Take some steel wool and press it into a metal food whisk. Attach the food whisk to a metal chain or cable and then ignite the steel wool. Spin this around and around whilst you take photographs. How? Set the camera on a tripod, iso 400 - 800. Shutter speed 2-3 second at F8-11 should do the trick, but if you want to capture more of the ambient light in the sky then leave the shutter open for at least two minutes. This are just a guide but when you are working with such long exposures an extra 20 second here and there doesn't make too much difference.