Satellite trail
A satellite trail is a line on a night-sky photograph left by sunlight reflecting off an orbiting satellite.
A satellite trail appears on long-exposure photographs of the night sky when a satellite passes through the field of view. Satellites shine because they reflect sunlight, so they are seen mainly in the hours after dusk and before dawn, when the sky is dark but the satellite, high above, is still in sunlight.
It is easy to confuse satellite trails with meteors. Satellites move slowly and steadily, taking minutes to cross the sky, and their trails are usually of even brightness and width. Some flash as they tumble. Meteors are much faster, lasting less than a second, and their trails often brighten and fade and taper at the ends. Aircraft show coloured, blinking lights.
The number of satellites has grown rapidly since 2019, with large networks of internet satellites launched in their thousands. They now cross many astronomical images, which concerns astronomers who study faint objects, including those searching for near-Earth asteroids.
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Level: Explorer Ages 10 and up