There are a couple of ways:


1. As mentioned, a cable release and a boatload of battery juice. A trail will start forming based on thefocal length. A longer focal length will show trails faster than a wide. Generally, the longer the exposuer thelonger and brighter thetrails.


2. Stack images. This is my preferred method.Instead of a single 45 min long expouser, take a series of smaller expousers of the same length and f stop (say2' at F8)and stackthem using Image Stacker or photoshop. If you have an interesting fore ground element, take a singlelonger exposuer, say 5' versus 2and blend that frame into the stack.


Makesure you have something interesting in the foreground. An egg timer helps with timing of expousers. Bring a book, caffinee, and warm clothes. In the northern hemisphere, the sky is better for starts in the dead of winter and not the height of summer. Having the NorthStar will cause full circles of trail and then arcs depending on how far the NS is away from the image.