I mentioned an iPhone GPS app in my previous post. In that vein, I have another app to share: Star Walk.
This app is like something from a science fiction movie. Just hold it up to the sky, and the iPhone knows exactly where it is and gives an annotated view of the stars above. That's how I was able to see that my star trail photo was focused on Arcturus.
If you have an iPhone (or iPad), I highly recommend downloading this program.