Rooftop Rotations

This 40-minute star trail exposure was taken from my rooftop on the night of Wednesday, October 13, 2010 in Cedar Rapids, Iowa. The exposure, aimed at Polaris, the North Star, was started at 8:40 PM. The effect of circular star trails such as this are created as a result of the rotation of the Earth. Polaris appears fixed in the sky as it is nearly in line with Earth's polar axis. This photograph was shot at f/8, with an 18mm focal length and 640 ISO.