Color-coded, time-lapse sky photo

Check out this fantastic time lapse photograph by Flickr user AnimalDetector. It was created by shooting a video, then processing the video into a color-coded still image.

The paths that the stars took over our yard last night. We filmed the night sky by long exposure timelapse. How do you do that, you ask? We used an inexpensive Canon point and shoot camera, hacked with open source CHDK software. Then, to make this picture, we used ImageJ software, also open source, to make a black and white film of only the moving objects by subtracting from each frame everything that was also on the previous frame. Then the film was time-coded with color, and all the colored frames were projected onto a single image. Color equals time in the final image: purple is just after sunset, and orange/yellow is later, almost sunrise. For example, the clouds appeared just before sunrise, and so they appear orange. The stars were going by all night long.

[Thanks, Bob!]