wow very nice!!! Can you explain your "stacked" thing? I'm a bit confused :/

Great shot.
Amanda have a look here;
http://www.diyphotography.net/your-complete-guide-for-photographing-star-trails
and a link to StarStax, which works on the Mac
http://www.markus-enzweiler.de/software/software.html

Thanks Amanda& Friiskiwi - Stacked shots are multiples of shots from the same spot. Just think of the stacks as all of the photos placed on top of one another. A 'star-trails' program then just blends all of these images into one and with any luck, the only movement is the position of the stars, hence the 'trails'

amazing

MnMCarta... it's basically adding layers when people chop

Actually - that is a rather ignorant view. It has Nothing to do with chopping, it is overlaying the same image multiple times.

172 stacked x30 ha ya that ain't chopping but it sure is a cool affect.