Thanks John!
Its actually not a continuous 30min exposure. ; Unlike star trails on film (which had its own problems) digital sensors can't handle exposures of that length without overheating and creating extra noise. ; So, the solution is to create a series of many shorter exposures and then stack them. ; I didn't bring the intevelometer remote with me on that trip, so after taking a correctly exposed shot of the temple, I set the camera for a 30s exposure and locked the remote button so it fired continuously.
Stacking them is easy. ; There's a free program called Startrails that will automatically stack the shots for you if you're working with JPEGs. ; I was working with the raw files to bring out some of the shadows in the temple, so I ended up stacking them by hand in Photoshop. ; I placed all of the star trail shots on individual layers and changed the layer blending from "normal" to "lighten". ; Next I added the temple shot to the top of the stack and masked out the sky to allow the stars to show through without allowing the overexposed temple to show through.
