Soo I stumbled across an article with a photo of star trails.
It looks pretty cool so I have been trying to figure out how to do something similar.
I started out with long exposures but with long exposures of several minutes the chance of getting grain unwanted movement and that sort of stuff is far greater than the chance of it turning out the way you want it.
Sooo to get it I figured that I could do multiple shorter exposures and then merge them aftewards. The only issue with this is that you can get some pretty big files and alot of them. This makes the merging slightly difficult and demanding resources your computer may not have. Imagine the task of opening 200 5Mb files. This will take up your memory and use a lot of disk swapping making it painfully slow.
However I found photoshop action that will open one photo at the time and merge it with another ending with several photos being merged into one photo without killing the computer in the process and best of all --- it's automatic.
I did the first test but about 10 minutes into it the clouds came in.... sooo so much for that idea. However I did get about 50 shots without clouds and the result is here:
The photoshop action I used can be found here: http://www.schursastrophotography.com/software/photoshop/startrails.html
Now since I had about 150 photos in total I found another thing to do with them. I was browsing through them and could see the movement of the stars and the clouds coming in. Soo I set off to create an animation for this.
I "just" needed to find the right tool for it.... Easier said than done...
Anyway for now I ended up with a trial version of Adobe flash which you can use free for 30 days.
Then of course I had to learn how to as easy as possible load up 150 photos and "spit" out an animation.
To help with this I found a small video that did the trick. You can find that here: http://www.learnflash.com/creating-slideshows.html
You can see the animation here: Stars in action
All shots was done as 15 second exposure at f/2.0. I started out with the time period I figured would give the best image and the optimized the aperture after that.