I had seen this technique in many pictures on the internet and in different magazines, so I thought I would try it out myself. Basically, if you have a tripod and your camera has a bulb setting, you can create these cool looking shots with an exposure of about 15-20 mins, or longer depending on the effect you would like. If you would like the stars to seem to rotate about a certain point, like my shot, then you will have to include Polaris, the North Star, somewhere in your shot. For people south of the equator, I'm not sure which star is the southern celestial pole, but you would have to include that one depending on your location. Northerners, find the last star in the handle of the little dipper and you're good to go. Position the star in your frame, add maybe a tree like I did for some foreground, and make sure you don't bumb the camera or cuase any vibrations during the exposure. If you don't have a remote or cable release for your bulb setting (like me), you can set your camera to its highest exposure length (mine is 30 sec), and take multiple shots, one after another. Try to leave as little time between shots as possible in order to avoid gaps in your trails. Once you have taken about 20-30 exposures, you must stack them on top of one another. I used a program called RegiStax found at
http://registax.astronomy.net to stack my exposures on top of one another. The result is a cool looking star trail behind a tree in my backyard!
Settings:
28mm @ f/3.3
400 ISO
White balance: Incandescent
30 sec x 37 exposures
Stacked with RegiStax
Note: I realize my trails are not as bright as other pictures. I haven't had time to do it again and bump the ISO to 800 or even 1600, but this would obviously create much brighter stars (and more noise). If anyone else has experience with trails, let me know how you fared with your own settings, etc. Thanks!