Astronaut Don Pettit created this image of star trails as seen from the International Space Station approximately 240 miles above Earth. He explains, "My star trail images are made by taking a time exposure of about 10 to 15 minutes. However, with modern digital cameras, 30 seconds is about the longest exposure possible, due to electronic detector noise effectively snowing out the image. To achieve the longer exposures I do what many amateur astronomers do. I take multiple 30-second exposures, then 'stack' them using imaging software, thus producing the longer exposure." The above picture combines 18 such exposures.
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