In #Astrophotography, star trails are a type of photograph that utilizes long-exposure times to capture the apparent motion of stars in the night sky due to the rotation of the Earth.
A star trail photograph shows individual stars as streaks across the image, with longer exposures resulting in longer streaks. Typical exposure times for a star trail range from 15 minutes to several hours, requiring a ‘bulb’ setting on the camera to open the shutter for a longer period than is normal. Star trails have been used by professional astronomers to measure the quality of observing locations for major telescopes.
How To: Star trail photographs are captured by placing a camera on a tripod, pointing the lens toward the sky, and allowing the shutter to stay open for a long period of time.
Star trails are considered relatively easy for amateur astrophotographers to create. Photographers generally make these images by using a SLR camera with its lens focus set to infinity. A cable release allows the photographer to hold the shutter open for the desired amount of time.