In the 15 years since its December 1995 launch, the SOHO spacecraft has doubled the number of comets sighted in the previous 300 years. Alex Lutkus/NASA/ESA hide caption

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The inner four planets of the Gliese 581 system orbit the host star, a red dwarf 20 light-years from Earth, in this rendering from a National Science Foundation artist. The planet in the foreground has a 37-day orbit and, like Earth, is far enough from the star for liquid water to exist. Lynette Cook/via NASA hide caption

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Brian May wrote "We Will Rock You," "I Want It All," "Fat Bottomed Girls" and "Tie Your Mother Down," among other Queen hits. courtesy of Queen hide caption

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The moon appears red during a lunar eclipse in the Qatari capital of Doha, 28 August 2007. It's going to happen again tonight, and be visible across North America. Karim Jaafar/AFP/Getty Images hide caption

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A picture from NASA's Hubble Space Telescope of the dwarf planet Pluto. Astronomer Michael Brown explains his role in demoting the planet in his new book, How I Killed Pluto And Why It Had It Coming. Anonymous/NASA hide caption

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The SpaceX Falcon 9 rocket lifts off Wednesday from the Cape Canaveral Air Force Station in Florida. John Raoux/AP hide caption

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