<p><strong>The <a href="http://news.nationalgeographic.com/news/2012/05/120505-supermoon-closest-earth-tides-disasters-space-science-tonight/">supermoon</a> hangs heavy over the Temple of Poseidon on Cape Sounion, south of <a href="http://travel.nationalgeographic.com/travel/city-guides/athens-greece/">Athens</a>, around twilight on Saturday evening.</strong></p><p>Due to the moon's egg-shaped orbit, our natural satellite is at perigee—its closest approach to Earth—about once a month. &nbsp;The term "supermoon" was coined in 1979 to describe a <a href="http://science.nationalgeographic.com/science/space/solar-system/full-moon-article.html">full moon</a> that coincides with perigee. (Apogee, when the moon is farthest from us, also occurs on a roughly monthly schedule.)</p><p>At its closest on Saturday, the moon was 221,801 miles (356,955 kilometers) from our planet—and just minutes away from of the official full moon phase, at 11:35 p.m. ET.</p><p>"As a consequence, this translates into it appearing as much as 16 percent bigger and 30 percent brighter than other full moons of 2012—not a huge amount, but definitely noticeable," said Geza Gyuk, an astronomer at the<a href="http://www.adlerplanetarium.org/"> Adler Planetarium</a> in Chicago.</p><p><em></em></p><p><em>—With reporting by Andrew Fazekas</em></p>