tag:theconversation.com,2011:/us/topics/ground-based-telescopes-16406/articlesGround-based telescopes – The Conversation2022-05-19T13:08:31Ztag:theconversation.com,2011:article/1832482022-05-19T13:08:31Z2022-05-19T13:08:31ZHow visionary scientist Bernie Fanaroff put African astronomy on the map<figure><img src="https://images.theconversation.com/files/463595/original/file-20220517-6201-dk0n1u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Without Dr Bernie Fanaroff, the SKA might never have come to South African shores</span> <span class="attribution"><span class="source">Foto24/Gallo Images/Getty Images</span></span></figcaption></figure><p>Recent decades have seen remarkable growth in astronomy on the African continent. Africa enjoys pristine dark skies and vast radio quiet zones, making it the ideal home for many advanced telescopes trained on our galaxy and beyond.</p>
<p>For instance, Namibia hosts the <a href="https://www.mpi-hd.mpg.de/hfm/HESS/">High Energy Spectroscopic System</a> (HESS), which is an impressive gamma-ray telescope. The <a href="https://www.salt.ac.za/">Southern African Large Telescope</a> (SALT) in the small South African town of Sutherland is the largest optical telescope in the southern hemisphere. The <a href="https://www.sarao.ac.za/science/meerkat/">MeerKAT</a> telescope in South Africa’s arid and sparsely populated Karoo region is one of the world’s most powerful radio telescopes. It is also one of the precursor telescopes that have been built in preparation for an almighty radio telescope called the <a href="https://www.skatelescope.org/">Square Kilometre Array</a> (SKA).</p>
<p>The SKA is an international mega-science project. Part of it will be built in South Africa and will incorporate MeerKAT. The other part will be built in Western Australia. Construction of the SKA is expected to begin this year.</p>
<p>Through these and other projects, Africa is beginning to emerge as a world leader in astronomy. Many brilliant scientists contribute to this status – but without one, Dr Bernie Fanaroff, the SKA might never have come to South African shores. </p>
<p>We are both astronomers and, in March 2019 launched a podcast, <a href="https://thecosmicsavannah.com/">The Cosmic Savannah</a>, to showcase the amazing astronomy and astrophysics coming out of the African continent. When we reached the 50th episode, Bernie was the obvious guest for the landmark occasion.</p>
<p>Who better than Bernie, we thought, to reflect on how the discipline reached this point.</p>
<p><audio preload="metadata" controls="controls" data-duration="3182" data-image="" data-title="Episode 50: Titans of Astronomy" data-size="127308502" data-source="The Cosmic Savannah" data-source-url="https://thecosmicsavannah.com/episode-50-titans-of-astronomy/" data-license="CC BY-NC-ND" data-license-url="http://creativecommons.org/licenses/by-nc-nd/4.0/">
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Episode 50: Titans of Astronomy.
<span class="attribution"><a class="source" rel="nofollow" href="https://thecosmicsavannah.com/episode-50-titans-of-astronomy/">The Cosmic Savannah</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a><span class="download"><span>121 MB</span> <a target="_blank" href="https://cdn.theconversation.com/audio/2496/050-the-cosmic-savannah-titans-of-astronomy.mp3">(download)</a></span></span>
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<h2>Globally famous</h2>
<p>Fanaroff is one of the key individuals responsible for the current growth and strength of astronomy in South Africa. He is a world-renowned radio astronomer who, while working on his PhD at Cambridge University in the early 1970s, made a breakthrough <a href="https://ui.adsabs.harvard.edu/abs/1974MNRAS.167P..31F/abstract">discovery</a> about radio galaxies. Radio galaxies contain supermassive black holes at their cores which spew out huge jets of plasma and glow at radio wavelengths.</p>
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Read more:
<a href="https://theconversation.com/discovery-of-two-new-giant-radio-galaxies-offers-fresh-insights-into-the-universe-153457">Discovery of two new giant radio galaxies offers fresh insights into the universe</a>
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<p>Bernie and his collaborator, a British astronomer named Julia Riley, were some of the first people to examine high-resolution images of such radio galaxies. They noticed that the luminosity of a radio galaxy was closely related to the shape of the plasma jets. This led to what became known as the “<a href="https://ned.ipac.caltech.edu/level5/Glossary/Essay_fanaroff.html">Fanaroff-Riley</a>” classification system, still used today, in which galaxies are grouped by their “Fanaroff-Riley” type.</p>
<p>But it took decades for Fanaroff to learn that a classification system had been named partly in his honour. He left the field of astronomy shortly after completing his PhD. Incensed by the poor treatment of workers in apartheid South Africa, he joined the National Union of Metalworkers, eventually becoming its national secretary. He later served in Nelson Mandela’s government, beginning in 1994.</p>
<p>Come 2003, he attended an astronomy conference – and discovered he was world famous. He told us:</p>
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<p>One or two people said to me, ‘Are you the Fanaroff of Fanaroff-Riley?’ This was actually news to me. And they said, ‘We thought you were dead! We heard you’d died because nobody’s heard anything of you since, you know, 1974.’ So I said, ‘No, I haven’t died and it is me,’ but it was all a bit of a surprise.</p>
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<p>After this, Fanaroff returned to astronomy: he became the project director for South Africa’s bid to host the Square Kilometre Array Telescope. Both South Africa and Australia were finalists in the bid; in 2012 it was decided by the international SKA consortium that the telescope would be split between both sites.</p>
<h2>A long-term vision</h2>
<p>Fanaroff and his colleague, Professor Justin Jonas, drove the bid. In our interview, he recalled:</p>
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<p>So [Jonas] said, if we’re going to have the world’s largest telescope in South Africa and in Africa, we better develop a community of radio astronomers and engineers who can build it and use it. So we were able to persuade our steering committee that we should start building a precursor.</p>
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<img alt="" src="https://images.theconversation.com/files/463690/original/file-20220517-20-qzsjhd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/463690/original/file-20220517-20-qzsjhd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/463690/original/file-20220517-20-qzsjhd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/463690/original/file-20220517-20-qzsjhd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/463690/original/file-20220517-20-qzsjhd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/463690/original/file-20220517-20-qzsjhd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/463690/original/file-20220517-20-qzsjhd.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">
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<span class="caption">Some of the dishes that make up the MeerKAT, a precursor to the SKA, in South Africa’s Karoo region.</span>
<span class="attribution"><span class="source">Mujahid Safodien/AFP via Getty Images</span></span>
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<p>The project quickly became about more than just science: it also drove human capacity development in South African astronomy. At the time of the SKA bid there were only five or six radio astronomers in the country.</p>
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Read more:
<a href="https://theconversation.com/how-the-ska-telescope-is-boosting-south-africas-knowledge-economy-96228">How the SKA telescope is boosting South Africa's knowledge economy</a>
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<p>He explained: </p>
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<p>“We decided very early on that we had to focus on getting the young people into science and making sure that we could develop them. So we put aside money for grants for undergraduate study in physics and engineering, for postgraduate study, for masters and PhD students, for research fellows.”</p>
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<p>Ultimately, it was this long-term vision which led to Bernie and his team landing the biggest global scientific project in Africa.</p>
<h2>A bright age of astronomy</h2>
<p>Thanks to people like Bernie, the future is bright for African astronomy. His message to young researchers, he said on the podcast, is: </p>
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<p>I think that you’re actually in a golden age of astronomy and I really envy you and the other young people who are coming into astronomy. Now you’ve got the MeerKAT, but you’ll soon have the SKA, which will be a wonderful telescope.</p>
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<p>He added: “You’ll have the (<a href="https://www.jwst.nasa.gov/">James Webb Space Telescope</a>), which will be a revolutionary optical and infrared telescope. You’ve got all the other new telescopes, the <a href="https://elt.eso.org/">Extremely Large Telescope</a> (in Chile), gamma-ray telescopes. And of course, you’ve now got gravitational wave telescopes. So you’re in a golden age where you’re going to be having so many opportunities.”</p><img src="https://counter.theconversation.com/content/183248/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daniel Cunnama receives funding from the National Research Foundation. He is affiliated with the South African Astronomical Observatory</span></em></p><p class="fine-print"><em><span>Jacinta Delhaize received funding from the NRF for a South African Radio Astronomy postdoctoral fellowship 2018-2021.</span></em></p>Fanaroff is one of the key individuals responsible for the current growth and strength of astronomy in South Africa.Daniel Cunnama, Science Engagement Astronomer, South African Astronomical Observatory, South African Astronomical ObservatoryJacinta Delhaize, Lecturer, University of Cape TownLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1707532021-10-29T04:46:36Z2021-10-29T04:46:36Z60 years after it first gazed at the skies, the Parkes dish is still making breakthroughs<figure><img src="https://images.theconversation.com/files/429275/original/file-20211029-15-198o6ab.jpeg?ixlib=rb-1.1.0&rect=9%2C671%2C6479%2C5136&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">CSIRO</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The CSIRO’s 64-metre Parkes Radio Telescope was commissioned on October 31 1961. At the time it was the most advanced radio telescope in the world, incorporating many innovative features that have since become standard in all large-dish antennas. </p>
<p>Through its early discoveries it quickly became the leading instrument of its kind. Today, 60 years later, it is still arguably the finest single-dish radio telescope in the world. It is still performing world-class science and making discoveries that shape our understanding of the Universe.</p>
<p>The telescope’s origins date back to wartime radar research by the Radiophysics Laboratory, part of the Council for Scientific and Industrial Research (CSIR), the forerunner of the CSIRO. On the Sydney clifftops at Dover Heights, the laboratory developed radar for use in the Pacific theatre. When the second world war ended, the technology was redirected into peaceful applications, including studying radio waves from the Sun and beyond.</p>
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<img alt="Researchers use the antenna at Dover Heights" src="https://images.theconversation.com/files/429271/original/file-20211029-18-gtm4qf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429271/original/file-20211029-18-gtm4qf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=601&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429271/original/file-20211029-18-gtm4qf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=601&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429271/original/file-20211029-18-gtm4qf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=601&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429271/original/file-20211029-18-gtm4qf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=755&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429271/original/file-20211029-18-gtm4qf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=755&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429271/original/file-20211029-18-gtm4qf.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">
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<span class="caption">Early antennas were much simpler, not to mention smaller.</span>
<span class="attribution"><span class="source">CSIRO</span>, <span class="license">Author provided</span></span>
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<p>In 1946, British physicist Edward “Taffy” Bowen was appointed chief of the Radiophysics Laboratory. He had been one of the brilliant engineers, dubbed “boffins”, who developed radar as part of Britain’s secret prewar military research. The Radiophysics Laboratory had a dedicated radio astronomy group, led by the brilliant Joseph (Joe) Pawsey. Many of the group’s members went on to become leaders in the nascent field of radio astronomy, including Bernie Mills, Chris Christiansen, Paul Wild, Ruby Payne-Scott (the first female radio astronomer), and John Bolton.</p>
<p>While the group’s initial research focused on radio waves from the Sun, Bolton’s attention soon shifted to identifying other sources from farther afield. By the early 1950s, the Dover Heights radar dishes had discovered more than 100 sources of radio emissions from the Milky Way and beyond, including the signals from supernova explosions. These observations established the Radiophysics Laboratory as a world-leading centre of radio astronomy.</p>
<p>By 1954, the technology at Dover Heights was outdated and obsolete, prompting Bowen to initiate the next step for Australian radio astronomy: a state-of-the-art new radio telescope.</p>
<p>He decided the most versatile option was to build a large, fully steerable dish antenna. The eventual price tag was A$1.4 million (A$25.6 million in today’s terms) – far beyond CSIRO’s budget at the time.</p>
<p>The Menzies government agreed to fund the project, provided at least 50% of the money came from the private sector. Using his wartime contacts, Bowen secured A$250,000 each from the Carnegie Corporation and Rockefeller Foundation, plus a range of private Australian donations.</p>
<p>British firm Freeman Fox and Partners produced the detailed design, incorporating suggestions from legendary engineer Barnes Wallis, of “dambusters” fame. Based on the available budget and desired functionality, a diameter of 64 metres was agreed for the dish.</p>
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<a href="https://images.theconversation.com/files/429264/original/file-20211029-23-nnz6hy.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="1955 design by Barnes Wallis" src="https://images.theconversation.com/files/429264/original/file-20211029-23-nnz6hy.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429264/original/file-20211029-23-nnz6hy.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=662&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429264/original/file-20211029-23-nnz6hy.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=662&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429264/original/file-20211029-23-nnz6hy.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=662&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429264/original/file-20211029-23-nnz6hy.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=832&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429264/original/file-20211029-23-nnz6hy.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=832&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429264/original/file-20211029-23-nnz6hy.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=832&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">1955 design notes by Barnes Wallis.</span>
<span class="attribution"><span class="source">CSIRO</span>, <span class="license">Author provided</span></span>
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<p>The chosen site was near the town of Parkes, about 350km west of Sydney. This location had favourable weather conditions and was free of local radio interference. The local council also enthusiastically offered to cover the cost of some of the earthworks.</p>
<p>In 2020, the local Wiradjuri people <a href="https://blog.csiro.au/parkes-telescope-indigenous-name/">named the telescope Murriyang</a>, a traditional name meaning “Skyworld”.</p>
<p>The telescope’s construction began in September 1959 and was completed just two years later. On October 31 1961, the Governor-General William Sidney, Viscount De l'Isle, officially opened the telescope in a ceremony attended by 500 guests.</p>
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<img alt="The Parkes dish's opening ceremony" src="https://images.theconversation.com/files/429278/original/file-20211029-26-91kgrk.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429278/original/file-20211029-26-91kgrk.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=595&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429278/original/file-20211029-26-91kgrk.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=595&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429278/original/file-20211029-26-91kgrk.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=595&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429278/original/file-20211029-26-91kgrk.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=748&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429278/original/file-20211029-26-91kgrk.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=748&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429278/original/file-20211029-26-91kgrk.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=748&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 Governor-General (centre) greets guests at the telescope’s 1961 opening ceremony.</span>
<span class="attribution"><span class="source">CSIRO</span>, <span class="license">Author provided</span></span>
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<h2>Decades of discovery</h2>
<p>John Bolton was appointed the founding director of the telescope. Under his dynamic, decade-long tenure, astronomers made a string of significant discoveries that established the dish as the premier scientific instrument in Australia. </p>
<p>Astronomers revealed the immense magnetic field of our Milky Way galaxy. A few months later, the telescope detected quasars, the most distant known objects in the Universe – a discovery that increased the size of the known Universe tenfold. To cap off a memorable first year, Parkes tracked the very first interplanetary space mission, Mariner 2, when it flew past Venus in December 1962.</p>
<p>In the 1970s, researchers discovered and mapped the immense molecular clouds interspersed through our galaxy. The study of pulsars – rotating stars that emit beams of radio waves, rather like a lighthouse – became a major field of research. Parkes has discovered more pulsars than all other radio observatories combined, including the only known double pulsar system, spotted in 2003. </p>
<p>In the 1990s, the distribution of galaxies was mapped to a distance of 300 million light years, revealing the complex structure of the Universe. More recently, Parkes discovered the first Fast Radio Burst – a short, intense <a href="https://theconversation.com/a-brief-history-what-we-know-so-far-about-fast-radio-bursts-across-the-universe-154381">blast of radio waves</a> created by an as-yet unknown process. The telescope has also been involved in the Search for Extra-Terrestrial Intelligence (SETI), including the ten-year <a href="https://breakthroughinitiatives.org/initiative/1">Breakthrough Listen project</a>, which began in 2016.</p>
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Read more:
<a href="https://theconversation.com/a-brief-history-what-we-know-so-far-about-fast-radio-bursts-across-the-universe-154381">A brief history: what we know so far about fast radio bursts across the universe</a>
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<p>To the public, the telescope is perhaps best known for its space tracking, especially its role in the Apollo lunar missions. But it has also supported other significant missions such as NASA’s <a href="https://theconversation.com/australia-is-still-listening-to-voyager-2-as-nasa-confirms-the-probe-is-now-in-interstellar-space-108507">Voyager 2</a>, which flew past Uranus and Neptune in the 1980s and crossed into interstellar space in 2018. In 1986, Parkes was the prime tracking station for the European Giotto mission to Halley’s Comet. And next year, Parkes will track some of the first commercial lunar landers.</p>
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Read more:
<a href="https://theconversation.com/australia-is-still-listening-to-voyager-2-as-nasa-confirms-the-probe-is-now-in-interstellar-space-108507">Australia is still listening to Voyager 2 as NASA confirms the probe is now in interstellar space</a>
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<img alt="Parkes dish with the Moon in the background." src="https://images.theconversation.com/files/429268/original/file-20211029-19-1e2zq5n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429268/original/file-20211029-19-1e2zq5n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=749&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429268/original/file-20211029-19-1e2zq5n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=749&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429268/original/file-20211029-19-1e2zq5n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=749&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429268/original/file-20211029-19-1e2zq5n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=941&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429268/original/file-20211029-19-1e2zq5n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=941&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429268/original/file-20211029-19-1e2zq5n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=941&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">Parkes tracking the Apollo Moon mission in 1969.</span>
<span class="attribution"><span class="source">CSIRO</span>, <span class="license">Author provided</span></span>
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<p>Originally intended to operate for 20 years, the telscope’s longevity is a result of constant upgrades. Recent improvements include a new ultra-wideband receiver that can scan a huge range of radio frequencies, and CSIRO-developed “phased array feeds” (PAFs) that allow the telescope to observe up to 36 points in the sky at once. Work is now under way on a cryogenically cooled PAF that, when installed in 2022, will double this number. With these upgrades in place, a single receiver can be used to deliver more than 90% of current Parkes operations.</p>
<figure class="align-center ">
<img alt="Construction workers building the dish" src="https://images.theconversation.com/files/429273/original/file-20211029-25-1ocnr6f.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/429273/original/file-20211029-25-1ocnr6f.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=570&fit=crop&dpr=1 600w, https://images.theconversation.com/files/429273/original/file-20211029-25-1ocnr6f.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=570&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/429273/original/file-20211029-25-1ocnr6f.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=570&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/429273/original/file-20211029-25-1ocnr6f.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=716&fit=crop&dpr=1 754w, https://images.theconversation.com/files/429273/original/file-20211029-25-1ocnr6f.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=716&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/429273/original/file-20211029-25-1ocnr6f.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=716&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Construction took just two years.</span>
<span class="attribution"><span class="source">CSIRO</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>It’s hard to say how long the Parkes dish will continue to work. It depends on future upgrades and whether the telescope’s structure remains in good working order. But astronomers will always have a need for a large single-dish antenna.</p>
<p>Parkes has maintained its world-leading position in radio astronomy by constantly adapting to meet new requirements. Today it stands as an icon of Australian science and achievement. Sixty years after it first trained its eye on the sky, the future still looks bright at Parkes.</p><img src="https://counter.theconversation.com/content/170753/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Sarkissian does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>After six decades during which it tracked lunar missions, spotted distant pulsars and quasars, and even expanded our concept of the size of the Universe, the Parkes telescope is still going strong.John Sarkissian, Operations Scientist, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1375722020-05-13T11:40:08Z2020-05-13T11:40:08ZSpace junk: Astronomers worry as private companies push ahead with satellite launches<figure><img src="https://images.theconversation.com/files/334631/original/file-20200513-156641-95sq2q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Space junk is making low Earth orbit crowded.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/space-junk-orbiting-around-earth-conceptual-233084350">Johan Swanepoel/Shuttertock</a></span></figcaption></figure><p>Since the launch of Sputnik 1 in 1957, the lower orbit around the Earth has become an increasingly congested environment with more than 2,200 satellite launches to date. Those satellites – along with launch vehicle components and debris from mechanical disintegration, collisions and explosions – now fill this region with a “fog” of space debris.</p>
<hr>
<iframe id="noa-web-audio-player" style="border: none" src="https://embed-player.newsoveraudio.com/v4?key=x84olp&id=https://theconversation.com/space-junk-astronomers-worry-as-private-companies-push-ahead-with-satellite-launches-137572&bgColor=F5F5F5&color=D8352A&playColor=D8352A" width="100%" height="110px"></iframe>
<p><em>You can listen to more article from The Conversation, narrated by Noa, <a href="https://theconversation.com/uk/topics/audio-narrated-99682">here</a>.</em> </p>
<hr>
<p>And it’s getting busier. In the last few weeks, SpaceX <a href="https://www.space.com/space-starlink-satellites-launch-rocket-landing-success-april-2020.html">has launched 60 new satellites</a> as part of its Starlink programme. This brings the total to currently around 400 Starlink satellites in low Earth orbit as part of a programme that aims to bring cheap, satellite-based internet access to everyone. Eventually, this programme could place nearly 12,000 satellites in orbit around the Earth.</p>
<p>With Amazon, Canada’s <a href="https://www.telesat.com/services/leo/phase-1">Telesat</a> and others <a href="https://www.cnbc.com/2019/12/14/spacex-oneweb-and-amazon-to-launch-thousands-more-satellites-in-2020s.html">planning satellite constellations</a> of similar scale, low Earth orbit is becoming ever more crowded. </p>
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<p>The debris ranges in size from a few microns to many metres. <a href="https://www.stugrey.com/">Stuart Grey</a>, an aerospace engineer at the University of Strathclyde, has produced a stunning visualisation that highlights the more than 20,000 objects over 10cm in size now orbiting the Earth (see video above). But there are many millions of particles 1mm in size and smaller.</p>
<h2>Closing our window on the universe?</h2>
<p>Amateur astronomers are <a href="https://edition.cnn.com/2020/04/21/tech/starlink-satellites-stargazers-complaints-scli-intl-gbr/index.html">already expressing concern</a> over the increasing number of bright, moving objects in the night sky. But the worry is perhaps much greater for the professionals.</p>
<p>Crowding in low Earth orbit has inevitable consequences for ground-based astronomers. Bright surfaces on satellites can reflect rays from the sun – giving rise to a burst of sunlight directed towards the surface of the Earth. Such intense bursts of light are much stronger than the weak light sources typically being observed by astronomers and will impede observations of distant objects in space. </p>
<p>Billions have already been spent on existing optical telescopes, and many more billions will be poured into new platforms in the next decade, such as the <a href="https://www.eso.org/sci/facilities/eelt/">European Extremely Large Telescope</a> being built on the Atacama plateau in Chile. There is intense competition for observing time on such resources, so any potential threat from satellite reflections must be taken seriously as they may make some of the observations driving our understanding of the evolution of the universe impossible.</p>
<p>SpaceX has assured the public that Starlink will not contribute to this problem and says it <a href="https://time.com/5225670/spacex-space-junk-cleaner-launch/">has been taking steps</a> to mitigate the impacts of its satellites on observational astronomy – even to the extent of testing whether a black coating on its satellites can reduce visibility, and adjusting some of the satellites’ orbits if necessary.</p>
<p>With some 3% of its planned constellation launched, SpaceX is at least responding to the concerns raised by astronomers. Hopefully other agencies planning satellite constellation launches will also be upfront with their plans to reduce this serious problem to astronomical observation.</p>
<p>But crowding in low Earth orbit also has consequences for satellites and other space vehicles, including those designed to carry humans. To achieve orbit, satellites seek a balance between their speed and the effect of Earth’s gravity on them. The speed with which a satellite must travel to achieve this balance depends on its altitude above Earth. The nearer to Earth, then the faster the required orbital speed. </p>
<p>At an altitude of 124 miles (200km), the required orbital velocity is a little more than 17,000 miles per hour (about 7.4 km/s). Any object shed by a satellite or other vehicle in orbit will maintain the same orbital speed. Collisions between such objects can therefore occur at combined speeds of potentially up to 34,000 mph at 124 miles (if it is head-on). The effects of such impacts can be serious for astronauts and space stations – as the dramatic opening scenes of the 2013 movie Gravity depict. </p>
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<p>There is impact shielding on satellites and space vehicles which is designed to stop objects smaller than 1cm crashing into them. At best, the shielding will do so – though the electromagnetic impulse created may interfere with electronic systems. At worst, larger pieces of space junk could penetrate the vehicles. This could result in internal damage and disintegration that threaten the safety of the mission.</p>
<p>Space agencies such as NASA and ESA have therefore established <a href="https://www.orbitaldebris.jsc.nasa.gov/">orbital debris research programmes</a> to observe such debris and develop strategies to control its effects. </p>
<p>There is little doubt that, with the increasing use and commercialisation of space, we boost the risk of catastrophic events associated with orbital debris. Agencies, both state and commercial, must recognise this and support efforts to reduce the likelihood of such events by taking steps to remove existing debris and reduce the potential for further debris by removing redundant satellites and other space vehicles. For example the <a href="https://www.surrey.ac.uk/news/harpoon-successfully-captures-space-debris">RemoveDEBRIS satellite</a> uses an on-board harpoon to capture junk.</p>
<p>Only when we resolve the problem of space junk will our window on, and pathway to, space be truly fully open.</p><img src="https://counter.theconversation.com/content/137572/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Martin McCoustra does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>SpaceX recently launched 60 satellites into orbit around Earth as part of its Starlink programme.Martin McCoustra, ScotCHEM Chair in Chemical Physics, Heriot-Watt UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/784592017-05-31T04:53:33Z2017-05-31T04:53:33ZJuno mission unveils Jupiter’s complex interior, weather and magnetism<figure><img src="https://images.theconversation.com/files/171379/original/file-20170530-25261-1tkieiz.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This enhanced-color image of Jupiter’s south pole and its swirling atmosphere was created by citizen scientist Roman Tkachenko using data from the JunoCam imager on NASA’s Juno spacecraft.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/jpl/pia21381/jupiter-from-below-enhanced-color">NASA/JPL-Caltech/SwRI/MSSS/Roman Tkachenko</a></span></figcaption></figure><p>The latest observations of the <a href="https://www.nasa.gov/mission_pages/juno/main/index.html">Juno spacecraft</a> are helping astronomers uncover the true nature of Jupiter in unprecedented detail. Many of the findings were unexpected.</p>
<p>Since July 2016, Juno has been revolving around Jupiter – the largest planet in our Solar System – in a highly elongated, 53-day orbit. This allows a clear view of its poles while the spacecraft ducks in and out of the strong radiation regions that surround the planet. </p>
<p>The first results of Juno observations were released in <a href="http://science.sciencemag.org/content/356/6340/821">two</a> <a href="http://science.sciencemag.org/content/356/6340/826">studies</a> published in Science last week. They reveal a very new picture of the Jovian interior, its atmosphere and magnetosphere.</p>
<p>Of course it’s not only the observations from Juno that are helping us better understand Jupiter. Simultaneous monitoring from ground based telescopes such as the ones on Mauna Kea in Hawaii, where I was recently, are also helping.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/171555/original/file-20170531-23667-13tse61.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/171555/original/file-20170531-23667-13tse61.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171555/original/file-20170531-23667-13tse61.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=422&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171555/original/file-20170531-23667-13tse61.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=422&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171555/original/file-20170531-23667-13tse61.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=422&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171555/original/file-20170531-23667-13tse61.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=530&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171555/original/file-20170531-23667-13tse61.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=530&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171555/original/file-20170531-23667-13tse61.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=530&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Here I am on Mauna Kea in Hawaii.</span>
<span class="attribution"><span class="source">Marcel de Vriend</span></span>
</figcaption>
</figure>
<p>But first to the latest Juno discoveries.</p>
<h2>The atmosphere</h2>
<p>Juno’s multiple passes over polar regions of the planet revealed stunning images of swirling cyclones, some almost as large as Earth. </p>
<p>There is no banded structure visible in these images, in contrast to Jupiter’s equatorial regions. There is no hexagon or a central vortex in the southern polar region like the one that the <a href="https://www.nasa.gov/mission_pages/cassini/whycassini/cassini20130429.html">Cassini probe observed</a> in Saturn’s north polar atmosphere. </p>
<p>It also appears that a high-altitude thin cloud or a haze, of yet unknown composition, hovers over both poles of Jupiter. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/171418/original/file-20170530-16298-knsccb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/171418/original/file-20170530-16298-knsccb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171418/original/file-20170530-16298-knsccb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=468&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171418/original/file-20170530-16298-knsccb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=468&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171418/original/file-20170530-16298-knsccb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=468&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171418/original/file-20170530-16298-knsccb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=588&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171418/original/file-20170530-16298-knsccb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=588&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171418/original/file-20170530-16298-knsccb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=588&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Juno’s view of Jupiter’s south pole from an altitude of 52,000 kilometers. The oval features are cyclones, up to 1,000 kilometers in diameter.</span>
<span class="attribution"><a class="source" href="https://www.nasa.gov/press-release/a-whole-new-jupiter-first-science-results-from-nasa-s-juno-mission">NASA/JPL-Caltech/SwRI/MSSS/Betsy Asher Hall/Gervasio Robles</a></span>
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</figure>
<p>Juno’s radiometry measurements can probe the atmosphere to the unprecedented depth of 350km. This takes it below the frozen ammonia cloud top that we usually see in visible light images of the planet, with atmospheric pressures up to 240 times greater than on Earth’s surface.</p>
<p>Astronomers have already studied the rich and dynamic Jovian weather system since the first space observations of its atmospheric composition and profiles from the <a href="https://voyager.jpl.nasa.gov/">Voyager probes</a>. But the previous deepest atmospheric measurements could be considered skin-deep when compared with Juno’s latest observations. </p>
<p>Only in one specific area of the planet was the atmosphere studied up to a depth of 100km. That was in 1995, when the Galileo probe descended into a so-called “hot spot”, a dark region between ammonia clouds that glows strongly in infrared light. Galileo’s probe measurements found this region surprisingly devoid of any water vapour clouds, as would have been expected below ammonia cloud. </p>
<p>Now, for the first time Juno’s radiometry allows a global view of deep atmosphere, showing that the banded pattern extends deeply below the visible tops of the clouds. </p>
<p>The measurements of ammonia content in these deep layers reveals an unexpected and dynamic mixing similar to the <a href="https://www.britannica.com/science/Hadley-cell">Hadley cells</a> in Earth’s atmosphere. This is where masses of hot air rise in equatorial regions and move polewards, before plummeting in the tropics and returning towards the Equator close to Earth’s surface.</p>
<p>One of the goals of the Juno mission was to measure water content in the Jovian atmosphere, which has implications for understanding Solar System formation.</p>
<p>So far Juno has confirmed that the hot spots are indeed very dry regions of descending air with humidity less than 10%.</p>
<h2>The magnetosphere</h2>
<p>Since the <a href="https://radiojove.gsfc.nasa.gov/library/sci_briefs/discovery.html">discovery of strong radio emission from Jupiter</a> in the 1950s – implying the existence of a magnetic field around the planet – every new space mission has slowly added to the ever so complex picture of the Jovian magnetosphere.</p>
<p>The Juno mission is designed to make an unprecedented leap forward in the understanding magnetic field generation processes and also to make a detailed map of the planet’s magnetosphere. </p>
<p>One of the most spectacular consequences of interaction between the magnetosphere and atmosphere of a planet is an auroral display, similar to the northern and southern lights on Earth. </p>
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<figcaption><span class="caption">Jupiter’s ‘southern lights’ as captured by Juno. (NASA/JPL-Caltech/SWRI)</span></figcaption>
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<p>The <a href="https://www.missionjuno.swri.edu/spacecraft/juno-spacecraft/">JADE, JEDI and Waves instruments</a> placed on Juno are used to measure the energies of particles that plummet into the polar regions and smash into atmospheric gases, mainly hydrogen that emits radiation, which we see as aurora.</p>
<p>The ultraviolet and infrared maps of this emission allow us to measure how the top layers of the Jovian atmosphere heat up and cool, as well as to understand the dynamics of the magnetosphere. </p>
<p>But why is the <a href="https://www.missionjuno.swri.edu/media-gallery/magnetosphere">magnetosphere</a> worth our attention? Planetary magnetospheres act like protective shields that deflect space radiation harmful to life.</p>
<p>Only planets that can produce magnetic fields have magnetospheres and, lucky for us, Earth has one too. But besides Earth, only the giant planets in our Solar System have appreciable magnetospheres. </p>
<p>Juno measured magnetic field in regions closer to Jupiter than ever before, and the results were very different than the predictions from the previously used models. </p>
<p>The observed magnetic fields are stronger and also more spatially variable than previously assumed. Since it is understood that a magnetic field is formed in the cores of planets via dynamo process, this suggests that magnetic field formation region is actually much larger than expected. </p>
<p>This, in turn, in combination with Juno’s measurements of gravitational field around the planet, tells us that our previous ideas about the core of the planet may have to be revised. </p>
<p>For example, the textbook images of the rather compact core of metallic hydrogen is not consistent with Juno observations. The metallic hydrogen core could be as large as the half of Jupiter’s radius.</p>
<h2>Back on Earth</h2>
<p>During Juno’s closest approach to Jupiter – while the probe makes critical observations of Jovian weather, magnetism and gravity – some of the largest telescopes on Earth support the mission with imaging and spectroscopy of the giant planet.</p>
<p>Although the spatial resolution of such observations is no match for imaging from Juno, ground telescopes have a global view of the planet. </p>
<p>During the sixth approach of Juno to the planet on May 19, some of us were using telescopes on Mauna Kea in Hawaii.</p>
<p>I used a high-resolution infrared spectroscope at the Gemini telescope to map the full extend of auroral hydrogen emission around both planetary poles, while my colleagues were taking infrared images of the same regions at the Subaru telescope. </p>
<p>It is exciting to participate in this critical ground base support of the Juno mission, when the international astronomical community joins for a once in a lifetime opportunity to get a very unique view of our giant neighbour.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/171556/original/file-20170531-23699-1xyn62j.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/171556/original/file-20170531-23699-1xyn62j.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171556/original/file-20170531-23699-1xyn62j.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171556/original/file-20170531-23699-1xyn62j.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171556/original/file-20170531-23699-1xyn62j.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171556/original/file-20170531-23699-1xyn62j.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171556/original/file-20170531-23699-1xyn62j.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171556/original/file-20170531-23699-1xyn62j.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">Here I am in front of the terminals to the Gemini Telescope, in Hawaii.</span>
<span class="attribution"><span class="source">Jen Miller</span></span>
</figcaption>
</figure>
<p>It is also amazing to have a support from many amateur astronomy groups that joined in observations of visible light from the planet.</p>
<p>The raw images from the Juno’s visible light camera are available on the <a href="https://www.nasa.gov/mission_pages/juno/main/index.html">Juno website</a> for public use. People are invited to process such images and submit their work for viewing.</p>
<h2>Future goals for Juno</h2>
<p>Juno’s unique orbit allows for making spectacular images of regions not visited in previous missions. The probe also comes much better equipped than some of its predecessors to visit the planet. </p>
<p>The first results from the mission are already suggesting future revisions, or at least adjustments to models of Jupiter’s atmosphere, interior and magnetism. </p>
<p>This unique study of our largest giant planet will hopefully bear implications on the understanding of the formation and composition of similar but much hotter giant planets discovered around other stars.</p><img src="https://counter.theconversation.com/content/78459/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lucyna Kedziora-Chudczer does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>We may need to re-think our models of Jupiter’s formation thanks to the first results from Juno probe orbiting the planet, and new observations from Earth.Lucyna Kedziora-Chudczer, Postdoctoral Fellow, Astrophysics Researcher, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/499272016-01-15T11:14:14Z2016-01-15T11:14:14ZHow do you build a mirror for one of the world’s biggest telescopes?<figure><img src="https://images.theconversation.com/files/106709/original/image-20151218-27894-sl57k3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">20 tons of Ohara E6 borosilicate glass being loaded onto the mold of one of the GMT's mirrors.</span> <span class="attribution"><span class="source">Ray Bertram, Steward Observatory</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>When astronomers point their telescopes up at the sky to see distant supernovae or quasars, they’re collecting light that’s traveled millions or even billions of light-years through space. Even huge and powerful energy sources in the cosmos are unimaginably tiny and faint when we view them from such a distance. In order to learn about galaxies as they were forming soon after the Big Bang, and about nearby but much smaller and fainter objects, astronomers need more powerful telescopes. </p>
<p>Perhaps the poster child for programs that require extraordinary sensitivity and the sharpest possible images is the <a href="http://www.seti.org/seti-institute/weeky-lecture/beyond-kepler-direct-imaging-earth-planets">search for planets around other stars</a>, where the body we’re trying to detect is extremely close to its star and roughly a billion times fainter. Finding earth-like planets is one of the most exciting prospects for the next generation of telescopes, and could eventually lead to discovering extraterrestrial signatures of life.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/107834/original/image-20160111-6968-4vj025.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/107834/original/image-20160111-6968-4vj025.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/107834/original/image-20160111-6968-4vj025.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/107834/original/image-20160111-6968-4vj025.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/107834/original/image-20160111-6968-4vj025.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/107834/original/image-20160111-6968-4vj025.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/107834/original/image-20160111-6968-4vj025.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/107834/original/image-20160111-6968-4vj025.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"></a>
<figcaption>
<span class="caption">Size comparison of optical telescopes’ primary mirrors.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Comparison_optical_telescope_primary_mirrors.svg">Cmglee</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Detectors in research telescopes are already so sensitive that they capture almost every incoming photon, so there’s only one way to detect fainter objects and resolve structure on finer scales: build a bigger telescope. A large telescope doesn’t just capture more photons, it can also produce sharper images. That’s because the wave nature of light sets a limit to the telescope’s resolution, known as the <a href="http://www.astro.cornell.edu/academics/courses/astro201/diff_limit.htm">diffraction limit</a>; the sharpness of the image depends on the wavelength of the light and the telescope’s diameter.</p>
<p>As optical scientists, our contribution to the next generation of telescopes is figuring out how to craft the gargantuan mirrors they rely on to collect light from far away. Here’s how we’re perfecting the technology that will enable tomorrow’s astrophysical discoveries.</p>
<h2>Multiple mirrors</h2>
<p>The question is how to build something substantially bigger than the current generation of telescopes, which have effective diameters of 8 to 12 meters (26 to 40 feet). One of the biggest challenges is making a bigger mirror to collect the light.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/107958/original/image-20160112-6964-mpe02.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/107958/original/image-20160112-6964-mpe02.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/107958/original/image-20160112-6964-mpe02.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=566&fit=crop&dpr=1 600w, https://images.theconversation.com/files/107958/original/image-20160112-6964-mpe02.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=566&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/107958/original/image-20160112-6964-mpe02.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=566&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/107958/original/image-20160112-6964-mpe02.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=711&fit=crop&dpr=1 754w, https://images.theconversation.com/files/107958/original/image-20160112-6964-mpe02.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=711&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/107958/original/image-20160112-6964-mpe02.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=711&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Optical diagram of the Giant Magellan Telescope.</span>
<span class="attribution"><span class="source">Giant Magellan Telescope - GMTO Corporation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>First, it helps to know the basic optical layout of a telescope, illustrated here by the Giant Magellan Telescope (<a href="http://www.gmto.org/overview/">GMT</a>) that is being built in Chile. A large <em>primary mirror</em> collects incoming light and reflects it to a focus. The light is reflected a second time by the smaller <em>secondary mirror</em>, to form an image on an instrument located at a safe, accessible place below the primary mirror, where the image is recorded.</p>
<p>A mirror much larger than eight meters, made of a single piece of glass, would be too expensive and too hard to handle. Everyone involved in building giant telescopes agrees that the solution is to make the primary mirror out of multiple smaller mirrors. Multiple pieces of glass are shaped and aligned to form one gigantic mirror, called a segmented mirror. Gaps between the segments are acceptable as long as the segments’ surfaces lie on a continuous nearly parabolic surface, called the parent surface. </p>
<p>The three extremely large telescope (ELT) projects now in development have made very different decisions about the design of this segmented primary mirror. Two of the ELTs, the <a href="http://www.eso.org/public/teles-instr/e-elt/e-elt_con/">European ELT</a> and the <a href="http://www.tmt.org/observatory">Thirty Meter Telescope</a>, have adopted the approach pioneered by the <a href="http://www.keckobservatory.org">10-meter Keck Observatory telescopes</a> in Hawaii – they’ll make a giant mirror out of hundreds of 1.5-meter segments.</p>
<p>The third project, the Giant Magellan Telescope, takes a different tack. Its 25-meter primary mirror will have only seven segments. They’re the largest single mirrors that can be made, the 8.4-meter (28-foot) honeycomb mirrors we produce here at the <a href="http://mirrorlab.as.arizona.edu">Richard F. Caris Mirror Lab</a> at the University of Arizona. The GMT’s 3-meter secondary mirror also has seven segments, each paired with one of the primary mirror segments.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/107310/original/image-20160105-28991-1bp389o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/107310/original/image-20160105-28991-1bp389o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/107310/original/image-20160105-28991-1bp389o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/107310/original/image-20160105-28991-1bp389o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/107310/original/image-20160105-28991-1bp389o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/107310/original/image-20160105-28991-1bp389o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/107310/original/image-20160105-28991-1bp389o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/107310/original/image-20160105-28991-1bp389o.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">Artist’s representation of the seven giant mirrors installed in the Giant Magellan Telescope.</span>
<span class="attribution"><a class="source" href="http://www.gmto.org/gallery/">Giant Magellan Telescope – GMTO Corporation</a></span>
</figcaption>
</figure>
<h2>Large, stiff and light</h2>
<p>Big mirror segments guarantee a smooth surface over their entire large areas. The more segments there are in the primary mirror, the more its accuracy depends on their precise alignment to keep them on the parent surface. Because of the pairing of primary and secondary mirror segments in the GMT, the fine control needed to form sharp images can be done by moving the small, agile segments of the secondary mirror rather than the 8.4-meter primary segments. A second advantage of the 8.4-meter honeycomb mirrors is their strong legacy, including use in what is currently the world’s largest telescope, the <a href="http://www.lbto.org/overview.html">Large Binocular Telescope</a> here in Arizona.</p>
<p>One of the challenges of using a large mirror is that it tends to bend under its own weight and the force of wind. The mirror is exposed to wind like a sail on a yacht, but it can only bend by about 100 nanometers before its images become too blurry. The best way to overcome this problem is to make the mirror as stiff as is practical, while also limiting its weight.</p>
<p>We accomplish this feat by casting the mirror into a lightweight honeycomb structure. Each mirror has a continuous glass facesheet on top and an almost continuous backsheet, each about one inch thick. Holding the two sheets together is a honeycomb structure consisting of half-inch-thick ribs in a hexagonal pattern. Our honeycomb mirrors are 70 centimeters thick, making them stiff enough to withstand the forces of gravity and wind. But they’re 80 percent hollow and weigh about 16 tons each, light enough that they don’t bend significantly under their own weight.</p>
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<a href="https://images.theconversation.com/files/106706/original/image-20151218-27894-4doo4f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/106706/original/image-20151218-27894-4doo4f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/106706/original/image-20151218-27894-4doo4f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/106706/original/image-20151218-27894-4doo4f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/106706/original/image-20151218-27894-4doo4f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/106706/original/image-20151218-27894-4doo4f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/106706/original/image-20151218-27894-4doo4f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/106706/original/image-20151218-27894-4doo4f.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">Mold for casting an 8.4-meter honeycomb mirror for the GMT. The glass will melt around the hexagonal boxes to form the honeycomb.</span>
<span class="attribution"><span class="source">Ray Bertram, Steward Observatory</span></span>
</figcaption>
</figure>
<h2>Crafting the mirror</h2>
<p>We start by melting glass into a complex mold that’s the negative of the honeycomb mirror we want to end up with. While the glass is molten, the furnace spins at five revolutions per minute; the centrifugal force pushes the glass’ surface into the concave parabolic shape that can focus light from a distant star. Watch the video below to see the construction of the honeycomb mold and the spin-casting process.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/c-lBKuHqHk0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Spin-casting the honeycomb mirror.</span></figcaption>
</figure>
<p>The spin-cast mirror surface doesn’t yet have the optical quality needed to make sharp images. But spinning gives it the right overall curvature and saves our having to grind out 14 tons of glass from a flat surface – almost as much glass as is left in the finished mirror. </p>
<h2>Polishing the surface</h2>
<p>Next we need to polish the surface to an accuracy of a small fraction of the light’s wavelength, so it will form the sharpest images possible. The mirror surface has to match the ideal, nearly parabolic surface to about 25 nanometers – about 3 ten-thousandths of the width of a human hair. That’s really, really smooth; if the mirror were scaled up to the size of North America, the tallest mountain would be one inch high and the deepest canyon would be one inch low.</p>
<p>To guide our polishing, the first step is to create a superfine contour map of the mirror’s surface, with steps of less than 10 nanometers. As our “ruler,” we use red laser light; its divisions are the light’s wavelength – about 630 nanometers – and it can be read to about one hundredth of a division.</p>
<p>The measuring instrument illuminates the mirror surface, collects the reflected light, and compares the path lengths of the rays reflected by different locations on the mirror. A ray that reflects off a high spot will have a shorter path than a ray that hits a low spot. The instrument uses this information to construct the contour map of the mirror’s surface.</p>
<p>The basic principle of polishing is to rub the surface with a disk-shaped tool, removing glass selectively from the spots that are too high. A fine abrasive such as rouge (iron oxide) slowly removes glass, atom by atom, through mechanical and chemical processes.</p>
<p><em>Figuring</em> is removing glass explicitly from high spots identified in the contour map, for example by having the tool rub there longer. This is effective on scales larger than about 10 centimeters. <em>Smoothing</em> is what happens when you rub a stiff tool over a rough surface: the tool naturally sits on the high spots and removes more material there, even without any guidance from a contour map. This is effective on scales smaller than 10 centimeters. Both methods are more difficult when the mirror surface is aspheric, meaning its curvature changes from point to point, which is very much the case for the GMT segments.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/107217/original/image-20160104-28966-yf299h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/107217/original/image-20160104-28966-yf299h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/107217/original/image-20160104-28966-yf299h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/107217/original/image-20160104-28966-yf299h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/107217/original/image-20160104-28966-yf299h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/107217/original/image-20160104-28966-yf299h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/107217/original/image-20160104-28966-yf299h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/107217/original/image-20160104-28966-yf299h.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">An 8.4-meter mirror for the Large Synoptic Survey Telescope being polished at the Richard F. Caris Mirror Lab.</span>
<span class="attribution"><span class="source">Steward Observatory</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>We’ve developed several new polishing tools to address the challenges of polishing large mirrors for telescopes. One essential feature of any polishing tool is that it match the shape of the mirror surface to an accuracy of around 1 micron. The larger tool in the background is a <a href="http://doi.org/10.1364/AO.33.008094">complex electro-mechanical system</a> that changes the shape of a stiff aluminum disk as it moves over the surface, so it always matches the local curvature of the mirror.</p>
<p>The smaller tool in the foreground is much simpler. Similar to <a href="http://dx.doi.org/10.1038/457028a">Galileo’s reinvention of a carnival toy</a> as an astronomical telescope, our <a href="http://dx.doi.org/10.1364/OE.18.002242">new idea came from Silly Putty</a> – a non-Newtonian fluid that flows like a liquid over a long period of time but acts like a solid on short timescales. We <a href="http://dx.doi.org/10.1364/OE.18.022515">harness those intrinsic properties</a> to achieve both figuring and smoothing. </p>
<p>Our tool, containing Silly Putty enclosed by a thin rubber diaphragm, slowly moves over the surface of the mirror while simultaneously rapidly orbiting around itself. The Silly Putty is stiff over the quick period of the orbit, which smooths out small-scale irregularities in the mirror surface. Over the longer time it takes to move across the mirror, the Silly Putty flows easily, so the tool always matches the surface’s shape. As a result, it removes glass at a predictable rate and in a predictable pattern that doesn’t vary as it moves across the mirror.</p>
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<figcaption>
<span class="caption">The Giant Magellan Telescope as it will look after construction on Cerro Las Campanas in Chile.</span>
<span class="attribution"><a class="source" href="http://www.gmto.org/gallery/">Giant Magellan Telescope – GMTO Corporation</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Countdown to installation</h2>
<p>Here at the Mirror Lab, we finished making the first Giant Magellan Telescope segment in 2012. After a pause for work on two other mirrors, the lab is in the process of grinding Segments 2 and 3. Segment 4 has just finished cooling to room temperature after spin-casting in September 2015. We are well on the way to manufacturing the full 25-meter primary mirror. </p>
<p>Getting these near-perfect mirrors from our lab in Arizona to a mountaintop in Chile presents another set of challenges. They travel by tractor-trailer on land, and by freight ship from California to Chile. The keys to safe transport are distributing the weight of the mirror over hundreds of support points and having several layers of suspension between the mirror and the road or ship deck. </p>
<p>The GMT project schedule calls for a preliminary first light, with four segments installed in the telescope, in 2022. We expect all seven segments to be scanning the cosmos starting in 2024. </p>
<p>Many of us who work on the GMT see it as the way to open new windows into the universe, as the Hubble Space Telescope (HST) has done over the last 25 years. That orbiting telescope was a generous gift to the next generation from the people who worked on the project for decades before it launched. HST’s deep space images amazed, motivated and inspired many of us on Earth. The GMT project team dreams of passing on a similar gift for future generations.</p><img src="https://counter.theconversation.com/content/49927/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Buddy Martin works for Steward Observatory, part of the University of Arizona. He receives funding from the Giant Magellan Telescope Organization. The University of Arizona is a partner in the Giant Magellan Telescope.</span></em></p><p class="fine-print"><em><span>Dae Wook Kim works for College of Optical Sciences and Richard F. Caris Mirror Lab, part of the University of Arizona. He receives funding from the Giant Magellan Telescope Organization.</span></em></p>The laws of physics dictate that to pick out ever fainter objects from space and see them more sharply, we’re going to need a bigger telescope. And that means we need massive mirrors.Buddy Martin, Project Scientist at the Steward Observatory and Associate Research Professor of Optical Sciences, University of ArizonaDaewook Kim, Associate Professor of Optical Sciences, University of ArizonaLicensed 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.