And from Bill Coley's camera...

A Trail to the Stars

A "star trail" image depicts the movement of stars in the sky as the earth rotates on its axis, movement that is caused by the earth's movement, not the stars'. To produce this image, I mounted my camera to a tripod and then set the camera to take 270 30-second exposures, one right after the other; the process took 2-1/2 hours. Because the camera is stationary on the tripod, the house and barn don't move, but the stars do, which creates the arcs. A computer program then assembles the 270 images into the single image you see here.