Star trail
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A star trail is a type of photograph that uses long exposure times to capture diurnal circles, the apparent motion of stars in the night sky due to Earth's rotation. A star-trail photograph shows individual stars as streaks across the image, with longer exposures yielding longer arcs. The term is used for similar photos captured elsewhere, such as on board the International Space Station and on Mars.
All the stars in the night sky appear to circle the celestial pole (the south pole in this photo). Over a period of several hours, this apparent motion leaves star trails.
Star trail photographed from Mount Wellington, Tasmania. Aurora australis visible in the background.
Star trail photography on salt lake in Lut desert in Iran
Star trails photographed from the International Space Station in low Earth orbit at an angle that makes the trails almost vertical instead of circular.
Long-exposure photography
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Long-exposure, time-exposure, or slow-shutter photography involves using a long-duration shutter speed to sharply capture the stationary elements of images while blurring, smearing, or obscuring the moving elements. Long-exposure photography captures one element that conventional photography does not: an extended period of time.
A long-exposure photograph of a street in Carson, California, 1986. The trails along the street are from headlights and taillights, while the circles in the sky are from a police helicopter.
The central square of Rothenburg ob der Tauber, Germany, during blue hour. Notice how a long exposure blurs moving vehicles and pedestrians while buildings retain sharp focus.
In this 45-minute exposure taken on a dark clear night at Paranal Observatory, the stars leave trails as they appear to revolve around the south celestial pole (left), due to Earth's rotation.
Long-exposure photograph of a break in pool.