As the Earth spins on its axis, the sky seems to rotate around us. This motion, called diurnal motion [
http://antwrp.gsfc.…], produces the beautiful concentric trails traced by stars during time exposures. In the middle of the picture is the North Celestial Pole [
http://solar.physic…] (NCP), easily identified as the point in the sky at the center of all the star trail arcs. The star Polaris [
http://antwrp.gsfc.…], commonly known as the North Star [
http://en.wikipedia…], made the very short bright circle near the NCP. Full circle star trails are pictured over Vienna, Austria [
http://www.cia.gov/…]. This image [
http://homepage.uni…pwafoxe.htm ], a relatively short exposure followed by a digital trick, could not have been taken during a single night because 24-hours are needed for one full rotation, and the Sun is sure [
http://antwrp.gsfc.…] to dominate the frame at some time.
Explanation
As the Earth spins on its axis, the sky seems to rotate around us. This motion, called diurnal motion [
http://antwrp.gsfc.…], produces the beautiful concentric trails traced by stars during time exposures. In the middle of the picture is the North Celestial Pole [
http://solar.physic…] (NCP), easily identified as the point in the sky at the center of all the star trail arcs. The star Polaris [
http://antwrp.gsfc.…], commonly known as the North Star [
http://en.wikipedia…], made the very short bright circle near the NCP. Full circle star trails are pictured over Vienna, Austria [
http://www.cia.gov/…]. This image [
http://homepage.uni…pwafoxe.htm ], a relatively short exposure followed by a digital trick, could not have been taken during a single night because 24-hours are needed for one full rotation, and the Sun is sure [
http://antwrp.gsfc.…] to dominate the frame at some time.
Explanation
