For astronauts on board the International Space Station, most of the year they travel a path that crisscrosses over where Earth is in daytime and where it is night, and as a result they see 16 sunrises and sunsets every day. But twice a year, around the winter and summer solstices, the space station's orbital pattern tracks what is known as the terminator -- the line on Earth that separates day from night. During those times, the astronauts experience constant twilight. Astronaut Don Pettit said this means that he'll see day if he looks to one side and night when he looks to the other.
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