Stars don't last forever. Occasionally, a star bigger than our Sun will end its life in a huge explosion, called a <a href="/the_universe/supernova.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">supernova</a>. The center of the star collapses in less than a second, blowing away the outer layers of the star. There are many beautiful images of supernova remnants, the expanding shell of gas made up of the outer layers of the original star. This image is the Vela Supernova Remnant.<p><small><em>Image courtesy of the Anglo-Australian Observatory/Royal Observatory Edinburgh</em></small></p>As permafrost thaws, the land, atmosphere, water resources, ecosystems, and human communities are affected. Coastal areas and hillsides are vulnerable to erosion by thawing of permafrost. Thawing permafrost also causes a positive feedback to global warming, as carbon trapped within the once-frozen soils is released as <a href="/physical_science/chemistry/methane.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">methane</a>, a powerful <a href="/earth/climate/cli_greengas.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">greenhouse gas</a>. Watch the NBC Learn video - <a href="/earth/changing_planet/permafrost_methane_intro.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">Thawing Permafrost and Methane</a> to find out more.<p><small><em>Image courtesy of the USGS</em></small></p>Lunar eclipses are special events that only occur when certain conditions are met. First of all, the Moon must be in <a href="/the_universe/uts/moon3.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">full phase</a>. Secondly, the <a href="/sun/sun.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">Sun</a>, <a href="/earth/earth.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">Earth</a> and <a href="/earth/moons_and_rings.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">Moon</a> must be in a perfectly straight line. If both of these are met, then the Earth's shadow can block the Sun's light from hitting the Moon. The reddish glow of the Moon is caused by light from the Earth's limb scattering toward the Moon, which is reflected back to us from the Moon's surface.<p><small><em>Image credit - Doug Murray, Palm Beach Gardens, Florida</em></small></p>This historic image is the first ever taken from a spacecraft in orbit about <a href="/mercury/mercury.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">Mercury</a>, the innermost planet of the solar system. Taken on 3/29/2011 by <a href="/space_missions/robotic/messenger/messenger.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">MESSENGER</a>, it shows numerous craters across the <a href="/mercury/Interior_Surface/Surface/surface_overview.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">surface</a> of the planet. Temperatures there can reach over 800F because Mercury is so close to the Sun and rotates so slowly. MESSENGER entered orbit around Mercury earlier in March 2011.<p><small><em>NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington</em></small></p>The <a href="http://www.windows2universe.org/earth/Atmosphere/tornado/fujita.html">EF-5</a> <a href="http://www.windows2universe.org/earth/Atmosphere/tornado.html">tornado</a> that hit El Reno, Oklahoma on May 31st, 2013 was the widest ever recorded in the US, according to the National Weather Service in Norman Oklahoma. The tornado, which remained on the ground for 40 minutes and reached 2.6 miles across (4.2 km), took the lives of 18 people including storm chasers Tim Samaras, Paul Samaras and Carl Young.<p><small><em>Image courtesy of National Weather Service, Norman Oklahoma</em></small></p>Scientists are concerned that melting Arctic sea ice will increase the amount of fresh water in the <a href="/earth/polar/arctic_currents.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">Beaufort Gyre</a>, which could spill out into the Atlantic and cause major climate shifts in North America and Western Europe. Watch the <a href="/earth/changing_planet/freshwater_arctic.html&edu=elem&dev=1/k=/h/neptune/=/X-rays">Changing Planet: Fresh Water in the Arctic video</a>.<p><small><em> Courtesy of Jack Cook, WHOI (<a href="http://www.whoi.edu">Woods Hole Oceanographic Institute</a>)</em></small></p>


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