I was going to go out into the depths of the countryside last night and shoot a star movement timelapse. Instead I set the camera up down the back of the apartment complex green (in the wild grass). I figured I would do a test run first.
Here’s the result of shooting 13″ exposures at ISO800 (f5.6) on my 40D. I could’ve used the 5D with the 24 @ f2.8 with a lower ISO, but I was loathe to leave it out there just in case.

The movie is up on Vimeo.

Night Timelapse test from Sean McCormack on Vimeo.

With help from John Beardsworth on Twitter, I was able to muck around and make the process of stacking these images to create a timelapse into an action.
The process is straightforward: First run File>Automate>Load files into Stack. Select the files. Next my action selects the layers, converts to a Smart Object, then chooses Layers>Smart Objects>Stack Mode>Maximum, resulting in a star trail image.