Comet C/2009 P1 (Garradd) - 2012 March 19 - 64 x 32s ISO6400
A modified stacking process keeps the comet or asteroid fixed while everything else moves past - no need to try to track the comet
Important to have regular intervals between shots to get smooth trails - here 32s exposures were initiated every 35s, using a Canon timer
This is a telescopic view. The trails here are not due to the Earth's rotation but because the comet moved in front of the stars.
The comet does not have a dust tail but the blue tail just visible is an ion tail: charged particles blown away by the solar wind. It therefore points away from the Sun, like all comet tails.
This image won me a Highly Commended in the 2012 Astrophotographer of the Year competition at Greenwhich.