nqt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79012/original/image-20150423-1844-1y76nqt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79012/original/image-20150423-1844-1y76nqt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79012/original/image-20150423-1844-1y76nqt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79012/original/image-20150423-1844-1y76nqt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79012/original/image-20150423-1844-1y76nqt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NASA,ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team</span></span>
</figcaption>
</figure>
<p>My all-time favourite astronomical object is the <a href="http://hubblesite.org/newscenter/archive/releases/2006/01/full/">Orion Nebula</a> – a beautiful and nearby cloud of gas that is actively forming stars. I was a high school student when I first saw the nebula through a small telescope and it gave me such a sense of achievement to manually point the telescope in the right direction and, after a fair bit of hunting, to finally track it down in the sky (there was no automatic ‘go-to’ button on that telescope). </p>
<p>Of course, what I saw on that long ago night was an amazingly delicate and wispy cloud of gas in black and white. One of the wonderful things that Hubble does is to reveal the <a href="http://hubblesite.org/gallery/behind_the_pictures/meaning_of_color/tool.php">colours of the universe</a>. And this image of the Orion Nebula, is our best chance to imagine what it would look like if we could possibly go there and see it up-close.</p>
<p>So many of Hubble’s images have become iconic, and for me the joy is seeing its beautiful images bring science and art together in a way that engages the public. The entrance to my office, features an enormous copy of this image wallpapered on a wall 4m wide and 2.5m tall. I can tell you, it’s a lovely way to start each working day.</p>
<hr>
<h2>Michael Brown, Monash University</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78885/original/image-20150422-24561-5xg9wl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78885/original/image-20150422-24561-5xg9wl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78885/original/image-20150422-24561-5xg9wl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=560&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78885/original/image-20150422-24561-5xg9wl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=560&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78885/original/image-20150422-24561-5xg9wl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=560&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78885/original/image-20150422-24561-5xg9wl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=704&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78885/original/image-20150422-24561-5xg9wl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=704&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78885/original/image-20150422-24561-5xg9wl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=704&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="http://apod.nasa.gov/apod/ap001105.html">H. Hammel (SSI), WFPC2, HST, NASA</a></span>
</figcaption>
</figure>
<p>The impact of the fragments of <a href="http://solarsystem.nasa.gov/planets/profile.cfm?Object=Com_PShoemakerLevy9">Comet Shoemaker Levy 9</a> with Jupiter in July 1994 was the first time astronomers had advance warning of a planetary collision. Many of the world’s telescopes, including the <a href="http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/archives/sts-61.html">recently repaired Hubble</a>, turned their gaze onto the giant planet.</p>
<p>The comet crash was also my first professional experience of observational astronomy. From a frigid <a href="http://msoheritagetrail.anu.edu.au/telescopes/reynolds-reflector">dome</a> on <a href="http://rsaa.anu.edu.au/observatories/mount-stromlo-observatory">Mount Stromlo</a>, we hoped to see Jupiter’s moons reflect light from comet fragments crashing into the far side of Jupiter. Unfortunately we saw no flashes of light from Jupiter’s moons.</p>
<p>However, Hubble got an amazing and unexpected view. The impacts on the far side of Jupiter produced <a href="http://www.spacetelescope.org/images/opo9430a/">plumes</a> that rose so far above Jupiter’s clouds that they briefly came into view from Earth. </p>
<p>As Jupiter rotated on its axis, enormous dark scars came into view. Each scar was the result of the impact of a comet fragment, and some of the scars were larger in diameter than our moon. For astronomers around the globe, it was a jaw dropping sight.</p>
<hr>
<h2>William Kurth, University of Iowa</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/79001/original/image-20150422-1837-nhai2m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/79001/original/image-20150422-1837-nhai2m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/79001/original/image-20150422-1837-nhai2m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79001/original/image-20150422-1837-nhai2m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79001/original/image-20150422-1837-nhai2m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79001/original/image-20150422-1837-nhai2m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=440&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79001/original/image-20150422-1837-nhai2m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=440&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79001/original/image-20150422-1837-nhai2m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=440&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NASA, ESA and Jonathan Nichols (University of Leicester)</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>This pair of images shows a spectacular ultraviolet aurora light show occurring near Saturn’s north pole in 2013. The two images were taken just 18 hours apart, but show changes in the brightness and shape of the auroras. We used these images to better understand how much of an impact the <a href="http://astronomy.swin.edu.au/cosmos/s/solar+wind">solar wind</a> has on the auroras. </p>
<p>We used Hubble photographs like these acquired by my astronomer colleagues to monitor the auroras while using the <a href="http://saturn.jpl.nasa.gov/">Cassini spacecraft</a>, in orbit around Saturn, to observe <a href="http://www.nasa.gov/mission_pages/cassini/multimedia/pia07966.html">radio emissions associated with the lights</a>. We were able to determine that the brightness of the auroras is correlated with higher radio intensities. </p>
<p>Therefore, I can use Cassini’s continuous radio observations to tell me whether or not the auroras are active, even if we don’t always have images to look at. This was a large effort including many Cassini investigators and Earth-based astronomers. </p>
<hr>
<h2>John Clarke, Boston University</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78476/original/image-20150417-3256-8nx5p.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78476/original/image-20150417-3256-8nx5p.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78476/original/image-20150417-3256-8nx5p.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=352&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78476/original/image-20150417-3256-8nx5p.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=352&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78476/original/image-20150417-3256-8nx5p.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=352&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78476/original/image-20150417-3256-8nx5p.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=442&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78476/original/image-20150417-3256-8nx5p.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=442&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78476/original/image-20150417-3256-8nx5p.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=442&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NASA and John Clarke (Boston University)</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>This far-ultraviolet image of Jupiter’s northern aurora shows the steady improvement in capability of Hubble’s scientific instruments. The Space Telescope Imaging Spectrograph (<a href="http://www.spacetelescope.org/about/general/instruments/stis/">STIS</a>) images showed, for the first time, the full range of auroral emissions that we were just beginning to understand. </p>
<p>The earlier Wide Field Planetary Camera 2 (<a href="http://www.spacetelescope.org/about/general/instruments/wfpc2/">WFPC2</a>) camera had shown that Jupiter’s auroral emissions rotated with the planet, rather than being fixed with the direction to the sun, thus Jupiter did not behave like the Earth. </p>
<p>We knew that there were aurora from the mega-ampere <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/solar/jupmag.html">currents flowing from Io</a> along the magnetic field down to Jupiter, but we were not certain this would occur with the other satellites. While there were many ultraviolet images of Jupiter taken with STIS, I like this one because it clearly shows the auroral emissions from the magnetic footprints of Jupiter’s moons Io, Europa, and Ganymede, and Io’s emission clearly shows the height of the auroral curtain. To me it looks three-dimensional. </p>
<hr>
<h2>Fred Watson, Australian Astronomical Observatory</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78840/original/image-20150421-17614-18058tu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78840/original/image-20150421-17614-18058tu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78840/original/image-20150421-17614-18058tu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=295&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78840/original/image-20150421-17614-18058tu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=295&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78840/original/image-20150421-17614-18058tu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=295&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78840/original/image-20150421-17614-18058tu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=370&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78840/original/image-20150421-17614-18058tu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=370&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78840/original/image-20150421-17614-18058tu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=370&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p>Take a good look at these images of the <a href="https://www.iau.org/public/themes/pluto/">dwarf planet</a>, Pluto, which show detail at the extreme limit of Hubble’s capabilities. A few days from now, they will be old hat, and no-one will bother looking at them again. </p>
<p>Why? Because in early May, the <a href="https://theconversation.com/au/topics/new-horizons">New Horizons</a> spacecraft will be close enough to Pluto for its cameras to reveal better detail, as the craft nears its 14 July rendezvous. </p>
<p>Yet this sequence of images – dating from the early 2000s – has given planetary scientists their best insights to date, the variegated colours revealing subtle variations in Pluto’s surface chemistry. That yellowish region prominent in the centre image, for example, has an excess of frozen carbon monoxide. Why that should be is unknown. </p>
<p>The Hubble images are all the more remarkable given that Pluto is only 2/3 the diameter of our own moon, but nearly 13,000 times farther away.</p>
<hr>
<h2>Chris Tinney, University of New South Wales</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78856/original/image-20150422-9034-vri167.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78856/original/image-20150422-9034-vri167.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78856/original/image-20150422-9034-vri167.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=353&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78856/original/image-20150422-9034-vri167.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=353&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78856/original/image-20150422-9034-vri167.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=353&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78856/original/image-20150422-9034-vri167.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=443&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78856/original/image-20150422-9034-vri167.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=443&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78856/original/image-20150422-9034-vri167.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=443&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">HST / Adam Schneider (University of Toledo)/Chris Tinney (UNSW)</span></span>
</figcaption>
</figure>
<p>I once dragged my wife into my office to proudly show her the results of some imaging observations made at the <a href="http://www.aao.gov.au/about-us/anglo-australian-telescope">Anglo-Australian Telescope</a> with a (then) new and (then) state-of-the-art 8,192 x 8,192 pixel imager. The images were so large, they had to be printed out on multiple A4 pages, and then stuck together to create a huge black-and-white map of a cluster of galaxies that covered a whole wall.</p>
<p>I was crushed when she took one look and said: “Looks like mould”. </p>
<p>Which just goes to show the best science is not always the prettiest.</p>
<p>My choice of the greatest image from HST is another black-and-white image from 2012 that also “looks like mould”. But buried in the heart of the image is an apparently unremarkable faint dot. However it represents the confirmed detection of the coldest example of a <a href="http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/brown_dwarfs.html">brown dwarf</a> then discovered. An object lurking less than 10 <a href="http://astronomy.swin.edu.au/cosmos/P/Parsec">parsecs</a> (32.6 light years) away from the sun with a temperature of about 350 Kelvin (77 degrees Celsius) –- colder than a cup of tea!</p>
<p>And to this day it remains one of the coldest compact objects we’ve detected outside out solar system.</p>
<hr>
<h2>Lucas Macri, Texas A&M University</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78799/original/image-20150421-9005-hj1jxy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78799/original/image-20150421-9005-hj1jxy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78799/original/image-20150421-9005-hj1jxy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=603&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78799/original/image-20150421-9005-hj1jxy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=603&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78799/original/image-20150421-9005-hj1jxy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=603&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78799/original/image-20150421-9005-hj1jxy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=758&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78799/original/image-20150421-9005-hj1jxy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=758&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78799/original/image-20150421-9005-hj1jxy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=758&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NASA/ESA/STScI, processing by Lucas Macri (Texas A&M University). Observations carried out as part of HST Guest Observer program 9810.</span></span>
</figcaption>
</figure>
<p>In 2004, I was part of a team that used the recently-installed Advanced Camera for Surveys (<a href="http://www.spacetelescope.org/about/general/instruments/acs/">ACS</a>) on Hubble to observe a small region of the disk of a nearby spiral galaxy (<a href="http://apod.nasa.gov/apod/ap110319.html">Messier 106</a>) on 12 separate occasions within 45 days. These observations allowed us to discover over <a href="http://dx.doi.org/10.1086/508530">200 Cepheid variables</a>, which are very useful to measure distances to galaxies and ultimately determine the expansion rate of the universe (appropriately named the <a href="http://astronomy.swin.edu.au/cosmos/H/Hubble+Law">Hubble constant</a>). </p>
<p>This method requires a proper calibration of Cepheid luminosities, which can be done in Messier 106 thanks to a very precise and accurate <a href="http://dx.doi.org/10.1088/0004-637X/775/1/13">estimate of the distance</a> to this galaxy (24.8 million light-years, give or take 3%) obtained via radio observations of water clouds orbiting the massive black hole at its center (not included in the image). </p>
<p>A few years later, I was involved in another project that used these observations as the first step in a robust cosmic distance ladder and determined the <a href="http://dx.doi.org/10.1088/0004-637X/730/2/119">value of the Hubble constant</a> with a total uncertainty of 3%.</p>
<hr>
<h2>Howard Bond, Pennsylvania State University</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78949/original/image-20150422-1867-8x9sso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78949/original/image-20150422-1867-8x9sso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78949/original/image-20150422-1867-8x9sso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78949/original/image-20150422-1867-8x9sso.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78949/original/image-20150422-1867-8x9sso.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78949/original/image-20150422-1867-8x9sso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78949/original/image-20150422-1867-8x9sso.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78949/original/image-20150422-1867-8x9sso.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/2003/10/image/i/">NASA, ESA and H.E. Bond (STScI)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>One of the images that excited me most – even though it never became famous – was our first one of the light echo around the strange explosive star <a href="http://hubblesite.org/gallery/tours/tour-v838/">V838 Monocerotis</a>. Its eruption was discovered in January 2002, and its light echo was discovered about a month later, both from small ground-based telescopes. </p>
<p>Although light from the explosion travels straight to the Earth, it also goes out to the side, reflects off nearby dust, and arrives at Earth later, producing the “echo.”</p>
<p>Astronauts had serviced Hubble in <a href="https://www.spacetelescope.org/about/history/servicing_mission_3b/">March 2002</a>, installing the new Advanced Camera for Surveys (<a href="http://www.spacetelescope.org/about/general/instruments/acs/">ACS</a>). In April, we were one of the first to use ACS for science observations. </p>
<p>I always liked to think that NASA somehow knew that the light from V838 was on its way to us from 20,000 light-years away, and got ACS installed just in time! The image, even in only one color, was amazing. We obtained <a href="http://hubblesite.org/newscenter/archive/releases/2004/10/image/a/">many more Hubble observations of the echo</a> over the ensuing decade, and they are some of the most spectacular of all, and VERY famous, but I still remember being awed when I saw this first one.</p>
<hr>
<h2>Philip Kaaret, University of Iowa</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78987/original/image-20150422-1863-fyldsw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78987/original/image-20150422-1863-fyldsw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78987/original/image-20150422-1863-fyldsw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=601&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78987/original/image-20150422-1863-fyldsw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=601&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78987/original/image-20150422-1863-fyldsw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=601&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78987/original/image-20150422-1863-fyldsw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=755&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78987/original/image-20150422-1863-fyldsw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=755&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78987/original/image-20150422-1863-fyldsw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=755&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="http://chandra.harvard.edu/photo/2009/medusa/">X-ray: NASA/CXC/Univ of Iowa/P.Kaaret et al.; Optical: NASA/ESA/STScI/Univ of Iowa/P.Kaaret et al.</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>Galaxies form stars. Some of those stars end their “normal” lives by collapsing into black holes, but then begin new lives as powerful X-ray emitters powered by <a href="https://www-xray.ast.cam.ac.uk/xray_introduction/Blackholebinary.html">gas sucked off a companion star</a>. </p>
<p>I obtained this Hubble image (in red) of the Medusa galaxy to better understand the relation between black hole X-ray binaries and star formation. The striking appearance of the Medusa arises because it’s a collision between two galaxies – the “hair” is remnants of one galaxy torn apart by the gravity of the other. The blue in the image shows X-rays, imaged with the <a href="http://chandra.harvard.edu/photo/2009/medusa/">Chandra X-ray Observatory</a>. The blue dots are black hole binaries. </p>
<p>Earlier work had suggested that the number of X-ray binaries is simply proportional to the rate at which the host galaxy forms stars. These images of the Medusa allowed us to show that the same relation holds, even in the midst of galactic collisions.</p>
<hr>
<h2>Mike Eracleous, Pennsylvania State University</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78529/original/image-20150419-3261-c2uhdm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78529/original/image-20150419-3261-c2uhdm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78529/original/image-20150419-3261-c2uhdm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78529/original/image-20150419-3261-c2uhdm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78529/original/image-20150419-3261-c2uhdm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78529/original/image-20150419-3261-c2uhdm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78529/original/image-20150419-3261-c2uhdm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78529/original/image-20150419-3261-c2uhdm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/2008/16/image/a/">NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Some of the Hubble Space Telescope images that appeal to me a great deal show interacting and merging galaxies, such as the Antennae (<a href="http://www.spacetelescope.org/images/potw1345a/">NGC 4038 and NGC 4039</a>), the Mice (<a href="http://www.spacetelescope.org/images/heic0206h/">NGC 4676</a>), the Cartwheel galaxy (<a href="http://www.spacetelescope.org/images/potw1036a/">ESO 350-40</a>), and many others without nicknames.</p>
<p>These are spectacular examples of violent events that are common in the evolution of galaxies. The images provide us with exquisite detail about what goes on during these interactions: the distortion of the galaxies, the channeling of gas towards their centers, and the formation of stars. </p>
<p>I find these images very useful when I explain to the general public the context of my own research, the <a href="https://solarsystem.nasa.gov/scitech/display.cfm?ST_ID=265">accretion of gas</a> by the supermassive black holes at the centers of such galaxies. Particularly neat and useful is a <a href="http://hubblesite.org/videos/video_details/17-galaxy-collisions-simulation-vs-observations">video</a> put together by Frank Summers at the Space Telescope Science Institute (<a href="http://www.stsci.edu/institute/">STScI</a>), illustrating what we learn by comparing such images with models of galaxy collisions.</p>
<hr>
<h2>Michael Drinkwater, University of Queensland</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78655/original/image-20150420-25694-1nxl4e2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78655/original/image-20150420-25694-1nxl4e2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78655/original/image-20150420-25694-1nxl4e2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78655/original/image-20150420-25694-1nxl4e2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78655/original/image-20150420-25694-1nxl4e2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78655/original/image-20150420-25694-1nxl4e2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78655/original/image-20150420-25694-1nxl4e2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78655/original/image-20150420-25694-1nxl4e2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NASA, Holland Ford (JHU), the ACS Science Team and ESA</span></span>
</figcaption>
</figure>
<p>Our best computer simulations tell us galaxies grow by colliding and merging with each other. Similarly our theories tell us that when two spiral galaxies collide, they should form a large elliptical galaxy. But actually seeing it happen is another story entirely!</p>
<p>This beautiful Hubble image has captured a galaxy collision in action. This doesn’t just tell us that our predictions are good, but it lets us start working out the details because we can now see what actually happens. </p>
<p>There are fireworks of new star formation triggered as the gas clouds collide and huge distortions going on as the spiral arms break up. We have a long way to go before we’ll completely understand how big galaxies form, but images like this are pointing the way.</p>
<hr>
<h2>Roberto Soria, ICRAR-Curtin University</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78861/original/image-20150422-23611-oayew4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78861/original/image-20150422-23611-oayew4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78861/original/image-20150422-23611-oayew4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=627&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78861/original/image-20150422-23611-oayew4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=627&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78861/original/image-20150422-23611-oayew4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=627&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78861/original/image-20150422-23611-oayew4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=787&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78861/original/image-20150422-23611-oayew4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=787&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78861/original/image-20150422-23611-oayew4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=787&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NASA and The Hubble Heritage Team (STScI/AURA)</span></span>
</figcaption>
</figure>
<p>This is the highest-resolution view of a collimated jet powered by a supermassive black hole in the nucleus of the <a href="http://hubblesite.org/newscenter/archive/releases/2008/30/image/f/">galaxy M87</a> (the biggest galaxy in the <a href="http://apod.nasa.gov/apod/ap110422.html">Virgo Cluster</a>, 55 million light years from us). </p>
<p>The jet shoots out of the hot plasma region surrounding the black hole (top left) and we can see it streaming down across the galaxy, over a distance of 6,000 light-years. The white/purple light of the jet in this stunning image is produced by the stream of electrons spiralling around magnetic field lines at a speed of approximately 98% of the speed of light.</p>
<p>Understanding the energy budget of black holes is a challenging and fascinating problem in astrophysics. When gas falls into a black hole, a huge amount of energy is released in the form of visible light, X-rays and jets of electrons and positrons travelling almost at the speed of light. With Hubble, we can measure the size of the black hole (a thousand times bigger than the <a href="http://www.astro.ucla.edu/%7Eghezgroup/gc/journey/smbh.html">central black hole of our galaxy</a>), the energy and speed of its jet, and the structure of the magnetic field that collimates it. </p>
<hr>
<h2>Jane Charlton, Pennsylvania State University</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78948/original/image-20150422-1844-10el753.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78948/original/image-20150422-1844-10el753.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78948/original/image-20150422-1844-10el753.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=946&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78948/original/image-20150422-1844-10el753.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=946&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78948/original/image-20150422-1844-10el753.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=946&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78948/original/image-20150422-1844-10el753.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1189&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78948/original/image-20150422-1844-10el753.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1189&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78948/original/image-20150422-1844-10el753.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1189&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/2001/22/image/a/">NASA, Jayanne English (University of Manitoba), Sally Hunsberger (Pennsylvania State University), Zolt Levay (Space Telescope Science Institute), Sarah Gallagher (Pennsylvania State University), and Jane Charlton (Pennsylvania State University)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>When my Hubble Space Telescope proposal was accepted in 1998 it was one of the biggest thrills of my life. To imagine that, for me, the telescope would capture <a href="http://hubblesite.org/newscenter/archive/releases/2001/22/text/">Stephan’s Quintet</a>, a stunning compact group of galaxies!</p>
<p>Over the next billion years Stephan’s Quintet galaxies will continue in their majestic dance, guided by each other’s gravitational attraction. Eventually they will merge, change their forms, and ultimately become one. </p>
<p>We have since observed several other compact groups of galaxies with Hubble, but Stephan’s Quintet will always be special because its gas has been released from its galaxies and lights up in dramatic bursts of intergalactic star formation. What a fine thing to be alive at a time when we can build the Hubble and push our minds to glimpse the meaning of these signals from our universe. Thanks to all the heroes who made and maintained Hubble.</p>
<hr>
<h2>Geraint Lewis, University of Sydney</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78859/original/image-20150422-9034-13illp2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78859/original/image-20150422-9034-13illp2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78859/original/image-20150422-9034-13illp2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=306&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78859/original/image-20150422-9034-13illp2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=306&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78859/original/image-20150422-9034-13illp2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=306&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78859/original/image-20150422-9034-13illp2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=385&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78859/original/image-20150422-9034-13illp2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=385&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78859/original/image-20150422-9034-13illp2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=385&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NASA, Andrew Fruchter and the ERO Team [Sylvia Baggett (STScI), Richard Hook (ST-ECF), Zoltan Levay (STScI)] (STScI)</span></span>
</figcaption>
</figure>
<p>When Hubble was launched in 1990, I was beginning my PhD studies into <a href="http://imagine.gsfc.nasa.gov/news/grav_lens.html">gravitational lensing</a>, the action of mass bending the paths of light rays as they travel across the universe. </p>
<p>Hubble’s image of the massive galaxy cluster, <a href="http://www.spacetelescope.org/images/heic0814a/">Abell 2218</a>, brings this gravitational lensing into sharp focus, revealing how the massive quantity of <a href="http://astronomy.swin.edu.au/cosmos/D/Dark+Matter">dark matter</a> present in the cluster – matter that binds the many hundreds of galaxies together – magnifies the light from sources many times more distant. </p>
<p>As you stare deeply into the image, these highly magnified images are apparent as long thin streaks, the distorted views of baby galaxies that would normally be impossible to detect. </p>
<p>It gives you pause to think that such gravitational lenses, acting as natural telescopes, use the gravitational pull from invisible matter to reveal amazing detail of the universe we cannot normally see!</p>
<hr>
<h2>Rachel Webster, University of Melbourne</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78858/original/image-20150422-9028-11kda7d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78858/original/image-20150422-9028-11kda7d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78858/original/image-20150422-9028-11kda7d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=406&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78858/original/image-20150422-9028-11kda7d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=406&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78858/original/image-20150422-9028-11kda7d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=406&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78858/original/image-20150422-9028-11kda7d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=510&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78858/original/image-20150422-9028-11kda7d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=510&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78858/original/image-20150422-9028-11kda7d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=510&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/2012/08/image/a/">NASA, ESA, J. Rigby (NASA Goddard Space Flight Center), K. Sharon (Kavli Institute for Cosmological Physics, University of Chicago), and M. Gladders and E. Wuyts (University of Chicago)</a></span>
</figcaption>
</figure>
<p>Gravitational lensing is an extraordinary manifestation of the effect of mass on the shape of space-time in our universe. Essentially, where there is mass the space is curved, and so objects viewed in the distance, beyond these mass structures, have their images distorted. </p>
<p>It’s somewhat like a mirage; indeed this is the term the French use for this effect. In the early days of the Hubble Space Telescope, an image appeared of the lensing effects of a massive cluster of galaxies: the tiny background galaxies were stretched and distorted but embraced the cluster, almost like a pair of hands. </p>
<p>I was stunned. This was a tribute to the extraordinary resolution of the telescope, operating far above the Earth’s atmosphere. Viewed from the ground, these extraordinary thin wisps of galactic light would have been smeared out and not distinguishable from the background noise.</p>
<p>My third year astrophysics class explored the <a href="http://www.spacetelescope.org/images/archive/top100/">100 Top Shots of Hubble</a>, and they were most impressed by the extraordinary, but true colours of the clouds of gas. However I cannot go past an image displaying the effect of mass on the very fabric of our universe.</p>
<hr>
<h2>Kim-Vy Tran, Texas A&M</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78999/original/image-20150422-26679-1q2slxd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78999/original/image-20150422-26679-1q2slxd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78999/original/image-20150422-26679-1q2slxd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=591&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78999/original/image-20150422-26679-1q2slxd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=591&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78999/original/image-20150422-26679-1q2slxd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=591&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78999/original/image-20150422-26679-1q2slxd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=742&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78999/original/image-20150422-26679-1q2slxd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=742&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78999/original/image-20150422-26679-1q2slxd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=742&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/2011/12/">NASA, ESA, J. Richard (Center for Astronomical Research/Observatory of Lyon, France), and J.-P. Kneib (Astrophysical Laboratory of Marseille, France)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>With General Relativity, Einstein postulated that matter changes space-time and can bend light. A fascinating consequence is that very massive objects in the universe will magnify light from distant galaxies, in essence becoming cosmic telescopes.</p>
<p>With the Hubble Space Telescope, we have now harnessed this powerful ability to peer back in time to search for the first galaxies. </p>
<p>This Hubble image shows a hive of galaxies that have enough mass to bend light from very distant galaxies into bright arcs. My first project as a graduate student was to study these remarkable objects, and I still use the Hubble today to explore the nature of galaxies across cosmic time.</p>
<hr>
<h2>Alan Duffy, Swinburne University of Technology</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78657/original/image-20150421-25679-1oyznu4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78657/original/image-20150421-25679-1oyznu4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78657/original/image-20150421-25679-1oyznu4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=548&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78657/original/image-20150421-25679-1oyznu4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=548&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78657/original/image-20150421-25679-1oyznu4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=548&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78657/original/image-20150421-25679-1oyznu4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=688&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78657/original/image-20150421-25679-1oyznu4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=688&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78657/original/image-20150421-25679-1oyznu4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=688&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NASA, ESA, H. Teplitz, M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)</span></span>
</figcaption>
</figure>
<p>To the human eye, the night sky in this image is completely empty. A tiny region no thicker than a grain of rice held at arms length. The Hubble Space Telescope was pointed at this region for 12 full days, letting light hit the detectors and slowly, one by one, the galaxies appeared, until the entire image was filled with 10,000 galaxies stretching all the way across the universe. </p>
<p>The most distant are tiny red dots tens of billions of light years away, dating back to a time just a few hundred million years after the Big Bang. The scientific value of this single image is enormous. It revolutionised our theories both of how early galaxies could form and how rapidly they could grow. The history of our universe, as well as the rich variety of galaxy shapes and sizes, is contained in a single image.</p>
<p>To me, what truly makes this picture extraordinary is that it gives a glimpse into the scale of our visible universe. So many galaxies in so small an area implies that there are 100 thousand million galaxies across the entire night sky. One entire galaxy for every star in our Milky Way!</p>
<hr>
<h2>James Bullock, University of California, Irvine</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78495/original/image-20150418-3212-i6ujwl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78495/original/image-20150418-3212-i6ujwl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78495/original/image-20150418-3212-i6ujwl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=669&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78495/original/image-20150418-3212-i6ujwl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=669&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78495/original/image-20150418-3212-i6ujwl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=669&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78495/original/image-20150418-3212-i6ujwl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=840&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78495/original/image-20150418-3212-i6ujwl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=840&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78495/original/image-20150418-3212-i6ujwl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=840&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/2014/39/image/b/">NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>This is what Hubble <a href="http://hubblesite.org/newscenter/archive/releases/2014/43/full/">is all about</a>. A single, awe-inspiring view can unmask so much about our Universe: its distant past, its ongoing assembly, and even the fundamental physical laws that tie it all together.</p>
<p>We’re peering through the heart of a swarming cluster of galaxies. Those glowing white balls are giant galaxies that dominated the cluster center. Look closely and you’ll see diffuse shreds of white light being ripped off of them! The cluster is acting like a gravitational blender, churning many individual galaxies into a single cloud of stars. </p>
<p>But the cluster itself is just the first chapter in the cosmic story being revealed here. See those faint blue rings and arcs? Those are the distorted images of other galaxies that sit far in the distance.</p>
<p>The immense gravity of the cluster causes the space-time around it to warp. As light from distant galaxies passes by, it’s forced to bend into weird shapes, like a <a href="http://hubblesite.org/newscenter/archive/releases/2014/39/full/">warped magnifying glass</a> would distort and brighten our view of a faint candle. Leveraging our understanding of Einstein’s <a href="https://theconversation.com/explainer-einsteins-theory-of-general-relativity-3481">General Relativity</a>, Hubble is using the cluster as a gravitational telescope, allowing us to see farther and fainter than ever before possible. We are looking far back in time to see galaxies as they were more than 13 billion years ago! </p>
<p>As a theorist, I want to understand the full life cycle of galaxies – how they are born (small, blue, bursting with new stars), how they grow, and eventually how they die (big, red, fading with the light of ancient stars). Hubble allows us to connect these stages. Some of the faintest, most distant galaxies in this image are destined to become monster galaxies like those glowing white in the foreground. We’re seeing the distant past and the present in a single glorious picture.</p><img src="https://counter.theconversation.com/content/40435/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alan Duffy receives funding from Swinburne University of Technology and is affiliated with the Australian Research Council's Centre of Excellence for All-sky Astrophysics.</span></em></p><p class="fine-print"><em><span>Chris Tinney receives funding from the Australian Research Council and the University of NSW</span></em></p><p class="fine-print"><em><span>Geraint Lewis receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Howard E Bond receives funding from NASA through the Space Telescope Science Institute</span></em></p><p class="fine-print"><em><span>James Bullock receives funding from NASA and the NSF.</span></em></p><p class="fine-print"><em><span>Jane Charlton receives funding from the NSF and from NASA.</span></em></p><p class="fine-print"><em><span>John Clarke receives funding from NASA.</span></em></p><p class="fine-print"><em><span>Kim-Vy Tran receives funding from the Space Telescope Science Institute, the National Science Foundation, NASA, and the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University.</span></em></p><p class="fine-print"><em><span>Lucas Macri receives funding from the National Aeronautics and Space Administration and the National Science Foundation of the United States, as well as the Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University.
</span></em></p><p class="fine-print"><em><span>Michael Drinkwater receives funding from The Australian Research Council and The University of Queensland.</span></em></p><p class="fine-print"><em><span>Michael J. I. Brown receives research funding from the Australian Research Council and Monash University, and has developed space-related titles for Monash University's MWorld educational app. He is a fellow of the Astronomical Society of Australia.</span></em></p><p class="fine-print"><em><span>Mike Eracleous receives funding from the National Science Foundation and the National Aeronautics and Space Administration though grants administered by the Space Telescope Science Institute.</span></em></p><p class="fine-print"><em><span>Philip Kaaret receives funding from NASA and the Space Telescope Science Institute. He works for the University of Iowa.
</span></em></p><p class="fine-print"><em><span>Rachel Webster receives funding from the Australian Research Council and the University of Melbourne, and is a Chief Investigator on the ARC Centre of Excellence for all-Sky Astrophysics.</span></em></p><p class="fine-print"><em><span>Roberto Soria receives funding from Curtin University. He is a fellow of the Royal Astronomical Society, the Astronomical Society of Australia, and the Macarthur Astronomical Society.</span></em></p><p class="fine-print"><em><span>William Kurth receives funding from NASA through the Jet Propulsion Laboratory for his work on Cassini. He is a Research Scientist at the University of Iowa</span></em></p><p class="fine-print"><em><span>Fred Watson and Tanya Hill do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Astronomers from around the world identify their favourite images sent back to Earth by the Hubble Space Telescope.Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museums Victoria Research InstituteLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/406792015-04-23T19:10:21Z2015-04-23T19:10:21ZHubble offered a rare, ring-side seat at the death of a star<figure><img src="https://images.theconversation.com/files/79098/original/image-20150423-25549-14eahpc.jpg?ixlib=rb-1.1.0&rect=0%2C162%2C1280%2C1086&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Wreathed in dust, the death of a supergiant star.</span> <span class="attribution"><a class="source" href="http://www.spacetelescope.org/images/heic0405a/">NASA\AURA\STScI\ESA</a></span></figcaption></figure><p>During its impressive 25 years the <a href="http://www.spacetelescope.org/">Hubble Space Telescope</a> has captured numerous remarkable views of the universe, providing astronomers with a wealth of data for making astounding discoveries. Of all the beautiful astronomical objects observed by Hubble one of the most awe-inspiring is the massive, dying star <a href="http://hubblesite.org/newscenter/archive/releases/2005/02/image/a/">V838 Moncerotis</a>.</p>
<p>Hubble’s longevity has provided astronomers with a series of detailed images of V838 Mon captured between May 2002 and September 2006: the result is a fascinating “time-lapse” that uniquely illuminates the evolution of this massive, super-giant star. Hubble’s exceptionally sharp focus of V838 Mon offered a ring-side seat at the slow death of the star and excited astrophysicists with the chance to study the physics of the light, matter and microscopic dust of the interstellar medium.</p>
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<figcaption>
<span class="caption">V838 Monocerotis in April 2002, as the first flash of bright blue light emanates from the star.</span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/2003/10/image/i/">NASA\ESA\H E Bond</a></span>
</figcaption>
</figure>
<p>V838 Mon is about 20,000 light-years away from Earth, in the direction of the constellation of <a href="http://www.constellation-guide.com/constellation-list/monoceros-constellation/">Monoceros</a> (the unicorn). This enormous distance places the star at the outskirts of our galaxy, the Milky Way. In 2002 the star underwent an enigmatic and spectacular brightening, briefly becoming one of the most luminous stars in the Galaxy.</p>
<p>This stellar flash blasted out radiation at a rate 600,000 times the output of our sun. The astounding Hubble images taken over the following years reveal the flash of light illuminating the shells of dust and gas that surround the star.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/U1fvMSs9cps?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
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<p>At first glace, the ring of colour suggests we are witnessing the gradual expansion of the ejected shell of the exploding star. But in fact what are seeing is an extraordinary “<a href="http://hubblesite.org/newscenter/archive/releases/2003/10/">light echo</a>”. </p>
<p>As light from the powerful flash propagates outward at 300,000km per second, it travels through successive rings of dust that surround the star. Some light is scattered by micron-sized dust particles in the dust clouds, reflected back towards the telescope and Earth. The scattered light has travelled a greater distance than the light that arrived directly from the original flash, and so arrives later. This light echo is the optical analogue of the more familiar sound echo, generated when for example thunder bounces of surrounding mountain-sides.</p>
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<a href="https://images.theconversation.com/files/79094/original/image-20150423-25527-1w7u5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/79094/original/image-20150423-25527-1w7u5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/79094/original/image-20150423-25527-1w7u5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=688&fit=crop&dpr=1 600w, https://images.theconversation.com/files/79094/original/image-20150423-25527-1w7u5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=688&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/79094/original/image-20150423-25527-1w7u5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=688&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/79094/original/image-20150423-25527-1w7u5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=864&fit=crop&dpr=1 754w, https://images.theconversation.com/files/79094/original/image-20150423-25527-1w7u5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=864&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/79094/original/image-20150423-25527-1w7u5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=864&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The route the ‘light echo’ took, from star to telescope.</span>
<span class="attribution"><a class="source" href="http://www.spacetelescope.org/images/heic0304f/">NASA\ESA\A Feild</a></span>
</figcaption>
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<p>The light echo discovered by Hubble reveals successive layers of matter and dust, spanning light-years across. The images betray earlier phases in the life of a now ageing, red super-giant star. The latest images in this time-lapse from 2005 and 2006 show an object around about six light-years in diameter, and reveal the turbulent and intricate structure of the interstellar medium, a region where it seems magnetic fields thread the space between stars.</p>
<p>All of these sharp images were taken using the <a href="http://hubblesite.org/the_telescope/nuts_.and._bolts/instruments/acs/">Advanced Camera for Surveys</a> (ACS), which had only just been installed on Hubble during a service mission in March 2002. The images approach true colours by combining data filtered to isolate blue, green and infrared light.</p>
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<figcaption>
<span class="caption">After the initial flash, the light reflected from successively more distant dust clouds reaches Earth.</span>
<span class="attribution"><a class="source" href="http://hubblesite.org/gallery/album/pr2005002g">NASA\ESA\Z Levay</a></span>
</figcaption>
</figure>
<p>The cause of the powerful light flash remains mysterious and debated. One suggestion is that as V838 Mon evolves, its outer layers expand to engulf one or more unseen gas giant planets (or “hot Jupiters”) that may have orbited the star. The subsequent release of the planets’ gravitational energy could result in a brightening of the star, though it’s not certain whether this would be sufficient to explain the magnitude of the light flash. Another scenario is that it may have been the result on an unusual nova-like eruption, where matter from a companion star is pulled by gravity onto the surface of a collapsed white dwarf star, triggering a thermonuclear explosion.</p>
<p>The current leading theory is that a low-mass star, perhaps one-third of the mass of the sun, collided and merged with V838 Mon. The space between stars in enormous compared to the diameter of any star, and therefore stellar collisions are very rare. However, if a pair of stars is born together they will orbit each other, and with loss of orbital energy the low-mass companion may eventually be drawn into the more massive star. The result would be a huge blast of energy.</p>
<p>Transforming from an unremarkable speck in the sky to one of the most extraordinary and beautiful objects, the echoes of V838 Mon will be monitored by astronomers from space telescopes and those on the ground. V838 Mon continues to reveal more to us about the structure of stars, the nature of dust shells spreading into the interstellar medium, and the life – and death – of the most massive stars.</p><img src="https://counter.theconversation.com/content/40679/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Raman Prinja receives research funding from STFC. The views in the article represent those of the author and not those of the Research Councils.</span></em></p>An unremarkable speck in the sky was transformed into an unique astronomical object – and Hubble was there to capture it.Raman Prinja, Professor in Astrophysics, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/405192015-04-23T15:54:32Z2015-04-23T15:54:32ZHubble’s deep field images of the early universe are postcards from billions of years ago<figure><img src="https://images.theconversation.com/files/78767/original/image-20150421-9008-10huvyt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Hubble Extreme Deep Field, looking back towards the birth of the universe.</span> <span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/2012/37/image/a/">NASA/ESA</a></span></figcaption></figure><p>This insignificant patch of sky in the fairly obscure <a href="http://www.topastronomer.com/StarCharts/Constellations/Fornax.php">constellation of Fornax</a> is the setting for one of the most remarkable images ever captured. Although only a fraction of the full moon in size, this image traces thousands of distant galaxies to the edge of the observable universe.</p>
<p>The <a href="http://www.nasa.gov/mission_pages/hubble/story/index.html">Hubble Space Telescope</a> began observing “deep fields” in 1995. The idea was not new – astronomers have always tried to take longer photographic captures that draw in more light to reveal ever more faint and distant objects. Observing more distant galaxies sheds light on how they form, and how their shapes and sizes change over time. Hubble’s key advantage is that, floating in orbit, it’s unaffected by the blurring effect of the atmosphere and so can provide images of far superior resolution than ground-based telescopes.</p>
<p>Careful planning was required for the deep field images. An “empty” piece of sky was needed that contained no bright sources of visible light that might drown out fainter objects. There could also be no bright sources at other wavelengths, such as X-ray or radio waves where complementary supporting observations might be made. The direction chosen was away from the millions of faint stars and dust of the plane of our own galaxy, the Milky Way. </p>
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<figcaption>
<span class="caption">The Hubble Ultra Deep Field, as seen from the ground.</span>
<span class="attribution"><span class="source">Digitised Sky Survey (DSS), STScI/AURA, Palomar/Caltech, and UKSTU/AAO</span></span>
</figcaption>
</figure>
<p>This was not without risk, however. Hubble was, and still is, a hugely popular, world-class research facility. It is typical that demand for Hubble’s instruments outstrips availability by six or seven times. There was always the possibility that the 10 days observation required might reveal the carefully-chosen blank part of the sky to be just that: blank.</p>
<p> </p>
<h2>Even dark skies are filled with stars</h2>
<p>Instead the results of the first Hubble Deep Field image were <a href="http://spacetelescope.org/images/opo9601c/">breathtaking</a>. After stitching together the composite images and careful processing, the final image revealed around 3,000 galaxies, most of which would otherwise have never been seen. This success triggered plans for <a href="http://www.spacetelescope.org/science/deep_fields/">further “deep field” images</a>.</p>
<p>A <a href="http://hubblesite.org/newscenter/archive/releases/1998/41/image/b/">southern-hemisphere counterpart</a> followed in 1998, and after a <a href="http://hubblesite.org/the_telescope/nuts_.and._bolts/instruments/acs/">powerful instrument upgrade</a> in 2002, the Hubble Ultra Deep Field images were taken in 2004. </p>
<p>Finally, advances in data processing techniques, some new infrared data and more images of Ultra Deep Field area were in 2012 combined to create the Hubble eXtreme Deep Field (HXDF), the main image above, and the <a href="http://spacetelescope.org/news/heic1411/">same image with ultraviolet included</a>, below – humanity’s most sensitive images of the cosmos ever taken.</p>
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<figcaption>
<span class="caption">With the addition of IR and UV, this becomes the most colourful view of the universe.</span>
<span class="attribution"><span class="source">NASA\ESA\IPAC\Caltech\STScI\Arizona State University</span></span>
</figcaption>
</figure>
<p> </p>
<h2>Looking out at the cosmos</h2>
<p>The HXDF image is the result of 2m seconds (more than 23 days) of exposure time taken over the course of 2,963 images. The captures that make up the composite image are sensitive to light from the ultraviolet to the near-infrared spectrum, which are used in the processing to create the colours visible. The faintest objects in the HXDF, barely visible on screen, are a remarkable ten-billionth the brightness of the faintest star visible to the naked eye.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/78917/original/image-20150422-1844-1ca1po1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78917/original/image-20150422-1844-1ca1po1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/78917/original/image-20150422-1844-1ca1po1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=444&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78917/original/image-20150422-1844-1ca1po1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=444&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78917/original/image-20150422-1844-1ca1po1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=444&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78917/original/image-20150422-1844-1ca1po1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=558&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78917/original/image-20150422-1844-1ca1po1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=558&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78917/original/image-20150422-1844-1ca1po1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=558&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Twinkle, twinkle, lots of stars (and their diffraction spikes).</span>
<span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:NGC6397.jpg">NASA/ESA/H. Richer</a></span>
</figcaption>
</figure>
<p>A handful of the objects in the image are comparatively “nearby” foreground stars in our own galaxy located perhaps a few tens or hundreds of light-years away. Although the field was chosen to have few of these, some faint stars are present. The stars are quite easy to identify due to the diffraction spikes caused by Hubble’s optics – the tell-tale cross of light across their centre. All the other objects in the image are galaxies.</p>
<p> </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/78930/original/image-20150422-1885-bd3ktn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78930/original/image-20150422-1885-bd3ktn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/78930/original/image-20150422-1885-bd3ktn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=420&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78930/original/image-20150422-1885-bd3ktn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=420&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78930/original/image-20150422-1885-bd3ktn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=420&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78930/original/image-20150422-1885-bd3ktn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=528&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78930/original/image-20150422-1885-bd3ktn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=528&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78930/original/image-20150422-1885-bd3ktn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=528&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">How Hubble’s astronomy looks back in time.</span>
<span class="attribution"><span class="source">NASA/ESA/Z. Levay/F. Summers</span></span>
</figcaption>
</figure>
<p>The image acts a little like a time machine. The further away a galaxy is, the longer it has taken light to reach us – and the earlier in the universe we are looking. Since that light was emitted the universe has continued to expand. Some galaxies in the picture lie close to the edge of the observable universe. This is the furthest point in space to which we could, in principle, see. This is about 45 billion light years from the Earth: light from more distant objects has not yet had time to reach us. </p>
<p> </p>
<h2>Far away and long, long ago</h2>
<p>Some of these galaxies are comparatively near by, perhaps a few hundreds of millions of light years away. These are the bigger objects in the picture: blue or white galaxies with sharply-focused spiral arms, or large red and orange blurs. Galaxies like this are very similar to galaxies we see near the Milky Way.</p>
<p>The most distant objects look very different to galaxies nearer to us, tracing how rapidly galaxies change in the early universe. They shine brightly with the light of young stars, revealing that more stars are formed in the early universe than previously thought. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78778/original/image-20150421-9008-5vowzl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78778/original/image-20150421-9008-5vowzl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78778/original/image-20150421-9008-5vowzl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=394&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78778/original/image-20150421-9008-5vowzl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=394&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78778/original/image-20150421-9008-5vowzl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=394&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78778/original/image-20150421-9008-5vowzl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=495&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78778/original/image-20150421-9008-5vowzl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=495&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78778/original/image-20150421-9008-5vowzl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=495&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A zoom on the HXDF.</span>
<span class="attribution"><span class="source">NASA, ESA, and Z. Levay (STScI)</span></span>
</figcaption>
</figure>
<p>One of these objects, dubbed 39546284 in the zoomed picture above, is thought to be the most distant: it has taken light about 13.3 billion years to reach us (the universe itself is thought to be about 13.7 billion years old). Many of these very young galaxies will eventually evolve into galaxies that look more like the Milky Way.</p>
<p>The image also contains a few supernovae, exploding stars detected more than halfway across the universe. <a href="https://www.nasa.gov/mission_pages/hubble/science/exploding-star.html">SN Primo</a> is one of these, nearly ten billion light years away. Supernovae like these are being used to map out the expansion history of the universe.</p>
<p>Perhaps the most remarkable fact is that this image represents just a tiny fraction of our universe. All told, there are estimated to be some 100 to 200 billion galaxies in the universe, of which only just over 5,000 appear in the HXDF. Put another way, you’d need about 30m images like the HXDF to map the entire sky.</p>
<p>This remarkable image will be one of Hubble’s lasting legacies. With the Space Shuttle now retired from service, there are no future servicing missions planned. This means no future instrument upgrades, so it’s unlikely that Hubble will ever be able to improve significantly on the depth of this image. That honour may await the <a href="http://www.jwst.nasa.gov/">James Webb Space Telescope</a>, scheduled for launch in 2018, and the beginning of another astronomical legacy.</p><img src="https://counter.theconversation.com/content/40519/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Sullivan receives funding from the Royal Society, the European Research Council, and the Science and Technology Facilities Council. Views in the article are those of the author and not those of the Research Councils.</span></em></p>Hubble’s Deep Field images are the next best thing to a time machine, revealing details of galaxies from the early universe, 13 billion years ago.Mark Sullivan, Principal Research Fellow, University of SouthamptonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/402872015-04-22T10:04:11Z2015-04-22T10:04:11ZHubble Space Telescope’s chief scientist on what it took to get the project off the ground<figure><img src="https://images.theconversation.com/files/78266/original/image-20150416-5606-1e4tgwi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hubble in orbit.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/16833954@N00/59115620">NASA</a></span></figcaption></figure><p>Iconic images of astronomical pillars of gas and dust, views of galaxies soon after they were formed, an accelerating universe driven by Dark Energy… “give us more!” say the public and the taxpayers. The <a href="http://www.nasa.gov/mission_pages/hubble/main/index.html">Hubble Space Telescope</a> is undoubtedly one of the most popular science projects today. It was not always thus. </p>
<h2>Laying the groundwork</h2>
<p>With its origins dating back to a time when almost all astronomers used photographic plates to record images at ground-based telescopes, the idea of an ambitious and expensive observatory in space was not a popular one. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/78260/original/image-20150416-5628-1lzvrzf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78260/original/image-20150416-5628-1lzvrzf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/78260/original/image-20150416-5628-1lzvrzf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78260/original/image-20150416-5628-1lzvrzf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78260/original/image-20150416-5628-1lzvrzf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78260/original/image-20150416-5628-1lzvrzf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78260/original/image-20150416-5628-1lzvrzf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78260/original/image-20150416-5628-1lzvrzf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Palomar Observatory, firmly rooted to the ground.</span>
<span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:Palomar_Observatory_2.jpg">Tylerfinvold</a></span>
</figcaption>
</figure>
<p>The most influential astronomers of the 1960s thought it better to spend the money on 15 copies of the 200-inch giant on Palomar Mountain, rather than gamble all on a single telescope in space that was not as large. </p>
<p>Nevertheless, NASA held out the Hubble as a <a href="http://www.nasa.gov/mission_pages/hubble/story/the_story.html">long-term goal</a>. By the early 1970s, things began to change as preliminary designs for the spacecraft were generated and my colleagues were educated about the Hubble’s potential. </p>
<p>This space-based telescope would be able to make images of a step up in quality that was as great as Galileo’s application of the first astronomical telescope was to the view with an unaided eye. It would detect stars and galaxies that lay beyond the limit of faintness of giant ground-based observatories. I left my professorship at the University of Chicago in 1972 to become the scientific leader of the proposed project and considered the gathering of scientific support my most important immediate job.</p>
<p>Finally the idea caught on and scientists and groups from most of the major observatories in the US and Europe became involved with building the observatory, its individual scientific instruments, and planning the science to be done. From widespread skepticism, the situation changed to astronomers not wanting to miss the boat.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78401/original/image-20150417-3241-shi6o5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78401/original/image-20150417-3241-shi6o5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78401/original/image-20150417-3241-shi6o5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=319&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78401/original/image-20150417-3241-shi6o5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=319&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78401/original/image-20150417-3241-shi6o5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=319&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78401/original/image-20150417-3241-shi6o5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=401&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78401/original/image-20150417-3241-shi6o5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=401&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78401/original/image-20150417-3241-shi6o5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=401&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Hubble Space Telescope was designed to be able to probe deeper into the universe’s past than anything based on the ground.</span>
<span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:Hubble_Probes_the_Early_Universe.jpg">NASA</a></span>
</figcaption>
</figure>
<p>The first few years were spent in preliminary design of many types of scientific instruments, using competitively selected scientists. As we moved into the selection of teams to build the instruments, we held a new competition. The teams who had proposed the most modern approaches were selected, leaving behind some people involved since the earliest studies.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78397/original/image-20150417-3249-1whcyno.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78397/original/image-20150417-3249-1whcyno.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78397/original/image-20150417-3249-1whcyno.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78397/original/image-20150417-3249-1whcyno.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78397/original/image-20150417-3249-1whcyno.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78397/original/image-20150417-3249-1whcyno.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78397/original/image-20150417-3249-1whcyno.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78397/original/image-20150417-3249-1whcyno.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Polishing Hubble’s eight-foot diameter mirror, designed to focus the faint light the telescope would encounter in space.</span>
<span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:Hubble_mirror_polishing.jpg">NASA Marshall Space Flight Center</a></span>
</figcaption>
</figure>
<p><a href="http://hubblesite.org/the_telescope/nuts_.and._bolts/">Hardware</a> began to be built in 1977, even before the Hubble was funded by Congress in fiscal year 1978. Preparations proceeded on the bumpy and expensive path that would lead to its being ready for launch in late 1986. But then the space shuttle Challenger accident occurred and several years of delay ensued as the <a href="http://www.nasa.gov/externalflash/the_shuttle/">Space Transportation System</a> came back into operation. Hubble eventually hitched a ride to space onboard Space Shuttle Discovery in April, 1990.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78269/original/image-20150416-5654-1g9iqsj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78269/original/image-20150416-5654-1g9iqsj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78269/original/image-20150416-5654-1g9iqsj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=475&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78269/original/image-20150416-5654-1g9iqsj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=475&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78269/original/image-20150416-5654-1g9iqsj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=475&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78269/original/image-20150416-5654-1g9iqsj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=596&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78269/original/image-20150416-5654-1g9iqsj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=596&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78269/original/image-20150416-5654-1g9iqsj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=596&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">On the right is part of the first image taken with NASA’s Hubble Space Telescope’s Wide Field/Planetary Camera. Compare with a ground-based picture from Las Campanas, Chile, Observatory of the same region of the sky.</span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/1990/1990/04/image/a/">Right: NASA, ESA, and STScI Left: E. Persson (Las Campanas Observatory, Chile)/Observatories of the Carnegie Institution of Washington</a></span>
</figcaption>
</figure>
<h2>Bumpy ride at first</h2>
<p>Within a few weeks it looked like those early skeptics were the wise ones amongst us. The telescope’s primary mirror had been created with great precision and measured with unprecedented accuracy; but the measuring equipment was misaligned. That error resulted in a mirror that formed a degraded image. Instead of a single sharp core where 90% of the light focused, there was a sharp core with 20% of the light surrounded by a halo. We were pilloried, investigated, and a subject of mean-spirited cartoons. Techno-Turkey was a popular description.</p>
<p>However, researchers developed computer programs to accurately remove the halo and the scientific value of the resulting images began to be appreciated. Over the next several years the articles on the Hubble changed from the initial subjects of “how can such a major screw-up occur,” to lead-ins of “the crippled Hubble has shown this interesting scientific result,” until finally the science stories would simply end with a mention in the last paragraph that the Hubble was working with a flawed mirror, but it was expected that things would be improved after the first servicing mission.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78405/original/image-20150417-3261-qxglm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78405/original/image-20150417-3261-qxglm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78405/original/image-20150417-3261-qxglm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=403&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78405/original/image-20150417-3261-qxglm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=403&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78405/original/image-20150417-3261-qxglm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=403&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78405/original/image-20150417-3261-qxglm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=507&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78405/original/image-20150417-3261-qxglm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=507&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78405/original/image-20150417-3261-qxglm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=507&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Astronauts remove the Wide Field and Planetary Camera to replace it with its more powerful successor, Wide Field and Planetary Camera 2, during Hubble’s first servicing mission in 1993.</span>
<span class="attribution"><a class="source" href="http://hubblesite.org/gallery/spacecraft/15/">STScI</a></span>
</figcaption>
</figure>
<p>And improve they did with the servicing mission of December 1993. That success reflected the finest hours (years actually) of NASA and Aerospace engineers and managers, the <a href="http://www.stsci.edu/hst">Space Telescope Science Institute</a> and the Astronaut Corps. The scientific instruments were housed in easily changed-out boxes. An empty instrument box had been made before the 1990 launch to be used in case one of the scientific instruments was not ready in time. </p>
<p>This box was altered to house a set of mirrors that would correct the convergent light beam coming from the flawed primary mirror so it would reach the scientific instruments in pristine condition. A backup imaging camera was installed that had the correction figured into the internal mirrors that were already part of its design. The Hubble was saved and was actually producing images better than we had publicly predicted.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78262/original/image-20150416-5615-qlu8z2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78262/original/image-20150416-5615-qlu8z2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78262/original/image-20150416-5615-qlu8z2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=321&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78262/original/image-20150416-5615-qlu8z2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=321&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78262/original/image-20150416-5615-qlu8z2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=321&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78262/original/image-20150416-5615-qlu8z2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=403&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78262/original/image-20150416-5615-qlu8z2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=403&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78262/original/image-20150416-5615-qlu8z2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=403&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This comparison image of the core of the galaxy M100 shows the dramatic improvement in Hubble Space Telescope’s view of the universe after the first Hubble Servicing Mission in December 1993.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/nasacommons/9460789088">NASA</a></span>
</figcaption>
</figure>
<h2>Back in business</h2>
<p>Happily, the rest is history.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/78271/original/image-20150416-5615-qfr3gm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78271/original/image-20150416-5615-qfr3gm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/78271/original/image-20150416-5615-qfr3gm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=626&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78271/original/image-20150416-5615-qfr3gm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=626&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78271/original/image-20150416-5615-qfr3gm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=626&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78271/original/image-20150416-5615-qfr3gm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=786&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78271/original/image-20150416-5615-qfr3gm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=786&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78271/original/image-20150416-5615-qfr3gm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=786&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The iconic Pillars of Creation image taken by the Hubble.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/gsfc/16189387096">NASA, ESA, and the Hubble Heritage Team (STScI/AURA)</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The four additional <a href="http://hubblesite.org/the_telescope/team_hubble/servicing_missions.php">servicing missions</a> have replaced failed components, repaired instruments in-orbit, and replaced support-equipment (for example the data recorders and computers) and scientific instruments, so that today’s Hubble is more powerful than ever. Without the ability to conduct additional servicing missions, its lifetime will be limited. Whatever time we still have will be welcome, but in any event, the Hubble Space Telescope must be considered a triumph.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/78273/original/image-20150416-5660-14bq7kv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78273/original/image-20150416-5660-14bq7kv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/78273/original/image-20150416-5660-14bq7kv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78273/original/image-20150416-5660-14bq7kv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78273/original/image-20150416-5660-14bq7kv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78273/original/image-20150416-5660-14bq7kv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78273/original/image-20150416-5660-14bq7kv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78273/original/image-20150416-5660-14bq7kv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A Hubble image of a proplyd in the Orion Nebula.</span>
<span class="attribution"><a class="source" href="http://hubblesite.org/newscenter/archive/releases/1995/45/image/d/">Mark McCaughrean (Max-Planck-Institute for Astronomy), C. Robert O'Dell (Rice University), and NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>It has been gratifying to be on the ground floor of the Hubble project and to shape the direction that it’s taken. Engineering images of my favorite astronomical object, the Orion Nebula, were made before that first servicing mission. I was given access to those and in their analysis discovered the objects now called proplyds. These are the circumstellar material and proto-planetary disks surrounding very young stars (ages much less than one million years).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78400/original/image-20150417-3241-zsg07s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78400/original/image-20150417-3241-zsg07s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78400/original/image-20150417-3241-zsg07s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=442&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78400/original/image-20150417-3241-zsg07s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=442&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78400/original/image-20150417-3241-zsg07s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=442&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78400/original/image-20150417-3241-zsg07s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=556&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78400/original/image-20150417-3241-zsg07s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=556&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78400/original/image-20150417-3241-zsg07s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=556&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hubble over Earth in 2009.</span>
<span class="attribution"><a class="source" href="http://hubble25th.org/resources/1">STScI</a></span>
</figcaption>
</figure>
<p>These discoveries started a series of investigations using the Hubble that continues today. I’ve just submitted a paper on the most recent of these for publication. It exploits the fact that the long difference in time between the earliest and most recent images allows us to see changes in the nebula and to trace the matter being expelled from the youngest of the stars in Orion, thus illuminating the process by which stars and their planets are formed.</p>
<p>It’s just one of the discoveries we certainly wouldn’t have made by now without a space telescope like the Hubble.</p><img src="https://counter.theconversation.com/content/40287/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>C Robert O'Dell receives funding from NASA.</span></em></p>The Hubble Space Telescope launched 25 years ago in 1990. But O'Dell started on the project in 1972, garnering support for the world’s first telescope free of Earth’s atmosphere’s blurring effects.C Robert O'Dell, Research Professor of Physics and Astronomy, Vanderbilt UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/403122015-04-22T02:06:57Z2015-04-22T02:06:57ZWhy the Hubble Space Telescope has been such a stellar success<figure><img src="https://images.theconversation.com/files/78677/original/image-20150421-25708-1rceaxw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Hubble Space Telescope hovers at the boundary of Earth and space.</span> <span class="attribution"><a class="source" href="http://hubblesite.org/gallery/spacecraft/06/">NASA</a></span></figcaption></figure><p>When the <a href="http://hubblesite.org/">Hubble Space Telescope</a> was launched back in April 1990 the <a href="http://webfoundation.org/about/vision/history-of-the-web/">World Wide Web</a> was just months old and iPads existed only on <a href="http://arstechnica.com/apple/2010/08/how-star-trek-artists-imagined-the-ipad-23-years-ago/">Star Trek</a>.</p>
<p>At first glance, Hubble is from a different technological era and yet it continues to produce dazzling science and has global recognition. Indeed, when Hubble appears in the opening scenes of <a href="http://www.space.com/23062-gravity-movie-science-fiction-fact.html">Gravity</a>, the film’s audience needs no explanation. </p>
<p>Why has Hubble been so successful for so long? How does it continue to make amazing discoveries that capture our imagination after decades in space? </p>
<h2>Renewal</h2>
<p>Hubble has been in space for 25 years, but in many ways is far younger. <a href="http://www.nasa.gov/mission_pages/shuttle/main/">Space shuttle</a> crews have serviced <a href="http://hubblesite.org/the_telescope/team_hubble/servicing_missions.php">Hubble five times</a> between 1993 and 2009, replacing old equipment and making repairs.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78682/original/image-20150421-25701-18f32y1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78682/original/image-20150421-25701-18f32y1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78682/original/image-20150421-25701-18f32y1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=819&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78682/original/image-20150421-25701-18f32y1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=819&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78682/original/image-20150421-25701-18f32y1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=819&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78682/original/image-20150421-25701-18f32y1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1029&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78682/original/image-20150421-25701-18f32y1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1029&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78682/original/image-20150421-25701-18f32y1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1029&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Story Musgrave and Jeffrey Hoffman repair Hubble above Western Australia in 1993.</span>
<span class="attribution"><a class="source" href="http://apod.nasa.gov/apod/ap960128.html">NASA, STS-61 Crew</a></span>
</figcaption>
</figure>
<p>Hubble’s mission started with embarrassment, when it was launched with a mirror that was the <a href="http://www.nytimes.com/1990/11/28/us/panel-on-space-telescope-cites-flaws-in-management.html">wrong shape</a>. The error was only 0.002 millimetres, which may seem tiny, but is large for precision optics. </p>
<p>Fortunately, the mirror’s defects were well understood, so <a href="http://hubblesite.org/the_telescope/nuts_.and._bolts/optics/costar/">lenses were made</a> to correct Hubble’s near-sightedness. Spacewalking astronauts installed these lenses into Hubble during the first servicing mission in 1993. </p>
<p>Astronauts have also replaced <a href="http://www.esa.int/Our_Activities/Space_Engineering_Technology/How_Hubble_got_its_wings">jittery solar arrays</a> and <a href="http://asd.gsfc.nasa.gov/archive/sm3a/sm3a_fact_sheets.html#gyroscopes">failing gyroscopes</a>. Old detectors have been replaced with more modern instruments. </p>
<p>Other equipment has been brought back to life, with spacewalking astronauts replacing defective electronics and <a href="http://asd.gsfc.nasa.gov/archive/hubble/ncs-story/event-03.html">installing upgrades</a>. Such work is no mean feat in bulky pressurised spacesuits, and the Hubble servicing missions are one of the triumphs of crewed spaceflight. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/CYLMXCqkuBg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The crew of Atlantis conducted the last Hubble service mission in 2009.</span></figcaption>
</figure>
<p>Without these servicing missions, Hubble would never have produced spectacular science. Even if the mirror had been perfect, instruments would have become obsolete and the gyroscopes (essential for orienting Hubble) would have failed. </p>
<p>Since the retirement of the shuttles, Hubble can no longer be serviced. It may function for many years yet, but it will someday fail and eventually meet its end in a fiery re-entry.</p>
<h2>A clear view from space</h2>
<p>On a clear night in the countryside, you may imagine you have an unhindered view of the universe. But even on the clearest of nights, starlight is being absorbed and scattered by our atmosphere. Our atmosphere makes stars <a href="http://apod.nasa.gov/apod/ap000725.html">twinkle</a> and scatters blue sunlight so effectively that the entire <a href="http://spaceplace.nasa.gov/blue-sky/en/">daytime sky is blue</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78676/original/image-20150421-25721-c39buw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78676/original/image-20150421-25721-c39buw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78676/original/image-20150421-25721-c39buw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=626&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78676/original/image-20150421-25721-c39buw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=626&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78676/original/image-20150421-25721-c39buw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=626&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78676/original/image-20150421-25721-c39buw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=787&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78676/original/image-20150421-25721-c39buw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=787&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78676/original/image-20150421-25721-c39buw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=787&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hubble has advantages over most telescopes when it comes to making detailed images of celestial objects like the Eagle Nebula.</span>
<span class="attribution"><a class="source" href="http://hubblesite.org/gallery/album/pr2015001c/">NASA, ESA, and the Hubble Heritage Team (STScI/AURA)</a></span>
</figcaption>
</figure>
<p>Unlike Hubble, telescopes on Earth must peer through our turbulent atmosphere, which blurs images. Centuries ago, Isaac Newton <a href="http://www.gutenberg.org/files/33504/33504-h/33504-h.htm">realised the atmosphere hinders</a> the ability of telescopes to resolve details, and he suggested a solution:</p>
<blockquote>
<p>The only Remedy is a most serene and quiet Air, such as may perhaps be found on the tops of the highest Mountains above the grosser Clouds.</p>
</blockquote>
<p>While astronomers do place telescopes atop of high mountains, the ultimate solution is a telescope in space. In space, the clarity of Hubble’s images (defined by <a href="http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/resolution.html">angular resolution</a>) is <a href="http://en.wikipedia.org/wiki/Diffraction-limited_system">limited by the size</a> of its 2.4 metre mirror rather than atmospheric turbulence. From this vantage point, in visible light Hubble can see details roughly 25 times smaller than most Earth-bound telescopes can.</p>
<p>Being in space gives Hubble incredible advantages compared to Earth-bound telescopes. But Hubble isn’t meaningfully closer to the stars than us. It’s just 540 kilometres above the Earth, which is nothing compared to <a href="https://theconversation.com/explainer-light-years-and-units-for-the-stars-16995">astronomical distances</a>. Indeed, it’s so close <a href="http://www.heavens-above.com">you can sometimes spot Hubble</a> speeding by.</p>
<p>In the 1990s, a team of astronomers, led by <a href="http://gruber.yale.edu/cosmology/2009/wendy-l-freedman">Wendy Freedman</a>, <a href="http://gruber.yale.edu/cosmology/2009/robert-c-kennicutt">Rob Kennicutt</a> and <a href="http://gruber.yale.edu/cosmology/2009/jeremy-mould">Jeremy Mould</a>, exploited the clarity of Hubble’s images to find the <a href="http://hubblesite.org/newscenter/archive/releases/1994/49/image/a/">bright variable stars</a> in galaxies millions of light years from Earth. With these stars, astronomers measured the distances to these galaxies, which enabled the first precision measurement of the expansion rate of the Universe.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78156/original/image-20150416-31691-h1sm7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78156/original/image-20150416-31691-h1sm7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78156/original/image-20150416-31691-h1sm7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78156/original/image-20150416-31691-h1sm7a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78156/original/image-20150416-31691-h1sm7a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78156/original/image-20150416-31691-h1sm7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78156/original/image-20150416-31691-h1sm7a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78156/original/image-20150416-31691-h1sm7a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hubble is able to identify bright stars in galaxies such as Messier 100.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>The detail of Hubble’s images has been crucial to its ongoing success. It has enabled astronomers to view <a href="http://hubblesite.org/newscenter/archive/releases/2003/17/image/c/">changing weather</a> and <a href="http://hubblesite.org/gallery/album/solar_system/jupiter/pr2000038a/">aurora</a> on other planets, measure the gravitational <a href="https://theconversation.com/shedding-new-light-on-the-search-for-the-invisible-dark-matter-40083">deflection of light by dark matter</a>, peer into <a href="http://hubblesite.org/newscenter/archive/releases/2015/01/full/">stellar nurseries</a> and glimpse <a href="http://www.nasa.gov/mission_pages/hubble/science/fomalhaut-exo.html">planets orbiting other stars</a>. </p>
<h2>Innovations</h2>
<p>For the past two decades astronomers have been discovering <a href="https://theconversation.com/exoplanets-how-the-search-for-life-became-sexy-43">planets orbiting distant stars</a>. Some of these planets <a href="http://www.nasa.gov/mission_pages/kepler/multimedia/images/kepler-transit-graph_prt.htm">transit</a>, passing between their stars and us, so they block a tiny percentage of the starlight that we would otherwise see. Transits that cause stars to dim by 1% are regularly detected by ground-based telescopes.</p>
<p>A far greater challenge is detecting the almost imperceptible additional dimming during a transit caused by light being blocked by particular elements and molecules in a planet’s atmosphere. This requires measuring a 0.01% change in brightness: a perfect job for Hubble in the vacuum of space.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/78167/original/image-20150416-23326-12lmczf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78167/original/image-20150416-23326-12lmczf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78167/original/image-20150416-23326-12lmczf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=356&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78167/original/image-20150416-23326-12lmczf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=356&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78167/original/image-20150416-23326-12lmczf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=356&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78167/original/image-20150416-23326-12lmczf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=447&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78167/original/image-20150416-23326-12lmczf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=447&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78167/original/image-20150416-23326-12lmczf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=447&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hubble has detected the atmospheres of worlds circling distant stars.</span>
<span class="attribution"><span class="source">NASA; ESA; G. Bacon, STScI</span></span>
</figcaption>
</figure>
<p>In 2000, <a href="https://www.cfa.harvard.edu/%7Edcharbon/Site/Welcome.html">David Charbonneau</a>, <a href="https://www2.ucar.edu/atmosnews/people/tim-brown">Tim Brown</a> and their colleagues used Hubble to <a href="http://hubblesite.org/newscenter/archive/releases/2001/38/text/">detect sodium in the atmosphere of a planet</a> orbiting the star HD 209458.</p>
<p>This is incredibly innovative science, which was not imagined by Hubble’s designers four decades ago, when the only known planets were in our own solar system. Astronomers finding new ways to exploit Hubble’s unique advantages is a key reason for Hubble’s <a href="http://www.stsci.edu/institute/conference/hubble25/scientific-program">continuing success</a>.</p>
<h2>Light and dark</h2>
<p>When we look at the night sky, we are seeing only a small portion of the <a href="https://theconversation.com/explainer-what-is-the-electromagnetic-spectrum-8046">spectrum of light</a>. Ultraviolet and infrared light is invisible to our eyes. Even if we could see ultraviolet light, it is largely blocked by the ozone layer. </p>
<p>Furthermore, when we look up at the stars, we don’t just see the starlight. We can see dark trees silhouetted against the night sky. The air literally glows, and it is particularly bright in infrared light. </p>
<p>From its vantage point in space, Hubble can see a broad spectrum of light against an exceptionally dark sky. This allows it to see further than Earth-bound telescopes.</p>
<p>In late 1995, Hubble’s director, <a href="http://www.stsci.edu/%7Ewms/">Bob Williams</a>, used Hubble to stare at one region of space for ten consecutive days. The images of the “<a href="http://hubblesite.org/hubble_discoveries/hubble_deep_field/">Hubble Deep Field</a>” revealed thousands of galaxies, some of which are 12 billion light years from Earth.</p>
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<a href="https://images.theconversation.com/files/78189/original/image-20150416-5615-3fwb8q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/78189/original/image-20150416-5615-3fwb8q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/78189/original/image-20150416-5615-3fwb8q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=616&fit=crop&dpr=1 600w, https://images.theconversation.com/files/78189/original/image-20150416-5615-3fwb8q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=616&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/78189/original/image-20150416-5615-3fwb8q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=616&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/78189/original/image-20150416-5615-3fwb8q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=774&fit=crop&dpr=1 754w, https://images.theconversation.com/files/78189/original/image-20150416-5615-3fwb8q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=774&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/78189/original/image-20150416-5615-3fwb8q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=774&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">There are only two stars visible in this image. The rest are galaxies.</span>
<span class="attribution"><span class="source">Robert Williams and the Hubble Deep Field Team (STScI) and NASA</span></span>
</figcaption>
</figure>
<p>With improved instrumentation, Hubble has been able to stare even further into space, seeing galaxies <a href="http://hubblesite.org/newscenter/archive/releases/cosmology/distant-galaxies/2012/48/">13.3 billion light years</a> from Earth. This means the light took 97% of the age of the Universe to travel from these galaxies to Hubble. We are also seeing these galaxies when the Universe was 3% of its current age. </p>
<p>Hubble’s successor, the James Webb Space Telescope, will peer further into space and back in time, viewing the creation of the first stars and galaxies.</p><img src="https://counter.theconversation.com/content/40312/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael J. I. Brown receives research funding from the Australian Research Council and Monash University, and has developed space-related titles for Monash University's MWorld educational app.</span></em></p>Twenty-five years on and the Hubble Space Telescope is still taking some amazing images. But there have been a few glitches over the years, right from day one.Michael J. I. Brown, Associate professor, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.