The stars make arcs in the sky in long exposures. This image was composed from about 120 individual wide-angle photos taken with a Nikon D7000 on a tripod.
When people used film cameras (some of us still do!) it was a very easy thing to set up a camera on a tripod and let the stars wheel overhead, tracing enchanting arcs across the sky. There is an even better way to do it today, with digital cameras.
Digital cameras don’t like being on too long, because their sensors heat up and start producing noise. Some clever people have created a work-around, called stacking. In stacking, you take many short exposures and then process them together to make a combined longer exposure image.
A nice free software package called StarStaX is available to do the computing for you:
http://www.markus-enzweiler.de/software/software.html
It comes with examples and tutorial information. Give it a try!
An advantage of this approach to making star trail images is that the software can apply different methods (or algorithms) for combining each individual frame into the stack: it d
Pine River Observ-atory 