For some of you this might be an old topic, but I just discovered this a few days ago. I've run into it by accident while searching for something else. It details a different way of taking a photo of star trails. Basically instead of leaving the camera's shutter open for a long time, like 40 min or longer, one takes multiple photos of 4 to 5 minutes exposure time. The whole reason for this is that with digital sensors opening a shutter for long periods of time will introduce digital noise in the picture. Keeping the exposures shorter minimizes that noise. I was very eager to try this, and last night was a perfect clear evening. So I setup my tripod on the deck and started snapping away. Of course a remote cord is handy so you don't have to touch the camera, and keep it still. I took 19 images of 4min each at 100 ISO and f5.6. Then taken the images into Adobe Photoshop and each image at a separate layer. This is what I got.

Next task is to find a better location.