How to Create Star Trails

For those of you who haven't seen my star trail picture on http://ruub.jalbum.net can check it out here. Because I didn't know if this would work with my cheap Samsung L73 compact camera I decided to only make a 150 second exposure. I obviously read how to do this in Practical Photography, issue November 2008. In Practical Photography they took 120 photos with an exposure of 30 seconds. The photos were of an interesting foreground object with a clear night sky in the background. I didn't have an interesting foreground object so I directed my camera at the night sky and started firing off shots, each with the longest exposure I could get, which is 15 seconds. If you want to make a star trail photo, here is how to do it:

1. Check the space on the memory card; you want to take a lot of pictures. I used 10 photos for the final image, and I wished I had taken 50 at least.
   
2. Put your camera on a tripod, directed at the sky. You don't have to direct it exactly at the polar star but it looked great in Practical Photography. I directed my camera NNE and it still turned out great.
   
3. Set your exposure to the longest possible. If you own a compact camera you might want to switch to Night Mode or something similar, to get the longest exposure.
   
4. If you can, set your camera in continuous shooting mode. Then you could use tape to keep the shutter button pressed down. Better still; buy a D-SLR and a cable release to go with it. That's what I'll do when I get richer. If you cannot put the camera in continuous shooting mode at least turn off the automatic preview function so there is as little delay between the pictures as possible.
   
5. Start taking pictures. My camera processor took a while to process each 15-second photo, which can be seen on the original photo as gaps between the stars' different positions.
   
6. After 5:48 minutes I decided it was cold and I wanted to see the result. If you want longer trails you'll have to stay out longer.
   

Now it's time to combine all these exposures so you get a nice looking trail:

1. Open up Paint.NET or GIMP.
   
2. Add all the images into layers. There is no specific order required.
   
3. Change the blending mode of all the layers to Lighten. In Paint.NET select each layer and press F4 and change the blending mode in the bottom of the properties box. In GIMP select each layer and change the blending mode in the layers dock (top right).
   
4. You should now have a star trail. If your camera needed some processing time between each photo, resulting in something resembling LEDs: continue reading.
   
5. Flatten your image (in both Paint.NET and GIMP go to Image>Flatten)
   
6. Select a group of star trails that have roughly the same angle (pointing in the same direction). In Paint.NET go to Effects>Blur>Motion Blur leave the effect to 10px and drag the angle in the circle so that it matches the angle of the selected star trails. In GIMP go to Filters>Blur>Motion Blur… adjust the angle by dragging the angle slider and keep an eye on the effect in the preview window.
   
7. Repeat the above step for all angles of star trails.
   

The effect is really cool and if you feel like it add a foreground object. Remember to "paint" some light onto the foreground object in the last photo (using a flashlight, flamethrower etc). Actually don't use a flamethrower or if you do don't blame me (but send me the pics).