at the australian astronomical observatory, i work with the people behind a project called GAMA: Galaxy And Mass Assembly. my recent trips to the observatory have been to help the team collect data for the project and determine redshifts for the galaxies observed each night.
one particularly cloudy night (at least in the direction where our targets were located), we decided to have some photographic fun with long exposure images! what you see is the dome of the AAT telescope we use, GAMA, a capital greek letter "gama" in green, and the milky way galaxy with the southern cross to the left of the dome (can you spot it?)...
how did we do it?
we sat a digital camera on a tripod on the ground and opened the shutter for about 4 minutes. usually when you take a photo, the shutter opens for roughly a second and then closes again.... viola, a photo! but, you can usually set the shutter to stay open for a little longer if you want, if the target is faint and you want to collect more light, or shorter, if the target is particularly bright and you dont want to saturate the image. the trick is that you need the camera to remain very stable during the longer exposure or else the lights will form wiggly trails.
we had a slightly fancier-than-average digital camera that allowed us to expose for 4 minutes (and by "we" i mean el lobo rayato ;). there was one person up on the dome's catwalk who slowly spelled out "GAMA" (backwards) with his flashlight/torch during the exposure. meanwhile, i was standing next to the camera with my green laser pointer and i made a very quick shape of the capital greek letter gama on the side of the dome below. the rest of the 4 minutes we kept all our lights off so that the stars would come through. near the end of the 4 minute exposure, a flashlight/torch was passed over the whole dome in strips to illuminate it a bit in the shot... or else it would have been completely dark. the result came out really nice, i think!
here's another example of a long exposure photograph. this one was 15 minutes and shows the trails of the stars as they rotate around the southern celestial pole.