This image from April 27 shows a series of tornadoes forming over Alabama and Mississippi. Captured from a satellite orbiting located at a fixed location above Earth, images like these help track trends in weather patterns. Another set of polar-orbiting satellites are useful for long-term forecast predictions. NASA Earth Observatory hide caption

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NASA engineer Ernie Wright looks on as the first six primary mirror segments for the James Webb Space Telescope are prepped to begin final cryogenic testing at NASA's Marshall Space Flight Center. The telescope will have 18 primary mirror segments. David Higginbotham/NASA hide caption

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An artist's depiction of NASA's Spirit rover on the surface of Mars. Spirit became unresponsive in March 2010. NASA announced it had ended attempts to communicate with the rover on May 24, 2011. NASA hide caption

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Framed in the doors of the Kennedy Center's Vehicle Assembly Building, the crawler begins the long journey toward Launch Pad 37B with space shuttle Discovery in April 2005. This enormous cross between a tank and a cargo ship is the largest self-powered land vehicle in the world. NASA hide caption

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A satellite image shows a field of what may be buried pyramid sites in Egypt. Courtesy of DigitalGlobe Images hide caption

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