Star trails over Earth -

Star trails over Earth Today’s Image of the Day from NASA Earth Observatory features a compilation of photographs taken by astronaut Don Pettit while he was onboard the International Space Station (ISS) in April of 2012. 

According to NASA, the composite was created from more than 72 long-exposure photographs taken over several minutes as the ISS. traveled over the Caribbean Sea, across South America, and over the South Atlantic Ocean. The National Aeronautics and Space Administration is an independent agency of the U.S. federal government responsi

Star trails over Earth In a blog post, Pettit explained that long-exposure picturble for the civilian space program, as well as aeronautics and space from the ISS show star trails as circular arcs, with the center of rotation being the poles of the station.

“My star trail images are made by taking a time exposure of about 10 to 15 minutes,” wrote Pettit. “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 image captures both natural and artificial lights that appear to astronauts as they pass over the night side of Earth. For example, cities appear as pale yellow-white streaks.

Image Credit: NASA Earth Observatory 

By Chrissy Sexton, Staff Writer

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