Hi Alex
I thought that too until I read a few web pages on how to do it.
Startrails is free and you can also make avi. movies as well.
Heres a link to one of the many sites on how to capture these.
http://earthsky.org/astronomy-essent...re-star-trails
Also startrails
http://www.startrails.de/html/software.html
Can't wait to try one for more than a couple of hours rather than 25 minutes like this one.
Cheers
Andy