tag:theconversation.com,2011:/uk/topics/supermoon-6081/articlesSupermoon – The Conversation2021-05-25T09:34:12Ztag:theconversation.com,2011:article/1614712021-05-25T09:34:12Z2021-05-25T09:34:12ZSuper blood Moon: everything you need to know about the lunar eclipse<figure><img src="https://images.theconversation.com/files/402551/original/file-20210525-19-2gg6kp.jpg?ixlib=rb-1.1.0&rect=363%2C0%2C6765%2C4230&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/panoramic-image-total-lunar-eclipse-supermoon-624968915">Shutterstock/CHEN HSI FU</a></span></figcaption></figure><p>Throughout history, lunar eclipses have seemed dramatic. The Moon’s grey-white disc deepens to yellow and orange and finally a dark red cast – this gives a lunar eclipse its nickname of <a href="https://theconversation.com/blood-moon-lunar-eclipse-myths-from-around-the-world-100548">the blood Moon</a>. </p>
<p>Cultures across the world have thought of the lunar eclipse as a sign of changing fortunes or even ill fortune. The ancient Mesopotamians thought the lunar eclipse was an assault on the king and <a href="https://www.metmuseum.org/blogs/now-at-the-met/2017/solar-eclipse-substitute-king">installed proxy kings</a> during the lunar eclipse so no harm came to their rulers. The Hupa and Luiseño tribes of California thought that the Moon must be <a href="https://www.nationalgeographic.com/science/article/140413-total-lunar-eclipse-myths-space-culture-science">injured or sick during the lunar eclipse</a>.</p>
<p>A total lunar eclipse will be visible from parts of Australia, Asia and the western parts of North and South America on May 26. This coincides <a href="https://theconversation.com/supermoon-how-an-illusion-makes-the-full-moon-appear-bigger-than-it-really-is-159721">with a supermoon</a> – a point where the full Moon is closest to Earth.</p>
<h2>What is a lunar eclipse?</h2>
<p>The physical causes of the lunar eclipse are more straightforward than illness, injury or bad luck. A lunar eclipse takes place when the Moon moves into the Earth’s shadow. The Earth has to be directly between the Sun and the Moon, and a lunar eclipse can only take place during a full Moon. </p>
<p>First, the Moon moves into the penumbra – the part of the Earth’s shadow where not all of the light from the Sun is blocked out. Part of the Moon’s disc will look dimmer than a regular full Moon.</p>
<p>Where things get interesting – and strange – is when the Moon moves into the Earth’s umbra, where direct light from the Sun is totally blocked out by the Earth. This means the only light reflecting off the Moon’s disc has already been refracted, or bent, by the Earth’s atmosphere. </p>
<figure class="align-center ">
<img alt="Diagram showing what happens during a lunar and a solar eclipse." src="https://images.theconversation.com/files/402554/original/file-20210525-13-5tn49g.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/402554/original/file-20210525-13-5tn49g.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=603&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402554/original/file-20210525-13-5tn49g.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=603&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402554/original/file-20210525-13-5tn49g.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=603&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402554/original/file-20210525-13-5tn49g.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=758&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402554/original/file-20210525-13-5tn49g.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=758&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402554/original/file-20210525-13-5tn49g.png?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">
<figcaption>
<span class="caption">A lunar and a solar eclipse.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/solar-lunar-eclipses-vector-166954466">Shutterstock/Alhovik</a></span>
</figcaption>
</figure>
<p>Blue light is refracted and scattered more by the atmosphere. While all wavelengths of light travel at the same speed, when they pass through a different material —- such as passing from the vacuum of space to Earth’s denser atmosphere —- the shorter, bluer wavelengths are refracted and scattered more because of their higher frequency. </p>
<p>This refraction and scattering mean that only longer wavelengths of light reach the Moon and are reflected back to Earth. Red light has a longer wavelength than blue light, which gives the lunar eclipse its characteristic reddish colour. On Earth, we see the same effect during sunrises and sunsets, when the sky has a more reddish glow than during the day.</p>
<p>During a total lunar eclipse, the whole of the lunar disc enters the Earth’s umbra, so lucky Moon gazers will be able to see a full, reddish Moon. This won’t last forever, though. After about 14 minutes, the Moon will move out of Earth’s umbra and back into its penumbra. In total, the lunar eclipse will last a few hours.</p>
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<em>
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Read more:
<a href="https://theconversation.com/blood-moon-lunar-eclipse-myths-from-around-the-world-100548">Blood moon: lunar eclipse myths from around the world</a>
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</em>
</p>
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<h2>How to watch the eclipse</h2>
<p>Unfortunately, in many places including the UK, the Moon will be below the horizon. However, some institutions will be streaming live feeds of the lunar eclipse from their locations. For example, the <a href="https://griffithobservatory.org/">Griffith Observatory in Los Angeles</a> will be streaming the whole lunar eclipse for free. </p>
<p>The Moon moves into the Earth’s penumbra at 10:45am BST, and moves into the Earth’s umbra at 12:11 BST. Even though you can’t necessarily go out stargazing in the dark, you can still follow the eclipse from the comfort of your own home – no late nights or early starts required.</p>
<p>Moon gazers will have a while to wait until the next lunar eclipse. On November 19, there will be a partial lunar eclipse that’s just about visible, low in the sky, with barely any of the Moon in the Earth’s penumbra. But many may have better luck next year on May 16 2022, when there will be a total lunar eclipse, visible from the UK in the small hours.</p><img src="https://counter.theconversation.com/content/161471/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Osnat Katz receives funding from the AHRC and the Science Museum for her research. </span></em></p>A total lunar eclipse will be visible from parts of Australia, Asia and the western parts of North and South America on May 26.Osnat Katz, PhD Candidate in Space History, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1612622021-05-21T20:13:41Z2021-05-21T20:13:41ZSupermoon! Red blood lunar eclipse! It’s all happening at once, but what does that mean?<figure><img src="https://images.theconversation.com/files/402165/original/file-20210521-15-mw9fey.jpg?ixlib=rb-1.1.0&rect=71%2C57%2C4685%2C2874&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A red blood moon is caused by sunlight passing through the Earth's atmosphere. </span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Lunar_eclipse_March_2007.jpg#/media/File:Lunar_eclipse_March_2007.jpg">U.S. Navy/Joshua Valcarcel/WikimediaCommons</a></span></figcaption></figure><p>The first lunar eclipse of 2021 is going to happen during the <a href="https://www.timeanddate.com/eclipse/">early hours of May 26</a>. But this is going to be an especially super lunar event, as it will be a supermoon, a lunar eclipse and a red blood moon all at once. So what does this all mean?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/402166/original/file-20210521-19-1lzx779.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A comparison showing a larger moon and a smaller moon with a 12% difference in size." src="https://images.theconversation.com/files/402166/original/file-20210521-19-1lzx779.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/402166/original/file-20210521-19-1lzx779.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=364&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402166/original/file-20210521-19-1lzx779.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=364&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402166/original/file-20210521-19-1lzx779.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=364&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402166/original/file-20210521-19-1lzx779.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=457&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402166/original/file-20210521-19-1lzx779.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=457&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402166/original/file-20210521-19-1lzx779.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=457&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 Moon appears 12% bigger when it is closest to Earth compared with its appearance when it’s farthest away.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Lunar_perigee_apogee.png#/media/File:Lunar_perigee_apogee.png">Tomruen/WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>What’s a super moon?</h2>
<p>A <a href="https://earthsky.org/astronomy-essentials/what-is-a-supermoon">supermoon occurs</a> when a full or new moon coincides with the Moon’s closest approach to the Earth.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/402169/original/file-20210521-19-1upmozl.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="White lines showing the oblong shape of the moon's orbit." src="https://images.theconversation.com/files/402169/original/file-20210521-19-1upmozl.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/402169/original/file-20210521-19-1upmozl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=522&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402169/original/file-20210521-19-1upmozl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=522&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402169/original/file-20210521-19-1upmozl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=522&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402169/original/file-20210521-19-1upmozl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=655&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402169/original/file-20210521-19-1upmozl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=655&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402169/original/file-20210521-19-1upmozl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=655&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 Moon’s orbit is not a perfect circle as it slowly rotates around Earth.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Moon_apsidal_precession.png#/media/File:Moon_apsidal_precession.png">Rfassbind/WikimediaCommons</a></span>
</figcaption>
</figure>
<p>The Moon’s orbit around Earth is not perfectly circular. This means the Moon’s distance from Earth varies as it goes around the planet. The closest point in the orbit, called the perigee, is roughly <a href="https://www.timeanddate.com/astronomy/moon/lunar-perigee-apogee.html">28,000 miles</a> closer to Earth than the farthest point of the orbit. A full moon that <a href="https://theconversation.com/supermoons-are-big-and-bright-but-not-as-rare-as-the-hype-would-suggest-68270">happens near the perigee is called a supermoon</a>.</p>
<p>So why is it super? The relatively close proximity of the Moon makes it seem a little bit bigger and brighter than usual, though the difference between a supermoon and a normal moon is usually hard to notice unless you’re looking at two pictures side by side.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/402173/original/file-20210521-15-1rocqcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the relative position of the Earth and Moon and how this corresponds with the phases of the Moon." src="https://images.theconversation.com/files/402173/original/file-20210521-15-1rocqcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/402173/original/file-20210521-15-1rocqcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=240&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402173/original/file-20210521-15-1rocqcy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=240&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402173/original/file-20210521-15-1rocqcy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=240&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402173/original/file-20210521-15-1rocqcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=302&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402173/original/file-20210521-15-1rocqcy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=302&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402173/original/file-20210521-15-1rocqcy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=302&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 phases of the Moon correspond to how much of the lit–up side you can see from Earth.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Moon_phases_en.jpg#/media/File:Moon_phases_en.jpg">Orion 8/WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>How does a lunar eclipse work?</h2>
<p>A lunar eclipse happens when the Earth’s shadow covers all or part of the Moon. This can only happen during a full moon, so first, it helps to understand what makes a full moon.</p>
<p>Like the Earth, half of the Moon is illuminated by the sun at any one time. A full moon happens when the Moon and the Sun are on opposite sides of the Earth. This allows you see the entire lit-up side, which looks like a round disc in the night sky.</p>
<p>If the Moon had a totally flat orbit, every full moon would be a lunar eclipse. But the Moon’s orbit is tilted by about <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Solar/lunecl.html">5 degrees relative to Earth’s orbit</a>. So, most of the time a full moon ends up a little above or below the shadow cast by the Earth. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/402170/original/file-20210521-13-j8e7a1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing the orbits of the Earth and the moon and Earth's shadow." src="https://images.theconversation.com/files/402170/original/file-20210521-13-j8e7a1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/402170/original/file-20210521-13-j8e7a1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402170/original/file-20210521-13-j8e7a1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402170/original/file-20210521-13-j8e7a1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402170/original/file-20210521-13-j8e7a1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402170/original/file-20210521-13-j8e7a1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402170/original/file-20210521-13-j8e7a1.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 lunar eclipse occurs when the Moon passes through Earth’s shadow.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Geometry_of_a_Lunar_Eclipse.svg#/media/File:Geometry_of_a_Lunar_Eclipse.svg">Sagredo/WikimediaCommons</a></span>
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</figure>
<p>But twice in each lunar orbit, the Moon is on the same horizontal plane as both the Earth and Sun. If this corresponds to a full moon, the Sun, the Earth and the Moon will form a straight line and the Moon will pass through the Earth’s shadow. This results in a <a href="https://svs.gsfc.nasa.gov/4158">total lunar eclipse</a>. </p>
<p>To see a lunar eclipse, you need to be on the night side of the Earth while the <a href="http://www.mreclipse.com/Special/LEprimer.html">Moon passes through the shadow</a>. The best place to see the eclipse on May 26, 2021, will be the middle of the Pacific Ocean, Australia, the East Coast of Asia and the West Coast of the Americas. It will be visible on the eastern half of the U.S., but only the very earliest stages before the Moon sets. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/402176/original/file-20210521-15-199f9vt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A red hued moon with a shadow on the top." src="https://images.theconversation.com/files/402176/original/file-20210521-15-199f9vt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/402176/original/file-20210521-15-199f9vt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=492&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402176/original/file-20210521-15-199f9vt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=492&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402176/original/file-20210521-15-199f9vt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=492&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402176/original/file-20210521-15-199f9vt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=618&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402176/original/file-20210521-15-199f9vt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=618&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402176/original/file-20210521-15-199f9vt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=618&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 Earth’s atmosphere gives the Moon a blood-red glow during total lunar eclipses.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Eclipse_and_Super_blue_blood_moon_31.01.2018_DSCN9664.jpg#/media/File:Eclipse_and_Super_blue_blood_moon_31.01.2018_DSCN9664.jpg">Irvin Calicut/WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Why does the moon look red?</h2>
<p>When the Moon is completely covered by Earth’s shadow it will darken, but doesn’t go completely black. Instead, it takes on a red color, which is why total lunar eclipses are sometimes called red or blood moons. </p>
<p>[<em>Like what you’ve read? Want more?</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=likethis">Sign up for The Conversation’s daily newsletter</a>.]</p>
<p>Sunlight contains all colors of visible light. The particles of gas that make up Earth’s atmosphere are more likely to scatter blue wavelengths of light while redder wavelengths pass through. This is called <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html">Rayleigh scattering</a>, and it’s why the <a href="https://www.physicsclassroom.com/class/light/Lesson-2/Blue-Skies-and-Red-Sunsets">sky is blue and sunrises and sunsets are often red</a>. </p>
<p>In the case of a lunar eclipse, red light can pass through the Earth’s atmosphere and is refracted – or bent – toward the Moon, while blue light is filtered out. This leaves the moon with a <a href="https://www.timeanddate.com/eclipse/why-does-moon-look-red-lunar-eclipse.html">pale reddish hue during an eclipse</a>.</p>
<p>Hopefully you will be able to go see this super lunar eclipse. When you do, now you will know exactly what makes for such a special sight. </p>
<p><em>Portions of this story originally appeared in a <a href="https://theconversation.com/look-up-at-the-super-blue-blood-full-moon-jan-31-heres-what-youll-see-and-why-89738">previous article</a> published on Jan. 24, 2018.</em></p><img src="https://counter.theconversation.com/content/161262/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shannon Schmoll receives funding from the Institute of Museum and Library Services and the National Science Foundation.</span></em></p>In the early morning of May 26, 2021, there will be a super blood-red lunar eclipse. The show will be spectacular and can all be explained by the orbits of the Earth and Moon.Shannon Schmoll, Director, Abrams Planetarium, Department of Physics and Astronomy, Michigan State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1597212021-04-26T10:41:18Z2021-04-26T10:41:18ZSupermoon: how an illusion makes the full Moon appear bigger than it really is<figure><img src="https://images.theconversation.com/files/397026/original/file-20210426-23-dhor35.jpg?ixlib=rb-1.1.0&rect=218%2C102%2C3566%2C2195&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/full-moon-sky-755632231">Shutterstock/Sergey Nivens</a></span></figcaption></figure><p>No matter where you are in the world, and no matter how light the skies are, the Moon is always there. Our <a href="https://theconversation.com/five-moon-myths-and-how-to-disprove-them-yourself-131165">only natural satellite</a> has inspired literature, art and science for thousands of years.</p>
<p>As the days lengthen in the northern hemisphere, it gets harder to spot some of the fainter stars in the sky. But our Moon is still there, and every few months we have a special sighting. </p>
<p>Not only is the Moon on 26 April a full Moon, it’s also what is known as a supermoon – and the first of the year. To understand why it is a supermoon, it’s important to understand a little more about why different parts of the Moon are lit up at different times of the month, and also a little more about the Moon’s orbit.</p>
<h2>Phases of the Moon</h2>
<p>The reason we see different proportions <a href="https://theconversation.com/to-the-moon-and-beyond-1-what-we-learned-from-landing-on-the-moon-and-why-we-stopped-going-119701">of the Moon</a> illuminated at different times of the month, or in different phases, is that the Moon is at different points in its orbit around Earth relative to the Sun. </p>
<p>When the Moon, the Earth and the Sun are all lined up together with the Earth between the Moon and Sun, sunlight shines on the whole lunar surface and is reflected back to Earth. On Earth, this is known as a full Moon. </p>
<p>When the Moon is between Earth and the Sun, no sunlight can reflect off its surface, and this is a new Moon. In between, only part of the Moon’s surface reflects sunlight, giving it different phases, as you can see in the diagram below.</p>
<figure class="align-center ">
<img alt="Diagram showing the moon's phases as it orbits Earth." src="https://images.theconversation.com/files/397029/original/file-20210426-17-oy57hu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397029/original/file-20210426-17-oy57hu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=363&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397029/original/file-20210426-17-oy57hu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=363&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397029/original/file-20210426-17-oy57hu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=363&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397029/original/file-20210426-17-oy57hu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=456&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397029/original/file-20210426-17-oy57hu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=456&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397029/original/file-20210426-17-oy57hu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=456&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Phases of the moon.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/moon-phases-moons-orbit-around-earth-120511270">Shutterstock/Redsapphire</a></span>
</figcaption>
</figure>
<p>What’s more, <a href="https://theconversation.com/how-did-the-moon-end-up-where-it-is-114930">the Moon’s orbit</a> around the Earth isn’t perfectly circular – it’s a very slightly squashed ellipse. This that means sometimes the Moon is closer to the Earth than at other times. The Moon’s closest approach to Earth is called its perigee, and a full Moon at or close to perigee is called a supermoon. </p>
<p>More technically, it’s also known as a perigee syzygy. The opposite phenomenon – when the full Moon is furthest away from Earth in its orbit – is called an apogee syzygy or micromoon. Obviously the supermoon is not a new phenomenon, but its name is quite new – the word doesn’t appear before the 1970s.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/five-moon-myths-and-how-to-disprove-them-yourself-131165">Five Moon myths – and how to disprove them yourself</a>
</strong>
</em>
</p>
<hr>
<p>Since the Moon is so big and bright compared to other objects in the night sky, it’s not hard to see on a clear night. To see the supermoon, the issues are working out when it rises and sets.</p>
<p>In the UK, the Moon rises in the east just before 7.30pm on Monday April 26 and sets in the west just after 6.00am on Tuesday April 27. It’ll be low in the sky, so try to get to a high place like a hill to see the supermoon. </p>
<p>If you don’t mind staying up late or getting up very early, look south around 4.40am. The Moon, Jupiter and Saturn will all be low in the sky and visible to the naked eye – a treat for early birds or night owls.</p>
<h2>The moon illusion</h2>
<p>There’s one catch to all this supermoon business. The Moon doesn’t actually look that much bigger in the sky compared to a normal full Moon. But it sometimes looks bigger when it’s closer to the horizon. Why is this, when its size in the sky doesn’t change very much when it orbits closer to Earth?</p>
<p>This is known as <a href="https://www.uww.edu/Documents/colleges/cls/Departments/Psychology/Mccread_Moon_Illusions.pdf">the Moon illusion</a>, and it really is an illusion. If you cover the Moon with your thumb, you’ll always be able to block it out, whether it looks tiny high up in the sky or whether it looks huge closer to the horizon. </p>
<figure class="align-center ">
<img alt="A full moon above trees." src="https://images.theconversation.com/files/397025/original/file-20210426-23-1ijfrdk.jpg?ixlib=rb-1.1.0&rect=99%2C28%2C4608%2C3308&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/397025/original/file-20210426-23-1ijfrdk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=423&fit=crop&dpr=1 600w, https://images.theconversation.com/files/397025/original/file-20210426-23-1ijfrdk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=423&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/397025/original/file-20210426-23-1ijfrdk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=423&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/397025/original/file-20210426-23-1ijfrdk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=531&fit=crop&dpr=1 754w, https://images.theconversation.com/files/397025/original/file-20210426-23-1ijfrdk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=531&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/397025/original/file-20210426-23-1ijfrdk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=531&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The moon appears bigger when it’s near the horizon.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/supermoon-moon-great-sunset-view-big-501311485">Shutterstock/Paramonov Alexander</a></span>
</figcaption>
</figure>
<p>People have known about this optical illusion <a href="https://doi.org/10.1068%2Fp050377">for thousands of years</a>, but we still don’t completely understand how or why it comes about. </p>
<p>We do know it’s a psychological illusion, and probably at least partly due to the brain thinking that objects <a href="https://brill.com/view/journals/sv/20/1-2/article-p155_8.xml">near the horizon</a> must be closer to us. There are dozens of competing explanations, and most of them are to do with how our brains process information. </p>
<p>So although Monday’s supermoon might not objectively look much bigger in the sky, being low on the horizon could subjectively make it look much bigger to us anyway. Whatever the cause of the Moon illusion or the size of the Moon in the sky, here’s hoping for clear skies.</p><img src="https://counter.theconversation.com/content/159721/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Osnat Katz receives funding from the AHRC and Science Museum as part of her PhD. </span></em></p>April 26 is the first supermoon of the year.Osnat Katz, PhD Candidate in Space History, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1580612021-03-29T03:48:38Z2021-03-29T03:48:38ZWhy is the Moon bright? Is Easter a full moon? How long does a full moon last? Your Moon questions answered by an astronomer<figure><img src="https://images.theconversation.com/files/392135/original/file-20210329-19-14z8pkd.jpg?ixlib=rb-1.1.0&rect=0%2C44%2C3302%2C2282&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>If you stepped outside on the weekend and thought, “Gosh, the full moon looks nice tonight”, you are not alone. </p>
<p>According to Google Trends, Moon-related searches are up by more than 60% over the past week in Australia, led by Western Australia and Queensland. </p>
<p>Technically, the Moon is <a href="https://www.timeanddate.com/moon/phases/australia/sydney">currently</a> “waning gibbous” which means the moment of maximum fullness has passed, and it’s now starting to look smaller. But it’s still quite spectacular.</p>
<p>As someone teaching first-year astronomy at the moment, where much time is spent discussing the Moon, here are my answers to some of the most common recent Moon questions.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/how-big-is-the-moon-let-me-compare-118840">How big is the Moon? Let me compare ...</a>
</strong>
</em>
</p>
<hr>
<h2>1. A full moon is how many times brighter than a half moon?</h2>
<p>You might think a half moon (first quarter or last quarter, depending on where you are in the phases) is half as bright as the full moon. However, if you add up all the light being reflected from the Moon to us here on Earth, a half moon is a fair bit <em>less</em> than half as bright as the full moon. In fact, the full moon is <a href="https://skyandtelescope.org/astronomy-news/how-bright-moon-exactly/#:%7E:text=Yet%20the%20full%20Moon%20is,Earth's%20perspective%2C%20with%20few%20shadows.">roughly six times</a> brighter than the half moon.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/B22I9Z45yrM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>The main reason for this comes down to shadows. When the Moon is full, the Earth is between the Sun and the Moon. So when you look at the Moon rising in the evening, the Sun has just set, behind your back. </p>
<p>That means the side of the Moon facing Earth is fully illuminated. With the Sun at our backs, shadows cast by objects on the Moon are pointing <em>away</em> from us, hidden from view. So we see the maximum amount of the Moon lit up, nice and bright.</p>
<p>At half moon, however, the Sun is shining onto the Moon from one side so the craters, mountains, rocks and pebbles on the Moon all cast shadows. That reduces the amount of the Moon’s surface that’s lit up, so less light is reflected towards us than you’d otherwise expect. </p>
<p>Interestingly, the actual surface of the Moon isn’t that reflective. If the Moon and Venus were side by side and you <a href="https://apod.nasa.gov/apod/ap081204.html">zoomed in</a> to look at the surface brightness of a patch on Venus and compared it with the surface brightness of a patch on the Moon, you’d see the patch on <a href="https://www.reddit.com/r/space/comments/3vt50d/occultation_of_venus_by_the_moon_1272015_los/">Venus is brighter</a>. It’s more reflective because Venus has a lot of clouds that help reflect light back to Earth.</p>
<p>But because the Moon is closer to Earth, it looks bigger than Venus, so the total amount of light that is reflected back to us is bigger. When you look up at night, the Moon will seem much brighter than Venus.</p>
<p>There’s one extra reason the full moon is extra bright - and it’s called the <a href="https://en.wikipedia.org/wiki/Opposition_surge">opposition surge</a>. When the Moon is full (or almost full), the surface we see appears to be a little bit brighter than at all other times. </p>
<p>While the fact that shadows are hidden is part of the puzzle, that isn’t enough to explain all of the brightening of the Moon in the day or so around full moon. The “<a href="https://en.wikipedia.org/wiki/Opposition_surge">opposition surge</a>” is the final piece in the puzzle that makes the full moon so much brighter than the half moon. It’s something we see in all other rocky and icy objects in the Solar system, too.</p>
<h2>2. Why is the Moon bright?</h2>
<p>At the time of writing, we’re within 24 hours of full moon, so it looks big and bright in the sky. It looks so much bigger than everything else in the night sky because it’s near us, and so bright because it’s reflecting light from the Sun. </p>
<p>But the Moon is moving away from Earth at <a href="https://www.bbc.com/news/science-environment-12311119">almost 4cm per year</a>. In the olden days, it would have been even bigger and brighter. It would have been much closer to Earth if we’d been around when Earth was young. However, the Sun was a fair bit less luminous back then, so it’s hard to say exactly how bright the Moon would have been.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/392132/original/file-20210329-17-lx5eda.jpg?ixlib=rb-1.1.0&rect=8%2C8%2C5334%2C2603&q=45&auto=format&w=1000&fit=clip"><img alt="A full moon in the sky over a Queensland beach" src="https://images.theconversation.com/files/392132/original/file-20210329-17-lx5eda.jpg?ixlib=rb-1.1.0&rect=8%2C8%2C5334%2C2603&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/392132/original/file-20210329-17-lx5eda.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/392132/original/file-20210329-17-lx5eda.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/392132/original/file-20210329-17-lx5eda.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/392132/original/file-20210329-17-lx5eda.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=369&fit=crop&dpr=1 754w, https://images.theconversation.com/files/392132/original/file-20210329-17-lx5eda.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=369&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/392132/original/file-20210329-17-lx5eda.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=369&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">In the olden days, the Moon would have been closer to Earth than it is now.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>3. Is Easter a full Moon?</h2>
<p>No. Easter is the first Sunday after the first full moon after the March equinox. </p>
<p>The March equinox is the point in the year when the Sun crosses the Equator in the sky, passing from the southern hemisphere to the northern hemisphere. </p>
<p>To astronomers, this is the start of the northern hemisphere’s spring; for those of us in the southern hemisphere, it marks the start of astronomical autumn. The March equinox typically falls around March 21.</p>
<p>The time between two consecutive full moons is roughly 29.5 days. This means the date of Easter can move around quite a lot.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-all-the-super-buzz-about-the-supermoon-68480">Why all the super buzz about the supermoon?</a>
</strong>
</em>
</p>
<hr>
<h2>4. What is the worm Moon?</h2>
<p>This is a US thing. According to US <a href="https://www.usatoday.com/story/news/nation/2021/03/26/full-worm-moon-rise-sunday-evening-but-supermoon/6999775002/">reports</a>, the name might refer to <a href="https://edition.cnn.com/2021/03/28/world/worm-supermoon-march-2021-scn/index.html">earthworms</a> appearing in the soil as the weather warms in the northern hemisphere. It’s been reported this reflects detail from Native American knowledge systems.</p>
<p>It’s important we recognise traditional astronomy, but it’s worth noting this naming convention comes from Native American culture rather than <a href="http://www.aboriginalastronomy.com.au/">our own Indigenous cultures</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-moon-plays-an-important-role-in-indigenous-culture-and-helped-win-a-battle-over-sea-rights-119081">The Moon plays an important role in Indigenous culture and helped win a battle over sea rights</a>
</strong>
</em>
</p>
<hr>
<h2>5. How long does a full moon last?</h2>
<p>Technically, the exact “moment” the Moon is fullest is the moment it is exactly opposite the Sun in the sky. That happens once every 29 days or so. It is the moment the Moon is most illuminated. </p>
<p>So how long does that last? In reality, it is a split second - the moment of maximum fullness is fleeting.</p>
<p>Either way, if you saw the full moon and thought it might be a nice night to go on a date, you probably have a couple of days left when the Moon will still look impressive and amazing in the sky.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/i-see-the-moon-introducing-our-nearest-neighbour-11499">I see the moon: introducing our nearest neighbour</a>
</strong>
</em>
</p>
<hr>
<img src="https://counter.theconversation.com/content/158061/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner 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>According to Google Trends, Moon-related searches are up by more than 60% over the past week in Australia. We asked an expert in astrophysics to answer your Moon questions.Jonti Horner, Professor (Astrophysics), University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1188402019-07-18T01:05:47Z2019-07-18T01:05:47ZHow big is the Moon? Let me compare …<figure><img src="https://images.theconversation.com/files/284040/original/file-20190715-173325-11n8cww.jpg?ixlib=rb-1.1.0&rect=183%2C115%2C1211%2C824&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The size of the Moon can be deceptive when viewed from Earth.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/ovi90/13196699704/">Flickr/Ovi Gherman</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p>Even though we can see the Moon shining brightly in the night sky – and sometimes in daylight – it’s hard to put into perspective just how large, and just how distant, our nearest neighbour actually is.</p>
<p>So just how big <em>is</em> the <a href="https://solarsystem.nasa.gov/moons/earths-moon/overview/">Moon</a>?</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/DMdhQsHbWTs?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The Moon passing in front of Earth, captured by the Earth Polychromatic Imaging Camera (EPIC), more than a million kilometres away from our planet.</span></figcaption>
</figure>
<p>That answer isn’t quite as straightforward as you might think. Like Earth, the Moon isn’t a perfect sphere. Instead, it’s slightly squashed (what we call an oblate sphereoid). This means the Moon’s diameter from pole to pole is less than the diameter measured at the equator.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-the-moon-is-such-a-cratered-place-118842">Why the Moon is such a cratered place</a>
</strong>
</em>
</p>
<hr>
<p>But the difference is small, just four kilometres. The equatorial diameter of <a href="https://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html">the Moon</a> is about 3,476km, while the polar diameter is 3,472km.</p>
<p>To see how big that is we need to compare it to something of a similar size, such as Australia.</p>
<h2>From coast to coast</h2>
<p>The distance from <a href="https://www.freemaptools.com/how-far-is-it-between-perth_-australia-and-brisbane-qld_-australia.htm">Perth to Brisbane, as the crow flies, is 3,606km</a>. If you put Australia and the Moon side by side, they look to be roughly the same size.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/284051/original/file-20190715-173360-1nn1to4.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/284051/original/file-20190715-173360-1nn1to4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/284051/original/file-20190715-173360-1nn1to4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=542&fit=crop&dpr=1 600w, https://images.theconversation.com/files/284051/original/file-20190715-173360-1nn1to4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=542&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/284051/original/file-20190715-173360-1nn1to4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=542&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/284051/original/file-20190715-173360-1nn1to4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=681&fit=crop&dpr=1 754w, https://images.theconversation.com/files/284051/original/file-20190715-173360-1nn1to4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=681&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/284051/original/file-20190715-173360-1nn1to4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=681&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 Moon vs Australia.</span>
<span class="attribution"><span class="source">NASA/Google Earth</span></span>
</figcaption>
</figure>
<p>But that’s just one way of looking at things. Although the Moon is about as wide as Australia, it is actually much bigger when you think in terms of surface area. It turns out the surface of the Moon is much larger than that of Australia.</p>
<p>The land area of Australia is some <a href="https://www.australia.gov.au/about-australia/our-country/the-australian-continent">7.69 million square kilometers</a>. By contrast, the surface area of the Moon is <a href="https://solarsystem.nasa.gov/moons/earths-moon/by-the-numbers/">37.94 million square kilometres</a>, close to five times the area of Australia. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/284052/original/file-20190715-173370-1n3nttf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/284052/original/file-20190715-173370-1n3nttf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/284052/original/file-20190715-173370-1n3nttf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=360&fit=crop&dpr=1 600w, https://images.theconversation.com/files/284052/original/file-20190715-173370-1n3nttf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=360&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/284052/original/file-20190715-173370-1n3nttf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=360&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/284052/original/file-20190715-173370-1n3nttf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=452&fit=crop&dpr=1 754w, https://images.theconversation.com/files/284052/original/file-20190715-173370-1n3nttf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=452&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/284052/original/file-20190715-173370-1n3nttf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=452&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 Moon rising above Uluru: You’d need five Australias to cover the land mass of the Moon.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/jurek_durczak/11466759956/">Flickr/jurek d Jerzy Durczak</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<h2>How far is the Moon?</h2>
<p>Asking how far away is the Moon is another of those questions whose answer is more complicated than you might expect.</p>
<p>The Moon moves in an elliptical orbit around the Earth, which means its distance from our planet is constantly changing. That distance can vary by up to 50,000km during a single orbit, which is why the size of the Moon in our sky varies slightly from week to week.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/284236/original/file-20190716-173347-id8trq.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/284236/original/file-20190716-173347-id8trq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/284236/original/file-20190716-173347-id8trq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=364&fit=crop&dpr=1 600w, https://images.theconversation.com/files/284236/original/file-20190716-173347-id8trq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=364&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/284236/original/file-20190716-173347-id8trq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=364&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/284236/original/file-20190716-173347-id8trq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=457&fit=crop&dpr=1 754w, https://images.theconversation.com/files/284236/original/file-20190716-173347-id8trq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=457&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/284236/original/file-20190716-173347-id8trq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=457&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Notice the difference in size? The Moon viewed from Earth at perigee (closest approach at 356,700km on October 26 2007) and apogee (farthest approach at 406,300km on April 3 2007).</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Lunar_perigee_apogee.png">Wikimedia/Tomruen</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The Moon’s orbit is also influenced by every other object in the Solar System. Even when all of that is taken into account, the distance answer is still always changing, because the <a href="https://www.bbc.com/news/science-environment-12311119">Moon is gradually receding from the Earth</a> as a result of the tidal interaction between the two. </p>
<p>That last point is something we’ve been able to better study as a result of the Apollo missions. The astronauts who visited the Moon <a href="https://science.nasa.gov/science-news/science-at-nasa/2004/21jul_llr">placed an array of mirror reflectors on its surface</a>. Those reflectors are the continual target of lasers from the Earth. </p>
<p>By timing how long it takes for that laser light to travel to the Moon and back, scientists are able to measure the distance to the Moon with incredible precision, and to track the Moon’s recession from Earth. The result? The Moon is receding at a speed of 38mm per year – or just under 4 metres per century.</p>
<h2>Drive me to the Moon</h2>
<p>Having said all that, the average distance between the Moon and Earth is 384,402km. So let’s put that into context.</p>
<p>If I were to drive from Brisbane to Perth, following the <a href="https://goo.gl/maps/bZ62An1cBz9944zh6">fastest route suggested by Google</a>, I would cover 4,310km on my road trip. That journey, driving across the breadth of our country, would take around 46 hours.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/284231/original/file-20190716-173376-1mwkrmn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/284231/original/file-20190716-173376-1mwkrmn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/284231/original/file-20190716-173376-1mwkrmn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/284231/original/file-20190716-173376-1mwkrmn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/284231/original/file-20190716-173376-1mwkrmn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/284231/original/file-20190716-173376-1mwkrmn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/284231/original/file-20190716-173376-1mwkrmn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/284231/original/file-20190716-173376-1mwkrmn.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">The full Moon rising over the Perth Hills, in Western Australia, in 2016.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/135630555@N04/22823086188/">Paean Ng/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>If I wanted to clock up enough kilometres to say that I’d covered the distance between the Earth and the Moon, I’d have to make that trip more than 89 times. It would take five-and-a-half months of driving, non-stop, assuming I didn’t run into any traffic jams on the way.</p>
<p>Fortunately, the Apollo 11 astronauts weren’t restricted to Australian speed limits. The command module Columbia took just three days and four hours to reach lunar orbit following its launch on July 16 1969.</p>
<h2>An eclipse coincidence</h2>
<p>The equatorial diameter of the <a href="https://solarsystem.nasa.gov/solar-system/sun/by-the-numbers/">Sun</a> is almost 1.4 million kilometres, which is almost exactly 400 times the diameter of the Moon. </p>
<p>That ratio leads to one of astronomy’s most spectacular quirks – because the distance between the Earth and the Sun (149.6 million kilometres) is almost (but not quite) 400 times the distance between the Earth and the Moon.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-is-a-solar-eclipse-33019">Explainer: what is a solar eclipse?</a>
</strong>
</em>
</p>
<hr>
<p>The result? The Moon and the Sun appear almost exactly the same size in Earth’s sky. As a result, when the Moon and the Sun line up perfectly, as seen from Earth, something wonderful happens – a total eclipse of the Sun.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/2lHb5ruGUyw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The total solar eclipse seen from north Queensland in November 2012.</span></figcaption>
</figure>
<p>Sadly, such spectacular eclipses will eventually come to an end on Earth. Thanks to the Moon’s recession, it will one day be too distant to perfectly obscure the Sun. But that day will be a long time coming, with most estimates suggesting it will occur in something like 600 million years’ time.</p>
<h2>The moonwalkers</h2>
<p>While we’ve dispatched out robot envoys to the icy depths of the Solar System, the Moon remains the only other world on which humanity has walked.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/284252/original/file-20190716-173325-1pnn0bu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/284252/original/file-20190716-173325-1pnn0bu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/284252/original/file-20190716-173325-1pnn0bu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=619&fit=crop&dpr=1 600w, https://images.theconversation.com/files/284252/original/file-20190716-173325-1pnn0bu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=619&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/284252/original/file-20190716-173325-1pnn0bu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=619&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/284252/original/file-20190716-173325-1pnn0bu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=778&fit=crop&dpr=1 754w, https://images.theconversation.com/files/284252/original/file-20190716-173325-1pnn0bu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=778&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/284252/original/file-20190716-173325-1pnn0bu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=778&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Astronaut Buzz Aldrin was the second man to walk on the Moon and one of the few moonwalkers still alive today.</span>
<span class="attribution"><a class="source" href="https://solarsystem.nasa.gov/resources/840/apollo-11-buzz-aldrin/">NASA</a></span>
</figcaption>
</figure>
<p>Fifty years after that first adventure, the number of people to have walked on the Moon who are still alive is in sharp decline. <a href="https://solarsystem.nasa.gov/news/890/who-has-walked-on-the-moon/">Twelve people</a> have had that experience but, as of today, just four remain.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/five-ethical-questions-for-how-we-choose-to-use-the-moon-116801">Five ethical questions for how we choose to use the Moon</a>
</strong>
</em>
</p>
<hr>
<p>Vast as the Moon is, those 12 moonwalkers barely scratched the surface. Hopefully, in the coming years, we will return, to inspire a whole new generation and to continue humanity’s in-person exploration of our nearest celestial neighbour.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/284248/original/file-20190716-173351-17qv15a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/284248/original/file-20190716-173351-17qv15a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/284248/original/file-20190716-173351-17qv15a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=255&fit=crop&dpr=1 600w, https://images.theconversation.com/files/284248/original/file-20190716-173351-17qv15a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=255&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/284248/original/file-20190716-173351-17qv15a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=255&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/284248/original/file-20190716-173351-17qv15a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=320&fit=crop&dpr=1 754w, https://images.theconversation.com/files/284248/original/file-20190716-173351-17qv15a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=320&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/284248/original/file-20190716-173351-17qv15a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=320&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 Moon over the Sydney Opera House.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/paulcarmona/15332847519/">Flickr/Paul Carmon</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure><img src="https://counter.theconversation.com/content/118840/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonti Horner 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>Just 12 people have walked on the Moon and they’ll know better than anyone just how big (or small) the place is. But we can make some comparisons with things on Earth to get a measure of the Moon.Jonti Horner, Professor (Astrophysics), University of Southern QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1053712018-12-11T23:30:28Z2018-12-11T23:30:28ZCurious Kids: How does the Moon, being so far away, affect the tides on Earth?<figure><img src="https://images.theconversation.com/files/244951/original/file-20181111-116841-10bxw8f.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4224%2C3168&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">When the sea level rises to its highest point, we call that high tide. When it falls to its lowest point, that's called low tide.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/bpinzini/4811517787/in/photolist-8kbhBe-t6Wqu-V9E4Rj-bwPoqJ-oY6DQ2-poSVN-8HEPDt-8zzY37-dgfS7Y-5ZWhDN-ooeRhw-oFjni7-drDheu-pgUnWK-7Efezw-WjLGdD-hGrGu4-2cMqEer-cLPprS-275aF2W-4LApJD-o9n4S1-P5NfW-Y9UcXm-oBbG-5a5jJr-VJTPAi-4RMFK7-8zwUKg-nFiY7-o9Fk99-39kKrk-dDYxAm-9pjmWu-qeQwN6-6p9dyV-dNkyY6-23gFUAK-kEBNt4-dNbvbU-NgC4KX-rg8Pyu-4T846v-5jZTGg-fEBa7u-nXAhnv-4r9o1w-7PHt5p-hfyc7-8zwNNn">Flickr/bpinzini</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p><em>This is an article from <a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a>, a series for children. You can send your question to curiouskids@theconversation.edu.au. You might also like the podcast <a href="http://www.abc.net.au/kidslisten/imagine-this/">Imagine This</a>, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.</em> </p>
<hr>
<blockquote>
<p><strong>How does the Moon, being so far away, affect the tides on Earth? – Lachie, age 8, Doreen, Melbourne.</strong></p>
</blockquote>
<hr>
<p>Great question Lachie!</p>
<p>The short answer is that the Moon’s gravity pulls the oceans (and us) towards it. Even though the Moon is so far away, it is large enough that its force of gravity is strong enough to do that.</p>
<p>But before we get into how the Moon affects tides, let’s look at what tides are.</p>
<p>Tides are the rise and fall of water level in the oceans (and lakes, and even in your cup of water, but they’re very small). </p>
<p>When the sea level rises to its highest point, we call that high tide. When it falls to its lowest point, that’s called low tide.</p>
<p>The rise and fall of the tides is known as the tide cycle. If there’s one high tide and one low tide a day, like you would see if you went on holiday to Perth, it’s called a diurnal tide cycle. If there are two high tides and two low tides, like you see in Victoria, it’s called a semi-diurnal tide cycle. </p>
<p>The Moon has the most effect on the tides, but it’s not the only factor that affects them. The Sun and the Earth can also affect the tides. We’ll start with the Moon. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-are-there-living-things-on-different-galaxies-98562">Curious Kids: Are there living things on different galaxies?</a>
</strong>
</em>
</p>
<hr>
<h2>Tides and the Moon</h2>
<p>The Moon affects the tides because of gravity. You will have noticed that every time you jump, you always land back on the ground. This is because the Earth’s gravity is pulling you back down. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/244956/original/file-20181111-116841-1euc09g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&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 Earth’s spinning means that another high tide occurs on the opposite side of the Earth to the Moon.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>The Moon has gravity of its own, which pulls the oceans (and us) towards it. The Moon’s gravitational pull on us is much weaker than Earth’s, so we don’t really notice it, but we can see the Moon’s effect on the liquid water of the oceans. The oceans are pulled towards the Moon’s gravity slightly, causing a bulge or high tide on the side of the Earth closest to the Moon. </p>
<h2>The Earth’s effect</h2>
<p>If the Moon causes a high tide on one side of the Earth, what causes the high tide on the other side?</p>
<p>The Earth is spinning, which is why we have night and day. The Earth’s spinning means that another high tide occurs on the opposite side of the Earth to the Moon. </p>
<p>These two high tides draw water away from the rest of the oceans, causing two low tides between the high tides. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/4UZxzyOVJ8Q?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Why do we have tides? - Forces of Nature with Brian Cox: Episode 2 - BBC One.</span></figcaption>
</figure>
<h2>The Sun</h2>
<p>The Sun, just like the Moon and the Earth, also has its own gravity which can affect the tides. Although the Sun is much larger than the Moon and has more gravity, it’s also much further away, meaning its pull on the tides is less than half as strong as the Moon’s. </p>
<p>It still does have an effect, though. When the Sun and Moon are in line with the Earth (when a full moon or new moon occur), their combined gravity cause very high tides (and very low tides), known as “spring tides.”</p>
<p>When the Sun and Moon are at right angles to each other (during a waxing or waning moon), the Sun helps to cancel out the pull of gravity from the Moon, causing lower high tides and higher than average low tides, known as “neap tides”. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/244955/original/file-20181111-37973-1i6ogp8.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">Lunar and Solar tides diagram.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>So the Moon affects the tides because of gravity, but gravity from the Sun and the spinning of the Earth also change how the tides behave.</p>
<p>Best wishes,</p>
<p>Mark Hemer.</p>
<hr>
<p>
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Read more:
<a href="https://theconversation.com/curious-kids-is-there-anything-hotter-than-the-sun-105748">Curious Kids: Is there anything hotter than the Sun?</a>
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<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/165749/original/image-20170419-32713-1kyojyz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em>Please tell us your name, age and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/105371/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Hemer receives funding from the National Environmental Science Program Earth Systems and Climate Change Hub, and the Australian Renewable Energy Agency.</span></em></p>The Moon has gravity of its own, which pulls the oceans (and us) towards it.Mark Hemer, Senior Research Scientist, Oceans and Atmosphere, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/907792018-01-29T15:24:28Z2018-01-29T15:24:28Z‘Super blue blood moon’ to grace the sky – here’s what we could learn from it<figure><img src="https://images.theconversation.com/files/203557/original/file-20180126-100915-1xkouv8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Blood moon on April 15, 2014.</span> <span class="attribution"><span class="source">Robert Jay GaBany/wikipedia,</span></span></figcaption></figure><p>Something unusual will happen on January 31. A total lunar eclipse, which will be visible from Asia, Australasia and North and Central America, will coincide with a “blue moon” and a “supermoon” in what some are calling a “super blue blood moon”. The event, which for western hemisphere observers happens for the first time in 150 years, will also be the last in a trilogy of supermoons over the past two months. It sounds cool, but how excited should you really be? And is there anything scientists can actually get out of it?</p>
<p>To be honest, I feel pretty conflicted about all the excitement surrounding the supermoon, a term which describes the moon when it is at a close point to the Earth. It’s great that people get excited about astronomy, but the trouble is that a supermoon in itself <a href="https://theconversation.com/big-moon-rising-go-and-have-a-look-but-dont-be-fooled-into-thinking-its-all-that-super-29227">is not really all that special</a>. </p>
<p>Since the moon follows an elliptical orbit around the Earth, the distance between the two bodies changes, ranging from about 360,000km to 406,000km. At its closest point, perigee, the moon will obviously appear largest. Such a “maximoon” has an apparent diameter about 13% larger than a “minimoon” at its most distant point, apogee. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/203561/original/file-20180126-100926-1t3dezv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/203561/original/file-20180126-100926-1t3dezv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=408&fit=crop&dpr=1 600w, https://images.theconversation.com/files/203561/original/file-20180126-100926-1t3dezv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=408&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/203561/original/file-20180126-100926-1t3dezv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=408&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/203561/original/file-20180126-100926-1t3dezv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=513&fit=crop&dpr=1 754w, https://images.theconversation.com/files/203561/original/file-20180126-100926-1t3dezv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=513&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/203561/original/file-20180126-100926-1t3dezv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=513&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Super Moon in 2016.</span>
<span class="attribution"><span class="source">Betty Wills (Atsme)/wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The effect of a maximoon is <a href="http://www.telegraph.co.uk/news/0/supermoon-give-stargazers-spectacular-night-sky-show/">often exaggerated</a> – it is only about 7% larger and 15% brighter than the average moon. This is hardly noticeable when looking at it with the unaided eye. In fact, if you’ve seen the moon looking huge at some point, it was probably due to an <a href="http://www.skyandtelescope.com/observing/moon-illusion-confusion11252015/">optical illusion</a> rather than it being near perigee. It’s not fully understood why, but the moon seen close to the horizon just appears larger than when it’s high in the sky.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/tARtQkWdZSM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>The mechanisms behind the maximoon have long been known, with astronomers referring to it as “perigee full moon” or a “perigee syzygy”, a lovely word that means three celestial bodies in a line. Unsurprisingly, the term supermoon has proved more popular. <a href="https://www.britannica.com/biography/Richard-Nolle">Coined by an astrologer in 1979</a>, it wasn’t really used at all widely until March 2011 when the Japanese earthquake and tsunami was <a href="http://www.dailymail.co.uk/sciencetech/article-1365225/Japan-earthquake-tsunami-Did-supermoon-cause-todays-natural-disaster.html">erroneously linked to a supermoon</a> which actually happened eight days later. </p>
<p>What’s more, a supermoon isn’t exactly the same thing as a maximoon. If you waited until the instant of full moon exactly coincided with the instant of perigee, supermoons would be vanishingly rare. But an unscientific fudge factor is usually included, allowing the full moon to be “near” perigee – <a href="https://www.jpl.nasa.gov/edu/news/2017/11/15/whats-a-supermoon-and-just-how-super-is-it/">typically 90% or closer</a>. Change the size of the fudge factor and you can have as many or as few supermoons as you like. In fact, for this week’s event, the moon is closest to Earth at about 10:00 UTC on January 30 but the full moon is not till over a day later when it is about 1,200km farther away.</p>
<h2>Blue vs blood moon</h2>
<p>A blue moon does not appear blue. It’s just a term that, in the 1940s, was <a href="http://www.jodrellbank.net/blue-moon/">mistakenly used</a> to describe a rare occasion: the second full moon in a calendar month. Full moons are separated by about 29.5 days and so typically occur in different months, with a blue moon appearing on average every 30 months or so. </p>
<p>A blood moon on the other hand actually appears dusky red. The name, which is not used by scientists, apparently derives from <a href="https://en.wikipedia.org/wiki/Blood_moon_prophecy">apocalyptic Biblical prophecy</a>. As with supermoon, the term only became popular very recently, in this case in 2014 when a series of four over 18 months <a href="https://www.washingtonpost.com/national/religion/blood-moon-sets-off-apocalyptic-debate-among-some-christians/2014/04/15/00b76502-c4be-11e3-9ee7-02c1e10a03f0_story.html">spawned a best-selling book</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/203558/original/file-20180126-100926-1grwtwa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/203558/original/file-20180126-100926-1grwtwa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=482&fit=crop&dpr=1 600w, https://images.theconversation.com/files/203558/original/file-20180126-100926-1grwtwa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=482&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/203558/original/file-20180126-100926-1grwtwa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=482&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/203558/original/file-20180126-100926-1grwtwa.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=605&fit=crop&dpr=1 754w, https://images.theconversation.com/files/203558/original/file-20180126-100926-1grwtwa.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=605&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/203558/original/file-20180126-100926-1grwtwa.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=605&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Image depicting the various phases of a lunar eclipse or</span>
<span class="attribution"><span class="source">Patrick Murtha/wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The effect is caused by a lunar eclipse, when the moon is on the far side of the sun from the Earth – aligned so that it passes into the Earth’s shadow. The moon darkens very considerably and is only lit by the traces of sunlight refracted through the Earth’s atmosphere. The blue component of the sunlight is scattered to large angles by small particles in the atmosphere leaving only the longer wavelength red light to illuminate the moon. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=299&fit=crop&dpr=1 600w, https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=299&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=299&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=376&fit=crop&dpr=1 754w, https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=376&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=376&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 lunar eclipse happens when the moon is completely in the Earth’s shadow.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Solar_lunar_eclipse_diagram.png">Tomruen</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Over this century, there will be <a href="https://eclipse.gsfc.nasa.gov/LEcat5/LE2001-2100.html">85 total lunar eclipses</a>. This particular one <a href="https://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2018Jan31T.pdf">will be visible</a> from Asia, Australasia, North and Central America, but not from Western Europe or much of Africa and South America (though anyone can still enjoy the near full moon). </p>
<h2>Research potential</h2>
<p>A lunar eclipse is a great opportunity for public viewing, but there are still things that scientists can learn from the event. The details of how the sunlight we see reflected from the moon during eclipse has been altered, scattered and absorbed on its way through our atmosphere, and how this is affected by, for example, volcanic eruptions or even meteor showers, are <a href="http://bit.ly/2DL0QcC">still being studied</a>. </p>
<p>But in recent years, there has been a resurgence of interest in studying lunar eclipses from a surprising source, the discovery of planets orbiting other stars. If we see an “exoplanet” pass across the face of its parent star, a small fraction of the starlight we collect will have passed through the planet’s atmosphere. Looking at spectra – measurements of light broken down by wavelength – taken during such a transit with those taken out of transit can help determine the composition of the atmosphere. This could include biosignatures such as oxygen, ozone or methane – which might give away the presence of extraterrestrial life. </p>
<p>A lunar eclipse is a perfect opportunity to study the details of the same effect close to home – sunlight reflected from the moon during eclipse has passed through the Earth’s atmosphere and been imprinted with its characteristics. This means the Earth <a href="http://bit.ly/2nnMQze">takes the place</a> of a transiting exoplanet. Various lunar eclipse studies <a href="http://bit.ly/2noSReo">are being conducted</a> ahead of observations with upcoming facilities – such as the <a href="https://www.jwst.nasa.gov/">James Webb Space Telescope</a> and the <a href="https://www.eso.org/public/unitedkingdom/teles-instr/elt/">European Extremely Large Telescope</a> – which have the potential to study the atmospheres of distant Earth-like planets.</p>
<p>But even if you’re not a scientist, do go out and have a look this week. You are likely to see a slightly bigger moon than usual, exaggerated in size by the <a href="https://en.wikipedia.org/wiki/Moon_illusion">moon illusion</a> as it rises or sets, and in some parts of the globe appearing dark and red from the lunar eclipse. Perhaps the event could inspire you to take up moon gazing. There’s so much to love – such as the shadows of mountains and crater walls at their most dramatic and the incredible feeling of flying across the lunar landscape when you view it through a telescope. As far as I’m concerned, every moon is super.</p><img src="https://counter.theconversation.com/content/90779/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tim O'Brien has received funding from the UK Science & Technology Facilities Council. From 2016-2018 he has been President of the Society for Popular Astronomy.</span></em></p>Studying lunar eclipse could help us work out what’s happening on exoplanets.Tim O'Brien, Professor of Astrophysics and Associate Director of Jodrell Bank Centre for Astrophysics, University of ManchesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/897382018-01-24T11:40:34Z2018-01-24T11:40:34ZLook up at the super blue blood full moon Jan. 31 – here’s what you’ll see and why<figure><img src="https://images.theconversation.com/files/203104/original/file-20180123-33560-1wukgov.jpg?ixlib=rb-1.1.0&rect=137%2C0%2C1269%2C864&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">As long as clouds don't get in the way, the view should be spectacular.</span> <span class="attribution"><a class="source" href="https://images.nasa.gov/details-GSFC_20171208_Archive_e001982.html">NASA Goddard</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><a href="https://www.timeanddate.com/astronomy/moon/blue-moon.html">During the early hours of Jan. 31</a>, there will be a full moon, a total lunar eclipse, a blue moon and a supermoon – all at the same time. None of these things is really all that unusual by itself. What is rare is that they’re happening all together on one day.</p>
<h2>What makes the moon look full?</h2>
<p>Like the Earth, half the moon is illuminated by the sun at any one time. The <a href="https://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::800::600::/sites/dl/free/0072482621/78778/Lunar_Nav.swf::Lunar%20Phases%20Interactive">moon orbits around the Earth</a> and as a result we see different amounts of the lit-up side.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/203083/original/file-20180123-33535-18ufglr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/203083/original/file-20180123-33535-18ufglr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/203083/original/file-20180123-33535-18ufglr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=240&fit=crop&dpr=1 600w, https://images.theconversation.com/files/203083/original/file-20180123-33535-18ufglr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=240&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/203083/original/file-20180123-33535-18ufglr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=240&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/203083/original/file-20180123-33535-18ufglr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=302&fit=crop&dpr=1 754w, https://images.theconversation.com/files/203083/original/file-20180123-33535-18ufglr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=302&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/203083/original/file-20180123-33535-18ufglr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=302&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 phases of the moon visible from Earth are related to its revolution around our planet.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Moon_phases_en.jpg">Orion 8</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>A full moon is when we see its entire lit-up side. This occurs every 29.5 days, when the moon is directly opposite the sun relative to the Earth. Jan. 31 will be our <a href="http://www.moonconnection.com/moon-january-2018.phtml">next full moon in the lunar cycle</a>. </p>
<h2>What’s a lunar eclipse?</h2>
<p>The moon’s orbit is tilted by about 5 degrees relative to the Earth’s orbit. So, most of the time the moon ends up a little above or below the path Earth follows as it revolves around the sun. But twice in each lunar cycle, the moon does <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Solar/lunecl.html">cross into our planet’s orbital plane</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=299&fit=crop&dpr=1 600w, https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=299&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=299&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=376&fit=crop&dpr=1 754w, https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=376&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/203111/original/file-20180123-33571-lpjctf.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=376&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 lunar eclipse happens when the moon is completely in the Earth’s shadow.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Solar_lunar_eclipse_diagram.png">Tomruen</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>If that crossing corresponds to a full moon, the moon will pass into the Earth’s shadow, resulting in <a href="http://www.mreclipse.com/Special/LEprimer.html">a total lunar eclipse</a>. Since the moon needs to be behind the Earth, relative to the sun, a lunar eclipse can only happen on a full moon.</p>
<p>To see the phenomenon, you need to be on the night side of the Earth; <a href="https://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2018Jan31T.pdf">this eclipse will be visible mostly</a> in Asia, Australia, the Pacific and North America. But don’t worry if you miss it, lunar eclipses happen on average a couple times a year. The next one visible in North America <a href="https://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2019Jan21T.pdf">will be on Jan. 21, 2019</a>.</p>
<h2>A blue moon that looks red</h2>
<p>When a lunar eclipse happens, the moon appears to darken as it moves into the Earth’s shadow called the umbra. When the moon is all the way in shadow it doesn’t go completely dark; instead, it looks red due to a <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html">process called Rayleigh scattering</a>. The gas molecules of Earth’s atmosphere scatter bluer wavelengths of light from the sun, while redder wavelengths pass straight through.</p>
<p>This is why we have <a href="http://www.physicsclassroom.com/class/light/Lesson-2/Blue-Skies-and-Red-Sunsets">blue skies and red sunrises and sunsets</a>. When the sun is high in the sky, red light passes straight through to the ground while blue light is scattered in every direction, making it more likely to hit your eye when you look around. <a href="https://www.atoptics.co.uk/atoptics/sunsets.htm">During a sunset</a>, the angle of the sun is lower in the sky and that red light instead passes directly into your eyes while the blue light is scattered away from your line of sight. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/203107/original/file-20180123-33560-r0cofb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/203107/original/file-20180123-33560-r0cofb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/203107/original/file-20180123-33560-r0cofb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=654&fit=crop&dpr=1 600w, https://images.theconversation.com/files/203107/original/file-20180123-33560-r0cofb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=654&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/203107/original/file-20180123-33560-r0cofb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=654&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/203107/original/file-20180123-33560-r0cofb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=822&fit=crop&dpr=1 754w, https://images.theconversation.com/files/203107/original/file-20180123-33560-r0cofb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=822&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/203107/original/file-20180123-33560-r0cofb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=822&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 super blood moon tinted red by scattered light.</span>
<span class="attribution"><a class="source" href="https://images.nasa.gov/details-GSFC_20171208_Archive_e000601.html">GSFC</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>In the case of a lunar eclipse, the sunlight that makes it around Earth passes through our atmosphere and is refracted toward the moon. Blue light is filtered out, leaving the moon <a href="https://www.timeanddate.com/eclipse/why-does-moon-look-red-lunar-eclipse.html">looking reddish during an eclipse</a>.</p>
<p>On top of it all, the Jan. 31 full moon is also a considered a blue moon. There are two different definitions of blue moon. The first is any time a second full moon occurs in a single month. Since there are 29.5 days between two full moons, we usually only end up with one per month. With most months longer than 29.5 days, it occasionally works out that we have two full moons. We already had one on the first of this month and our second will be Jan. 31, making it a blue moon. With this definition our next blue moon is in March, leaving February with no full moon this year.</p>
<p>The second definition of a blue moon states it’s the <a href="https://www.timeanddate.com/astronomy/moon/blue-moon.html">third moon in a season</a> in which there are four moons, which <a href="https://www.space.com/16776-blue-moon-explained-infographic.html">happens about every 2.7 years</a>. We’ll only have three this winter, so the Jan. 31 full moon won’t be blue by this definition. Stargazers will need to wait until May 18, 2019, for a blue moon that fits this older, original definition.</p>
<h2>A supersized supermoon</h2>
<p>Finally, to add the cherry on top, this will also <a href="https://theconversation.com/supermoons-are-big-and-bright-but-not-as-rare-as-the-hype-would-suggest-68270">be a supermoon</a>. The moon’s orbit is not perfectly circular, meaning its distance from Earth varies as it goes through one cycle. The closest point in its orbit is called the perigee. A full moon that happens near perigee is <a href="https://www.space.com/38940-supermoon-facts.html">called a supermoon</a> by some. </p>
<p>This happened with our full moon earlier this month on Jan. 1 and will again on Jan. 31.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/203086/original/file-20180123-33557-n72zr9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/203086/original/file-20180123-33557-n72zr9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/203086/original/file-20180123-33557-n72zr9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=599&fit=crop&dpr=1 600w, https://images.theconversation.com/files/203086/original/file-20180123-33557-n72zr9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=599&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/203086/original/file-20180123-33557-n72zr9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=599&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/203086/original/file-20180123-33557-n72zr9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=752&fit=crop&dpr=1 754w, https://images.theconversation.com/files/203086/original/file-20180123-33557-n72zr9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=752&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/203086/original/file-20180123-33557-n72zr9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=752&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Appearance of an ‘average’ moon versus a supermoon.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Supermoon_comparison.jpg">Marcoaliaslama</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Its proximity makes it seem a little bit bigger and brighter than usual, but that’s the extent of its effects on Earth. The distinction is usually hard to notice unless you’re looking at two pictures side by side.</p>
<p>There are long traditions of giving <a href="https://www.timeanddate.com/astronomy/moon/full-moon-names.html">different moons names</a>. This being a bigger, brighter, reddish-looking blue moon, perhaps we should call the next full moon the super purple moon. The moon will not actually appear purple, nor will have it a cape – but <a href="https://www.nasa.gov/sites/default/files/thumbnails/image/lunar_eclipse_01182018a.png">Jan. 31 is a great time</a> to gaze up and enjoy the night sky.</p><img src="https://counter.theconversation.com/content/89738/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shannon Schmoll does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A bunch of uncommon things all happening at the same time mean this full moon will have some special attributes.Shannon Schmoll, Director, Abrams Planetarium, Department of Physics and Astronomy, Michigan State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/686372016-11-11T13:38:03Z2016-11-11T13:38:03ZGet ready for the biggest ‘supermoon’ in more than six decades<figure><img src="https://images.theconversation.com/files/145486/original/image-20161110-25097-1lqfxeu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This image is an approximation of what the upcoming supermoon will look like.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/sites/default/files/thumbnails/image/full-moon-2016-lro_0.jpg ">Credit: NASA Goddard's Scientific Visualization Studio</a></span></figcaption></figure><p>The biggest “<a href="https://science.nasa.gov/news-articles/2016-ends-with-three-supermoons">supermoon</a>” since 1948 will grace the sky on November 14. But what makes it so super? Well, not much more than the fact that it’ll be a bit bigger than normal, but that’s absolutely no reason not to go outside and look at it anyway. If you miss it, you’ll have to wait to around November 25, 2034 for another chance.</p>
<p>The occurrence of a supermoon, or to give it its proper name, a “super perigee full moon”, <a href="https://theconversation.com/big-moon-rising-go-and-have-a-look-but-dont-be-fooled-into-thinking-its-all-that-super-29227">is not particularly uncommon.</a> It is the result of two regular astronomical events happening at about the same time.</p>
<p>As the moon orbits the Earth it moves around the sky relative to the sun. This means we see different proportions illuminated from one night to the next – an effect known as the phases of the moon. Once per orbit the moon is opposite the sun in the sky, meaning that the side facing the Earth is fully illuminated. This happens about once a month, so hopefully isn’t that unfamiliar to most people.</p>
<p>The other regular event requires little explaining: it is simply <a href="http://www.space.com/30376-supermoon-full-moon-2015-explained.html">the moon’s “perigee”</a>, or closest approach to the Earth. Although the moon orbits the Earth once every 27 days or so (actually about 27 days and eight hours), it doesn’t go round in a perfect circle. Instead it traces out an ellipse or oval shape, getting slightly closer and further from the Earth over the course of its orbit. At its closest the moon is just under 360,000km away, while at its furthest it is at a distance of around 405,000km. The closer an object like the moon is to Earth the larger it appears in the sky.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/145487/original/image-20161110-25070-1t2tcps.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/145487/original/image-20161110-25070-1t2tcps.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/145487/original/image-20161110-25070-1t2tcps.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/145487/original/image-20161110-25070-1t2tcps.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/145487/original/image-20161110-25070-1t2tcps.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/145487/original/image-20161110-25070-1t2tcps.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/145487/original/image-20161110-25070-1t2tcps.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/145487/original/image-20161110-25070-1t2tcps.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">The Moon’s orbit, showing perigee and full moon.</span>
<span class="attribution"><span class="source">Chris North/Cardiff Uni.</span></span>
</figcaption>
</figure>
<p>At around 1:30pm (GMT) on November 14, the Earth, sun and moon will be almost perfectly in a line (an effect known as a “syzygy”), with the moon directly opposite the sun. A couple of hours earlier, at about 11:30am, it will also have reached its closest point to Earth – perigee – at a distance of 356,500km. It will then begin moving further away very slowly – but by the time the sun sets and the moon rises in the UK, it will only be about 50km further away, which isn’t much in the grand scheme of things.</p>
<p>Both of these effects happen about once a month, so you might think that there’s no reason why every full moon shouldn’t be the same. However, there’s another effect that means they get out of sync – the fact that the Earth is orbiting the sun. This means that the moon’s closest approach can occur at any point in its orbit around the Earth.</p>
<p>To see why, fast forward to when the moon will once again be back at the same point in its orbit – in about 27 days. But over those 27 days the Earth has moved round the sun a bit, so the moon has to “catch up” over the course of a couple of days to get back to being opposite the sun, by which point it’s not at perigee anymore. This “catching up” is why the moon orbits the Earth in 27.3 days, but there are between 29 and 30 days between full moons. Over time, the perigee and full moon get more and more out of sync, but after a year or two they get more or less back in sync again.</p>
<h2>Catching the event</h2>
<p>The reason this perigee full moon is quite so “super” is because perigee and full moon happen at almost exactly the same time, so the moon is at its closest possible when it’s also at its fullest. There are a number of other subtle effects that <a href="http://www.ifa.hawaii.edu/%7Ebarnes/ASTR110L_S03/lunarorbit.html">cause the moon’s orbit to vary slightly</a> in size and shape, but this one pips the last few decades’ worth of super perigee full moons by a few hundred kilometres. In 2034, when we’ll have a similarly big supermoon, it will occur within a few minutes of its closest approach, and even then it will be just 100km closer than this month’s full moon.</p>
<p>These differences are pretty small, and with the moon rising so high in the sky, as it does in the winter months, it’ll be quite hard to notice any difference without comparing photographs. But regardless of how big and bright it looks, the moon really is a beautiful object to look at. Of course, it might be cloudy on Monday night – though it can be rather atmospheric to see the bright, full moon through thin cloud. Even if it’s completely overcast, there are plenty of other chances to see the moon as it gradually moves past its full phase over the next few nights so don’t be disheartened. It rises at different times of day and night as it orbits the Earth, so isn’t always up at the same time, but it’s not going anywhere!</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/145556/original/image-20161111-15712-1wq4853.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/145556/original/image-20161111-15712-1wq4853.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/145556/original/image-20161111-15712-1wq4853.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/145556/original/image-20161111-15712-1wq4853.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/145556/original/image-20161111-15712-1wq4853.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/145556/original/image-20161111-15712-1wq4853.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/145556/original/image-20161111-15712-1wq4853.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">
<figcaption>
<span class="caption">The crescent moon is stunning, too.</span>
<span class="attribution"><a class="source" href="https://pixabay.com/en/moon-crescent-moon-moonlight-1653256/">Pixabay</a></span>
</figcaption>
</figure>
<p>The lunar phases will continue unabated, and a few weeks after the full moon the crescent moon will be in the evening skies again (and will also be visible in the daytime) so go and have a look again, and see how it compares. When it’s not full, the terminator (the line between the light and dark parts of the moon) can look amazing through binoculars, as the angle of the sun’s light picks out the shadows of the craters and mountains and gives it a jagged, three-dimensional look.</p>
<p>So if you’ve never really looked at the moon – I mean <em>really</em> looked at it – make this your excuse to go outside and look up.</p><img src="https://counter.theconversation.com/content/68637/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris North is a lecturer in the School of Physics and Astronomy at Cardiff University, and receives funding from the Ogden Trust and the Science and Technology Facilities Council.</span></em></p>The full moon is stunning – and this month it’ll be larger than normal. Do make it a reason to embrace the darkness and have a look.Chris North, Lecturer of Physics and Astronomy, Cardiff UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/682702016-11-08T20:53:15Z2016-11-08T20:53:15ZSupermoons are big and bright, but not as rare as the hype would suggest<figure><img src="https://images.theconversation.com/files/145081/original/image-20161108-16730-qa8ndt.jpg?ixlib=rb-1.1.0&rect=527%2C217%2C4229%2C2716&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Enjoy the full moon's glow.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/91467128@N08/14694185668">mstollenwerk</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>As an observational astronomer who teaches students about the behavior of the moon, I’m thankful for anything that inspires people to go out and look at the sky. For me it’s second nature to pay attention to the moon; when my son was born, I would take him out at night to observe with me, and one of his very first words was “moon.”</p>
<p>But I have mixed feelings about what’s being billed as the upcoming “super-supermoon.” Many astronomers do not like using the term because reports overhype the factors that make certain full moons unusual. Most of what you’ve likely read has probably misled you about what you can expect to see on Nov. 14 and just how rare this event is. Beautiful, yes. Worth looking up for, definitely. Once in a lifetime… that’s a bit overblown.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/144941/original/image-20161107-4718-1y7vtow.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/144941/original/image-20161107-4718-1y7vtow.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/144941/original/image-20161107-4718-1y7vtow.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=240&fit=crop&dpr=1 600w, https://images.theconversation.com/files/144941/original/image-20161107-4718-1y7vtow.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=240&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/144941/original/image-20161107-4718-1y7vtow.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=240&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/144941/original/image-20161107-4718-1y7vtow.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=302&fit=crop&dpr=1 754w, https://images.theconversation.com/files/144941/original/image-20161107-4718-1y7vtow.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=302&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/144941/original/image-20161107-4718-1y7vtow.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=302&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 moon’s phases as it revolves around the Earth.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Moon_phases_en.jpg">Orion 8</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>The moon’s cyclical phases</h2>
<p>Just about everyone is familiar with the moon’s changing appearance as it goes through its phases from crescent, to half-illuminated (first quarter), to gibbous, to full, and then back through gibbous, to half-illuminated (third quarter), to crescent, to new.</p>
<p>This pattern occurs because the moon orbits the Earth. When the moon is between the Earth and sun, it’s a new moon, and you don’t see it that day. When the moon is on the opposite side of the Earth from the sun we get a full moon as the sun’s light illuminates almost its entire face. The complete sequence of phases takes about the same amount of time as it does for the moon to orbit the Earth once – just about a month. </p>
<p>As the moon makes its monthly trip around our planet, it travels on an elliptical, not circular, path. Every object in the solar system orbits like this, including the Earth around the sun; over the course of the year, the Earth is sometimes closer to the sun and sometimes more distant. Same for the moon – sometimes it’s closer to us and sometimes farther away.</p>
<p>The changes are proportionally not large; at “perigee” (the closest it gets to the Earth) the moon’s approximately 10 percent closer to the Earth than at “apogee” (most distant point on its orbit). Over the year, the moon’s distance from Earth <a href="http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html">varies from around 222,000 to 253,000 miles</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/144944/original/image-20161107-4711-1rrj2jf.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/144944/original/image-20161107-4711-1rrj2jf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/144944/original/image-20161107-4711-1rrj2jf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=522&fit=crop&dpr=1 600w, https://images.theconversation.com/files/144944/original/image-20161107-4711-1rrj2jf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=522&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/144944/original/image-20161107-4711-1rrj2jf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=522&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/144944/original/image-20161107-4711-1rrj2jf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=655&fit=crop&dpr=1 754w, https://images.theconversation.com/files/144944/original/image-20161107-4711-1rrj2jf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=655&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/144944/original/image-20161107-4711-1rrj2jf.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=655&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 moon’s orbit is elliptical and changes over time.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Moon_apsidal_precession.png">Rfassbind</a></span>
</figcaption>
</figure>
<p><a href="https://eclipse.gsfc.nasa.gov/SEhelp/moonorbit.html">The time it takes the moon</a> to go from perigee to perigee (about 27.3 days) is shorter than the time it takes to go through a complete set of phases (about 29.5 days). Because these timescales are different, the phase at which perigee occurs varies. Sometimes perigee occurs when the moon is full, but it is just as likely for perigee to occur when the moon is in the first quarter phase, or any other. Whichever phase the moon is in when it’s at perigee will be the one that looks largest to us here on Earth for that month.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/145075/original/image-20161108-16718-1ncist6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/145075/original/image-20161108-16718-1ncist6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/145075/original/image-20161108-16718-1ncist6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/145075/original/image-20161108-16718-1ncist6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/145075/original/image-20161108-16718-1ncist6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/145075/original/image-20161108-16718-1ncist6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/145075/original/image-20161108-16718-1ncist6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/145075/original/image-20161108-16718-1ncist6.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">Two full moons as seen from Earth: at perigee on the left, at apogee on the right.</span>
<span class="attribution"><a class="source" href="http://apod.nasa.gov/apod/ap140908.html">Catalin Paduraru</a></span>
</figcaption>
</figure>
<p>At perigee, the moon can appear <a href="https://science.nasa.gov/news-articles/2016-ends-with-three-supermoons">14 percent larger and 30 percent brighter</a> than an apogee full moon. But this is complicated by the fact that our eyes play tricks on us and convince us the <a href="http://www.skyandtelescope.com/observing/moon-illusion-confusion11252015/">moon looks larger when it is near the horizon</a> than when it is higher in the sky. Every full moon will look big and bright whether it happens at perigee or apogee.</p>
<h2>So what’s a supermoon?</h2>
<p>The first time I heard the phrase “supermoon” was in 2011, and someone had to explain the suddenly in vogue term to me. People were using it to describe the full moon that happened to occur within an hour of perigee in March of that year. The moon’s perigee distance also varies a bit, and March 2011 was the moon’s closest perigee of that year.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/144952/original/image-20161107-4683-17xsos7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/144952/original/image-20161107-4683-17xsos7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/144952/original/image-20161107-4683-17xsos7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=849&fit=crop&dpr=1 600w, https://images.theconversation.com/files/144952/original/image-20161107-4683-17xsos7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=849&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/144952/original/image-20161107-4683-17xsos7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=849&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/144952/original/image-20161107-4683-17xsos7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1067&fit=crop&dpr=1 754w, https://images.theconversation.com/files/144952/original/image-20161107-4683-17xsos7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1067&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/144952/original/image-20161107-4683-17xsos7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1067&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 2013 supermoon as seen from Ireland.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/johnfinn/9125026108">John Finn</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>This was a somewhat rare event – a full moon occurring not just at perigee, but at the closest perigee of the year. But many people got the impression that this was an exceedingly unusual event, and rushed to see and capture images of this supposedly ultra-rare moon. Depending on how closely you require the full moon to occur to perigee in order to call it a supermoon, though, these events happen at least roughly once a year, and often more frequently.</p>
<p>Which brings us to this month’s much ballyhooed “super-supermoon.” News stories are hyping the upcoming full moon as a once-in-a-lifetime viewing opportunity. It’s true that the Nov. 14 full moon is the <a href="http://www.astronomy.com/observing/news/2016/11/theres-super-hype-for-this-months-super-moon">closest since 1948</a>, and the next time the full moon will be closer is in 2034.</p>
<p>But this month’s full moon is only 0.02 percent closer – a mere 41 miles! – than the March 2011 supermoon. These tiny distances make no noticeable difference in the moon’s appearance. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/144949/original/image-20161107-4694-1f5evl6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/144949/original/image-20161107-4694-1f5evl6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/144949/original/image-20161107-4694-1f5evl6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=533&fit=crop&dpr=1 600w, https://images.theconversation.com/files/144949/original/image-20161107-4694-1f5evl6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=533&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/144949/original/image-20161107-4694-1f5evl6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=533&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/144949/original/image-20161107-4694-1f5evl6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=670&fit=crop&dpr=1 754w, https://images.theconversation.com/files/144949/original/image-20161107-4694-1f5evl6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=670&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/144949/original/image-20161107-4694-1f5evl6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=670&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Get out there and enjoy this supermoon!</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Missouri-Daily-LIfe/26c430a53589446ea7ccd3368553f4be/1/0">AP Photo/Charlie Riedel</a></span>
</figcaption>
</figure>
<p>Please do go out and observe the November full moon. If you are good with photography, try to document that the moon does appear larger than the other months this year. Just be aware you’ll have other virtually equivalent opportunities to do so pretty much every year for the rest of your life. So don’t worry if you miss it. You can catch the supermoon next time around.</p><img src="https://counter.theconversation.com/content/68270/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Palma does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Full moons are good reason to look up – and the one on Nov. 14 is no exception. But here’s why you likely won’t see something shockingly different from other full moons you’ve observed over the years.Christopher Palma, Senior Lecturer and Associate Department Head for Undergraduate Programs in Astronomy & Astrophysics, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/482602015-09-29T05:23:48Z2015-09-29T05:23:48ZAfter the supermoon, comes the supertide<figure><img src="https://images.theconversation.com/files/96472/original/image-20150928-30964-awi6ue.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">..and high tides.</span> <span class="attribution"><span class="source">Paul J Martin / Shutterstock.com</span></span></figcaption></figure><p>The city of Plymouth, on England’s south coast, normally has fairly moderate tides. However this week it will have <a href="http://www.ntslf.org/tides/hilo?port=Plymouth">a 6m “supertide”</a> – the highest tide <a href="http://www.plymouthherald.co.uk/Flood-alert-highest-supertide-18-years-come/story-26210483-detail/story.html">in 18 years</a>. This comes just days after the celebrated <a href="https://theconversation.com/fact-over-fiction-on-the-apocalyptic-super-blood-moon-47916">“supermoon”</a>.</p>
<p>In fact, many locations along the UK, US and Australian coasts will experience their highest tides for tens of years around September 29 or 30. Coastal roads in Miami, for instance, have already <a href="http://www.miamiherald.com/news/local/community/miami-dade/miami-beach/article36784707.html">been closed</a> in anticipation of exceptional tides.</p>
<p>These high tides may bring water levels uncomfortably close to the tops of harbour walks and flood defences, emphasising the threat of rising sea levels. In the UK they are unlikely to be a major problem on their own unless they coincide with storms (a <a href="https://theconversation.com/been-flooded-recently-these-scientists-want-to-hear-from-you-41716">strong storm surge</a> has a greater impact than even the most exotic of tides). However in other areas, like in parts of America and the Pacific, no storms are necessary: these high tides on their own can lead to <a href="http://oceanservice.noaa.gov/facts/nuisance-flooding.html">nuisance flooding</a>.</p>
<h2>Why do we expect such extreme tides?</h2>
<p>Tides are controlled by changes in the position and alignment of the moon and sun relative to Earth. Every fortnight – at new moon or full moon – the Earth, sun and moon are in an approximately straight line as seen from space and the additional gravitational pull of the sun causes stronger tides, known as spring tides.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/budXQlGL8Dc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The Bay of Fundy on Canada’s Atlantic coast has the world’s highest tides.</span></figcaption>
</figure>
<p>Yet each month one set of spring tides is higher than the other. This is because tidal forces are strengthened when the moon is at “<a href="http://www.moonconnection.com/apogee_perigee.phtml">perigee</a>” and its elliptical orbit takes it closest to Earth. Tide-generating forces are also enhanced when the moon is directly overhead at the equator, part of a cycle lasting 27.2 days – a so-called “<a href="http://www.britannica.com/science/draconic-month">draconic month</a>”.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=416&fit=crop&dpr=1 600w, https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=416&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=416&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=523&fit=crop&dpr=1 754w, https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=523&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/96485/original/image-20150928-30999-j3j0bw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=523&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Elliptical orbits of: (A) the moon around the Earth; and (B) the Earth around the sun.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Tides can differ over the course of a year, as the Earth moves from its <a href="http://www.windows2universe.org/physical_science/physics/mechanics/orbit/perihelion_aphelion.html">closest (perihelion) to furthest (aphelion)</a> point from the sun and back. More important is the variation in the sun’s position north or south of the equator, which causes the seasons. The tide-generating forces are greatest at the equinoxes in March and September when the sun is directly overhead at the equator. Spring tides are always higher at these times of year. </p>
<h2>A perfect tide?</h2>
<p>Over periods longer than a year, very large spring tides occur when all the astronomical factors we have mentioned earlier coincide. </p>
<p>Two longer-term motions of the moon’s orbit around the Earth are important. These motions (<a href="http://csep10.phys.utk.edu/astr161/lect/time/precession.html">astronomers call them precessions</a>) are the reason we are seeing unusually large spring tides this year. </p>
<p>The first precession is known as the cycle of lunar perigee, and influences tides about every four to five years. The elliptical orbit of the moon around the Earth slowly moves in relation to the sun, completing a full circuit every 8.8 years. This means at either the March or September equinox approximately every 4.5 years the moon is both at its closest point to the Earth, and is also overhead at the equator.</p>
<p>The second precession is known as the <a href="http://onlinelibrary.wiley.com/doi/10.1029/2010JC006645/abstract">lunar nodal cycle</a> and is due to a very slow change in the moon’s orbit. Imagine the Earth’s orbit around the sun took place on an enormous sheet of glass – what astronomers call the ecliptic plane. The moon’s orbit cuts this surface at an angle of approximately 5 degrees. Over 18.6 years the moon’s orbit slowly rotates around so it cuts through the ecliptic plane in a different place. </p>
<p>One effect of this is to change how far above or below the equator the moon can reach in its orbit. In 2015 the moon is at the point where it deviates the least from the equator. This slightly increases the chances of the moon being directly overhead at the equator at any given point, and thus coinciding with the other factors that contribute to extreme tidal forces.</p>
<p>A lot of things have to fall in place at once to generate record-breaking tides and this year the cycle of lunar perigee and the lunar nodal cycle nearly perfectly coincide, resulting in some of the highest spring tides for decades. </p>
<hr>
<p><em>The authors help run the <a href="http://www.surgewatch.org/contribute-photos/">SurgeWatch</a> website and would welcome any photos of high tides during this period.</em></p><img src="https://counter.theconversation.com/content/48260/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ivan Haigh has received funding from the Natural Environment Research Council and the Engineering and Physical Sciences Research Council.</span></em></p><p class="fine-print"><em><span>Kevin Horsburgh receives funding from The Natural Environment Research Council and the Environment Agency.</span></em></p>This is what you get when a full moon, a perigee moon and the September equinox all happen at once.Ivan Haigh, Lecturer in Coastal Oceanography, University of SouthamptonKevin Horsburgh, Head of Marine Physics and Ocean Climate, National Oceanography CentreLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/479162015-09-25T02:58:13Z2015-09-25T02:58:13ZFact over fiction on the ‘apocalyptic’ super blood moon<figure><img src="https://images.theconversation.com/files/96166/original/image-20150925-16033-1h2z2f.jpg?ixlib=rb-1.1.0&rect=1522%2C146%2C4432%2C3552&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Dramatic, but not apocalyptic.</span> <span class="attribution"><span class="source">Stanimir G Stoev</span></span></figcaption></figure><p>For many people, the sight of the moon turning deep red – some would say blood red – during a <a href="https://theconversation.com/explainer-what-is-a-lunar-eclipse-32426">lunar eclipse</a> is a wonderful sight. And that’s precisely what many millions of sky gazers will be able to see this Sunday or Monday, depending on their location on Earth.</p>
<p>But for a dedicated few, this is a sign of something <a href="http://www.christianpost.com/news/blood-moon-2015-rumors-apocalypse-to-begin-at-moonrise-145466/">much more terrifying</a>: nothing less than <a href="http://www.christiantoday.com/article/blood.moon.this.september.could.be.biblical.sign.of.apocalypse.pastors.say/63472.htm">the apocalypse itself</a>.</p>
<p>Lunar eclipses are an impressive and visible reminder that the night sky isn’t a static backdrop but a dynamic show filled with worlds that move and interact. In this case, the moon’s orbit will take it directly behind the Earth, opposite the sun and into our shadow, which will carve out evermore of the moon’s face until it’s entirely dark.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/60953/original/tq5q6cxs-1412637172.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/60953/original/tq5q6cxs-1412637172.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/60953/original/tq5q6cxs-1412637172.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=417&fit=crop&dpr=1 600w, https://images.theconversation.com/files/60953/original/tq5q6cxs-1412637172.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=417&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/60953/original/tq5q6cxs-1412637172.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=417&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/60953/original/tq5q6cxs-1412637172.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=524&fit=crop&dpr=1 754w, https://images.theconversation.com/files/60953/original/tq5q6cxs-1412637172.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=524&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/60953/original/tq5q6cxs-1412637172.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=524&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>Or, at least, it would be if the Earth’s atmosphere wasn’t bending (refracting) light into that shadow region, known as the <a href="http://www.britannica.com/topic/umbra-eclipse">umbra</a>. After passing through so much air, the bluer colours are scattered out and all that remains is red. We see this effect in the reddening of the sunlight every sunrise and sunset. </p>
<p>In other words, this blood moon is nothing less than all the sunrises and sunsets of the Earth, reflected back at us from the surface of the moon. Sadly, this romanticism will be lost on a dedicated few who will instead greet it with fear as a portent of terrible events.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/96128/original/image-20150925-17103-1711k2y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/96128/original/image-20150925-17103-1711k2y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/96128/original/image-20150925-17103-1711k2y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/96128/original/image-20150925-17103-1711k2y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/96128/original/image-20150925-17103-1711k2y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/96128/original/image-20150925-17103-1711k2y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/96128/original/image-20150925-17103-1711k2y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/96128/original/image-20150925-17103-1711k2y.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">Various stages of a blood moon in April 2014.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/39873796@N06/14128055021/">R E Barber Photography</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Enter the tetrad: a rare event?</h2>
<p>This latest event marks the fourth lunar eclipse in a row with no partial eclipses to spoil the run. Such a run of eclipses is known as a <a href="http://science.nasa.gov/science-news/science-at-nasa/2014/27mar_tetrad/">tetrad</a>. While not uncommon – there have been <a href="http://eclipse.gsfc.nasa.gov/OH/OHtables/OH2014-Tab06.pdf">eight</a> such tetrad eclipses in the 21st century – they are unusual, with none between 1400 to 1900. </p>
<p>What makes this final of the four a little different is that it’s during a <a href="https://theconversation.com/check-out-the-years-biggest-and-brightest-moon-on-sunday-night-15129">super moon</a>. This is when the full moon occurs when the moon is closest to the Earth in its orbit, thereby appearing about 14% bigger and 30% brighter than when furthest from us.</p>
<p>The last time there was a <a href="http://www.nasa.gov/feature/goddard/nasa-scientist-sheds-light-on-rare-sept-27-supermoon-eclipse/">blood super moon</a> (or less poetically: a perigee lunar eclipse) was in 1982, with the next not until 2033.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/vKAw_wrIr5s?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>So this larger and more noticeably red moon will be the best for a generation or more, for those lucky enough to be able to see it.</p>
<h2>Apocalypse when?</h2>
<p>But not everyone is looking forward to the event. There are <a href="http://www.news.com.au/lifestyle/real-life/preppers-are-stockpiling-food-as-dreaded-september-28-blood-moon-apocalypse-nears/story-fnq2oad4-1227533200479">reports</a> from stores in the United States of panic buying in anticipation of the coming lunar eclipse, <a href="http://www.christiantoday.com/article/panic.buying.in.utah.as.mormon.preppers.get.ready.for.doomsday.later.this.month/64747.htm">stockpiling supplies</a> in the fear that this is the apocalypse. </p>
<p>So what is driving this fear of an otherwise natural, albeit particularly uncommon, lunar eclipse?</p>
<p>It seems to come from the fact that the previous lunar eclipses of the tetrad have fallen on dates of significance in the Jewish calendar. But that’s <a href="http://www.timeanddate.com/calendar/apocalypse.html">happened before</a> and the world didn’t end then.</p>
<p>Fuelling all this are two Christian ministers: Mark Blitz, who wrote the bestseller <a href="http://wndbooks.wnd.com/blood-moons/">Blood Moons: Decoding the Imminent Heavenly Signs</a>; and John Hagee, who wrote his own bestseller, <a href="http://www.jhm.org/Catalog/Product/S1244">Four Blood Moons</a>.</p>
<p>NASA scientists say there have been a number of recent blogs and posts online claiming the Earth will be hit by an asteroid between September 15 and 28, the date of the lunar eclipse.</p>
<p>But Paul Chodas, manager of NASA’s Near-Earth Object office at the Jet Propulsion Laboratory, said there was “<a href="http://www.jpl.nasa.gov/news/news.php?feature=4692">no existing evidence</a>” that an asteroid or any other celestial object would hit Earth anytime “over the next century”.</p>
<p>Now the asteroid claim has been dismissed, Blitz has reportedly turned his <a href="http://www.express.co.uk/news/weird/584602/Rare-Blood-Moon-September-huge-earth-destroying-earthquakes-prophets-warn-USA-pope">attention to earthquakes</a>. </p>
<h2>High tides and earthquakes</h2>
<p>These rumours have clearly frightened some believers, but how much truth is there that a lunar eclipse will trigger a devastating earthquake?</p>
<p>According to the evidence, a categorical “none”, says the <a href="http://www.earthquakes.bgs.ac.uk/research/earthquakeSunMoon.html">British Geological Society</a>, with studies showing the coincidence of earthquakes and the phases of the moon were entirely random.</p>
<p>That the moon has an effect on the Earth is undeniable; we can see that every day with the tides. The Earth itself will be squeezed in the same way, although with a barely noticeable rise as solid rock is less malleable than water.</p>
<p>Along with this Earth-tide, the seabed will also experience changing pressure from the weight of all the water above as the tides rise and fall. That this might be a trigger of earthquakes seems reasonable, and was thought to be so for a century, but the numbers just don’t add up.</p>
<p>For starters, the difference in the pressure on the rock caused by the tides is less than the normal tectonic forces that the plates experience in their slow migration around the Earth. More definitively, there’s simply no observed link between earthquake severity and the tide maximum.</p>
<p>It’s also worth keeping in mind that the only difference between a full moon and the blood moon is that the latter just happens to be passing through the Earth’s shadow and hence turns a spooky colour. Its actual distance from us (and hence apocalypse-inducing force that it could apply) is be the same. </p>
<p>Even though this lunar eclipse is occurring during a super moon the <a href="http://tidesandcurrents.noaa.gov/faq2.html#15">increase in tide height</a> from this closer moon is at most 10 centimetres so hardly an apocalyptic flood.</p>
<h2>Enjoy the view</h2>
<p>Thankfully it looks like the world isn’t about to end, and those lucky enough to be in the right place can sit back, relax and enjoy the lunar eclipse.</p>
<p>The phase where the Earth’s shadow begins to overlap the face of the moon will last three hours and 20 minutes. The blood moon will occur during totality, when the moon enters the deepest part of our shadow, the umbra, lasting one hour and 12 minutes.</p>
<p>For Europe and Africa, this means a very early start. For eastern-seaboard US and Canada, it will be much more reasonable viewing time. Australia will miss out on seeing the event, sadly.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/96338/original/image-20150927-17708-fx8vfr.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/96338/original/image-20150927-17708-fx8vfr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/96338/original/image-20150927-17708-fx8vfr.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=291&fit=crop&dpr=1 600w, https://images.theconversation.com/files/96338/original/image-20150927-17708-fx8vfr.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=291&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/96338/original/image-20150927-17708-fx8vfr.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=291&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/96338/original/image-20150927-17708-fx8vfr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=365&fit=crop&dpr=1 754w, https://images.theconversation.com/files/96338/original/image-20150927-17708-fx8vfr.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=365&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/96338/original/image-20150927-17708-fx8vfr.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=365&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">What time and date to see the lunar eclipse from various locations.</span>
<span class="attribution"><a class="source" href="http://www.timeanddate.com/eclipse/lunar/2015-september-28">The Conversation/timeanddate.com</a></span>
</figcaption>
</figure>
<p>There are plenty more time and date details to view the lunar eclipse from other locations are available from the <a href="http://www.timeanddate.com/eclipse/lunar/2015-september-28">timeanddate.com</a> website.</p>
<iframe width="100%" height="270" src="https://www.ustream.tv/embed/6539981?html5ui" allowfullscreen="" webkitallowfullscreen="" scrolling="no" frameborder="0" style="border: 0 none transparent;"></iframe><img src="https://counter.theconversation.com/content/47916/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alan Duffy is an astronomer at Swinburne University of Technology.</span></em></p>A rare super blood moon visible from parts of the Earth this month will delight those people lucky enough to see it. But why has this marvel of the solar system got some people so worried?Alan Duffy, Research Fellow, Swinburne University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/302692014-08-07T08:08:04Z2014-08-07T08:08:04ZSupermoon … or not so super?<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/55943/original/b36sf7yj-1407394920.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/55943/original/b36sf7yj-1407394920.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/55943/original/b36sf7yj-1407394920.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=354&fit=crop&dpr=1 600w, https://images.theconversation.com/files/55943/original/b36sf7yj-1407394920.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=354&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/55943/original/b36sf7yj-1407394920.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=354&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/55943/original/b36sf7yj-1407394920.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=445&fit=crop&dpr=1 754w, https://images.theconversation.com/files/55943/original/b36sf7yj-1407394920.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=445&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/55943/original/b36sf7yj-1407394920.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=445&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Is one full moon better than any other?</span>
<span class="attribution"><span class="source">Phil Hart</span></span>
</figcaption>
</figure>
<p>A beautiful full moon is set to rise this Sunday night, August 10. It will be spectacular and I encourage everyone to go outside and have a look. But the question is: will it be a supermoon? </p>
<p>Technically yes: by the definition that’s fallen into common usage, it will be a supermoon. By this I mean that the full moon will coincide with the moon being slightly closer to us, as it travels along its elliptical orbit around the Earth.</p>
<p>Will we notice that this moon is bigger and brighter than any other full moons to be seen this year? It might be nice to think so, but in all honesty it’s not really possible to spot the effect. </p>
<p>The moon is impressive as it is; being a little bit more impressive on odd occasions like this doesn’t make it stand out any more. But what it does do is give us the opportunity to think about our neighbour in space.</p>
<h2>What’s in a name?</h2>
<p>To set the record straight, the term “supermoon” comes from astrology. It was coined by <a href="http://www.astropro.com/features/articles/supermoon/">Richard Nolle</a> a “certified professional astrologer” in an article for Horoscope magazine in 1979. </p>
<p>Unfortunately, Nolle uses it to argue that this kind of moon will trigger cataclysmic events because of the extreme tidal forces at work. It won’t – the variations will bring about a tide that in most places is <a href="https://theconversation.com/check-out-the-years-biggest-and-brightest-moon-on-sunday-night-15129">only a few centimetres</a> higher than usual. </p>
<p>I must admit though, that supermoon has a better ring to it than perigee moon, which is the scientific expression.</p>
<p><a href="http://astronomy.swinburne.edu.au/cms/astro/cosmos/p/Perigee">Perigee</a> denotes the point in the moon’s orbit when it passes closest to Earth. It brings the moon about 50,000km closer than at <a href="http://astronomy.swinburne.edu.au/cosmos/A/Apogee">apogee</a> when the moon passes furthest from Earth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/55945/original/wfprgc7v-1407395479.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/55945/original/wfprgc7v-1407395479.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/55945/original/wfprgc7v-1407395479.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=373&fit=crop&dpr=1 600w, https://images.theconversation.com/files/55945/original/wfprgc7v-1407395479.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=373&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/55945/original/wfprgc7v-1407395479.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=373&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/55945/original/wfprgc7v-1407395479.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=468&fit=crop&dpr=1 754w, https://images.theconversation.com/files/55945/original/wfprgc7v-1407395479.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=468&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/55945/original/wfprgc7v-1407395479.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=468&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 full moon occurs at various distances from Earth across the year.</span>
<span class="attribution"><span class="source">Museum Victoria/MICA</span></span>
</figcaption>
</figure>
<p>In the graph above, I have plotted the distance of each full moon throughout the year and you can see that this month’s full moon, at a distance of 353,552km, will be the closest for the year. </p>
<p>It just beats out last month’s by about 800km and it is almost 58,000km closer than the January full moon. Sounds impressive, right? </p>
<p>This change in distance, of about 14%, compares the perigee moon of August to the apogee moon of January. Not only are we relying on memory but the moon already looks big in the sky, so it’s quite a small relative change to notice.</p>
<p>Furthermore, most of the full moons we see across the year occur somewhere between these two extremes. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/55946/original/6f9m45wk-1407395627.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/55946/original/6f9m45wk-1407395627.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/55946/original/6f9m45wk-1407395627.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=599&fit=crop&dpr=1 600w, https://images.theconversation.com/files/55946/original/6f9m45wk-1407395627.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=599&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/55946/original/6f9m45wk-1407395627.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=599&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/55946/original/6f9m45wk-1407395627.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=752&fit=crop&dpr=1 754w, https://images.theconversation.com/files/55946/original/6f9m45wk-1407395627.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=752&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/55946/original/6f9m45wk-1407395627.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=752&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 supermoon of 2011 compared to an ordinary full moon.</span>
<span class="attribution"><span class="source">Marco Langbroek</span></span>
</figcaption>
</figure>
<p>Of course if the moon is closer, then it’s also brighter. Sunday night’s full moon will be about 30% brighter than the one from January. But again, the moon is already the brightest object in the night sky, so spotting a difference looking at the moon is nigh impossible.</p>
<h2>Lunar myths</h2>
<p>The supermoon seems to be one of those stories that will just continue to hang around. Like the folklore that <a href="https://theconversation.com/mondays-medical-myth-hospitals-get-busier-on-full-moons-5383">hospitals are busier</a> on nights of a full moon or that the moon affects us in <a href="http://www.scientificamerican.com/article/lunacy-and-the-full-moon/">weird ways</a>.</p>
<p>There is one moon phenomenon that is not yet explained and that is the moon illusion. It’s the idea that most of us perceive the moon as being bigger when it’s on the horizon compared to when it’s high up above in the sky. </p>
<p>When you are looking at the moon on Sunday night, measure it by putting your thumb in front of it or roll up a piece of paper to match the moon’s diameter as it appears large upon the horizon. Then do the same when the moon is higher in the sky and you’ll see that the change in size is all in your mind. </p>
<p>The <a href="http://en.wikipedia.org/wiki/Ebbinghaus_illusion">Ebbinghaus illusion</a> and the <a href="http://psychology.about.com/od/sensationandperception/ig/Optical-Illusions/The-Ponzo-Illusion.htm">Ponzos illusion</a> are often used to explain it, but researchers from the Susquehanna University, Pennsylvania <a href="http://www.technologyreview.com/view/509966/moon-illusion-new-theory-reignites-debate-over-why-moon-appears-larger-near-the-horizon/">have put forward</a> that it may stem from us perceiving that the moon is closer on the horizon, while at the same time our binocular vision is telling us its not.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ehulHtKfpuM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Full moon silhouettes by Mark Gee.</span></figcaption>
</figure>
<p>If you want to see a truly magical moon, then go no further than the video above. It is <a href="http://markg.com.au/2013/01/full-moon-silhouettes/">real time footage</a> of the moon captured from New Zealand with a super telephoto lens and a great deal of creativity. Can the moon really get more stunning?</p><img src="https://counter.theconversation.com/content/30269/count.gif" alt="The Conversation" width="1" height="1" />
A beautiful full moon is set to rise this Sunday night, August 10. It will be spectacular and I encourage everyone to go outside and have a look. But the question is: will it be a supermoon? Technically…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/292272014-08-07T05:21:39Z2014-08-07T05:21:39ZBig moon rising: go and have a look, but don’t be fooled into thinking it’s all that super<figure><img src="https://images.theconversation.com/files/54490/original/vrb99ptt-1405983867.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Just another moonrise, that's all.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/blingrocks/5569466262">blingrocks</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The year’s biggest “supermoon” will rise on August 10. <a href="http://www.reuters.com/news/pictures/slideshow?articleId=USRTR3YEBL">Like last time</a>, there will be many pictures trying to showoff the “over-sized” moon. But I don’t think it deserves so much attention.</p>
<p>At 7.09pm BST that evening, the moon will be at its closest point to the Earth. This is because of its slightly eccentric orbit.</p>
<p>The distance between the moon’s centre and the Earth’s centre will be 356,896 km, as opposed to an average distance of 384,400 km. The moon will be full all night – that is, fully illuminated by the sun – so you won’t need to look at a precise time to “experience” the phenomenon.</p>
<p>As it happens, the moon is at its closest once every month, but it is only when the closest approach coincides with the full moon that people make a fuss. Supermoon is a term coined by an astrologer about 30 years ago, and it has caught the popular imagination more recently.</p>
<p>It is a neat term – like <a href="https://theconversation.com/how-earths-devastating-supervolcanoes-erupt-21943">supervolcano</a>. A supervolcanic eruption somewhere in the world happens on average only every 50,000 years or so, produces at least ten times more ash than any volcano in the past millennium, and could blot out so much sunlight that plants would cease to grow for months on end. A supermoon is defined as a full moon occurring during the tenth of its orbit that is closest to the Earth. On average this happens at least once a year – there are three in a row in 2014 – and scarcely looks special at all.</p>
<p>I am in favour of people being encouraged to go out and look at the moon, but not of urging them to do so <a href="http://www.open.edu/openlearn/moonmyths">under false pretences</a>. A <a href="http://earthsky.org/space/what-is-a-supermoon">supermoon is a curiosity</a>, and has no measured correlation with natural disasters such as storms and earthquakes. If you take a long-term average, ocean tides on the coast will be fractionally larger when there is a supermoon. But other effects that can increase or depress tidal range, such as wind speed and direction, or changes in atmospheric pressure, are more than enough to swamp the tiny difference between normal tide and supermoon tide on any day.</p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/54489/original/wymrcxr6-1405983526.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/54489/original/wymrcxr6-1405983526.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=790&fit=crop&dpr=1 600w, https://images.theconversation.com/files/54489/original/wymrcxr6-1405983526.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=790&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/54489/original/wymrcxr6-1405983526.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=790&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/54489/original/wymrcxr6-1405983526.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=993&fit=crop&dpr=1 754w, https://images.theconversation.com/files/54489/original/wymrcxr6-1405983526.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=993&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/54489/original/wymrcxr6-1405983526.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=993&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
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<span class="attribution"><a class="source" href="http://xkcd.com/1394/">XKCD</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
</figcaption>
</figure>
<p>If you were to measure the moon’s apparent diameter on the night of a supermoon, it would be less than a tenth more than the average. You aren’t going to notice this just by looking. </p>
<p>Other effects, such as the well-known “moon illusion”, which makes the moon look larger when it is near the horizon, will dominate. Its size in the sky is not really any bigger, it just looks bigger because you subconsciously compare it with other distant objects. When the moon is high in the sky there’s nothing to compare it with, so it seems smaller – adrift in a sea of black. </p>
<p>You won’t notice brighter moonlight either, unless you go out expecting to be dazzled and allow yourself to be <a href="http://www.dailymail.co.uk/news/article-2690218/The-summer-supermoons-arrives-Stunning-sights-world-lunar-surface-appears-bigger-brighter-usual.html">fooled by the hype</a>.</p>
<p>So if you happen to see the supermoon, it will seem large because it will be right on the horizon. Because of the time of year it will stay fairly low all night. By all means go out and enjoy it – but please don’t kid yourself that it is anything out of the ordinary.</p>
<hr>
<p><em>Next, read this: <a href="https://theconversation.com/moons-gravity-alone-cannot-create-the-worlds-largest-tides-22033">Moon’s gravity alone cannot create the world’s largest tides</a></em></p><img src="https://counter.theconversation.com/content/29227/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Rothery 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>The year’s biggest “supermoon” will rise on August 10. Like last time, there will be many pictures trying to showoff the “over-sized” moon. But I don’t think it deserves so much attention. At 7.09pm BST…David Rothery, Professor of Planetary Geosciences, The Open UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/151292013-06-20T20:37:29Z2013-06-20T20:37:29ZCheck out the year’s biggest and brightest moon on Sunday night<figure><img src="https://images.theconversation.com/files/25877/original/k88mjgn2-1371685729.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Brace yourself for the most super supermoon of 2013 this weekend - but how exactly does the moon appear to change size?</span> <span class="attribution"><span class="source">Marianne Klock</span></span></figcaption></figure><p>This Sunday night, June 23, at precisely 9.33pm AEST, the full moon becomes a “<a href="http://science.nasa.gov/science-news/science-at-nasa/2012/02may_supermoon/">supermoon</a>” – an especially bright full moon.</p>
<p>This extra brightness occurs because the moon is closer to Earth than normal. The coincidence of a close moon when “full” only happens a few times a year but some supermoons are closer - and hence brighter - than others. This weekend’s supermoon is the closest, and most “super”, for 2013.</p>
<p>So, what time is best to see the supermoon? </p>
<p>Thanks to a curious psychological effect called the <a href="http://www.lhup.edu/%7Edsimanek/3d/moonillu.htm">Moon Illusion</a>, objects in the sky appear larger just above the horizon than when high in the sky. The moon will rise above the horizon at 5.07pm (AEST) in Melbourne just after the sun sets. So even though the moon is at it’s closest point four hours later, it will be most impressive as low on the horizon as possible.</p>
<h2>Why does the moon come closer?</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/25879/original/jxb4q9q7-1371686205.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/25879/original/jxb4q9q7-1371686205.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/25879/original/jxb4q9q7-1371686205.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/25879/original/jxb4q9q7-1371686205.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/25879/original/jxb4q9q7-1371686205.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/25879/original/jxb4q9q7-1371686205.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/25879/original/jxb4q9q7-1371686205.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/25879/original/jxb4q9q7-1371686205.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>
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<span class="attribution"><span class="source">NASA/Bill Ingalls</span></span>
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<p>The moon moves around Earth in its orbit, tracing out a squashed circle called an ellipse. Unlike a circular line which is always the same distance from the centre, an ellipse is closer to the centre at certain times. </p>
<p>When closest, the moon will be 356,991km away from us but this is actually 50,000km closer than when it’s furthest away. Those 50,000km means the moon will be 14% wider (and 30% brighter). The change in size might be hard to notice but the brightness won’t be! </p>
<p>A possible side-effect of a closer moon is that it can make the tides higher. Fortunately, even at the closest point the tide will only be about one centimetre higher (although unusually shaped local shores might have tides as much as 15cm) so there is little risk of flooding.</p>
<p>As the moon moves in its month-long orbit around the Earth, the side we see will be lit by different amounts by the sun. We call this a change in the “phase” of the moon. When the sun, Earth and moon lie in a straight line, the moon reflects sunlight from its entire surface to us and we see it as a “full” moon. </p>
<p>A fortnight later the moon lies between the sun and Earth with the surface facing us in shadow, we call this a “new” moon. </p>
<h2>The Moon Illusion</h2>
<p>The illusion is most obvious for the moon but also happens for any distant object in the sky (it would happen for the sun but staring at this isn’t a good idea). This effect has been studied for thousands of years with <a href="http://en.wikipedia.org/wiki/Aristotle">Aristotle</a> writing about it in 350BCE.</p>
<p>To check this is an illusion – and not the moon shrinking as it moves in the sky – hold out your thumb at arms length and cover the moon when it’s just risen. Note how much your thumb blocks. Then repeat this when the moon is high in the sky. You should find that the same amount of thumb covers the moon, so it really isn’t changing in size.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/49RztN4Bqu0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">But if you can’t wait until Sunday, you can watch an explanation here.</span></figcaption>
</figure>
<p>Astronomers and psychologists are still at odds about what’s behind the illusion. One theory is distant buildings can act as a reference object, making the moon seem larger (also known as an <a href="http://en.wikipedia.org/wiki/Ebbinghaus_illusion">Ebbinghaus Illusion</a>). Yet pilots see the Moon Illusion when flying with only shapeless clouds below, removing any reference point. Another idea relies on our brain being tricked by distant objects seemingly coming together in a <a href="http://en.wikipedia.org/wiki/Ponzo_illusion">Ponzo Illusion</a>. </p>
<p>But <a href="http://www.lhup.edu/%7Edsimanek/3d/moonillu.htm">most suggest</a> it is inbuilt in how humans see the world: through evolution, our brains are hardwired to pay more attention to those things in front of us than above (it’s likely that fewer cavemen were attacked by birds than by wolves). So objects in front of us appear larger in our attention. </p>
<p>It’s important to note that if you look at the rising moon with a tilted head (or even upside down!) the illusion isn’t quite as unnaturally large. This might look a little strange to other people but you could get away with it under the guise of the urban legend that <a href="https://theconversation.com/mondays-medical-myth-hospitals-get-busier-on-full-moons-5383">more people act crazy under a full moon</a>.</p>
<p><em>Check the time for your local moonrise <a href="http://www.timeanddate.com/worldclock/moonrise.html">here</a> and details about future supermoons <a href="http://earthsky.org/tonight/is-biggest-and-closest-full-moon-on-june-23-2013-a-supermoon">here</a>.</em></p><img src="https://counter.theconversation.com/content/15129/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alan Duffy is affiliated with ICRAR at the University of Western Australia and the Australian Research Council Centre of Excellence for All-sky Astrophysics.</span></em></p>This Sunday night, June 23, at precisely 9.33pm AEST, the full moon becomes a “supermoon” – an especially bright full moon. This extra brightness occurs because the moon is closer to Earth than normal…Alan Duffy, Postdoctoral Research Associate of Astronomy, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.