Proxima Centauri lies in the constellation of Centaurus (The Centaur), just over four light-years from Earth. Although it looks bright through the eye of Hubble, Proxima Centauri is not visible to the naked eye. ESA/Hubble & NASA hide caption

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With this shot of Mount Fuji, astronaut Scott Kelly tweeted, "your majesty casts a wide shadow!" Scott Kelly/NASA hide caption

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Astronaut's Photos From Space Change How We See Earth

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NASA astronaut Scott Kelly takes a selfie inside the cupola, a special module that provides a 360-degree view of Earth. Kelly and Russian cosmonaut Mikhail Kornienko have spent nearly a year aboard the International Space Station. NASA hide caption

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In this composite image, the sun has reached its northernmost point in Earth's sky, marking a season change and the first solstice of the year 2004. NASA/ESA hide caption

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Do You Really Know Why Earth Has A Solstice?

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Earth has been many different planets in its long history — and could be more. Some imaginary views are shown here. Top (from left): a water world before large-scale continents had formed; a "snowball" Earth phase with extreme glaciation; and a world shrouded in smoke after a large asteroid impact. Bottom: Earth today; Earth losing its oceans as the sun becomes hotter; and a final scorched Earth. Courtesy of Don Brownlee, University of Washington hide caption

toggle caption Courtesy of Don Brownlee, University of Washington