Long Exposure Photography

These two pictures were taken by Amy, while a GSCE Astronomy student in Yr 10. She kept the camera very still (on a tripod) and kept the shutter open for a long time.

The length of the sidereal day was calculated using these photos. Knowing the length of the exposure, and measuring the angle through which the stars have moved (actually how much the Earth has rotated), gave a value for the sidereal day. It should be 23 hours 56 minutes. The main uncertainty in this experiment is measuring the angle correctly.