I captured image on a very dark night in Yellowstone National Park, just after I made the Milky Way image that I posted a few days ago. I like this image for a couple of reasons. First, it demonstrates just how many stars you can see on a clear dark night without light pollution. Nothing like shooting a hundred miles from the nearest town.1 Second, this is a great illustration that stars are many different colors. One can observe star colors with the naked eye, but this is a much more graphic way of seeing. Finally, I found it interesting that even the North Start (the center of the swirl of stars) moves ever so slightly. Be sure to click on the image for a better view of these details.
This is effectively a one-hour exposure. I say “effectively” because I made this image by combining approximately 120 30-second exposures. Digital camera sensors don’t react well to hour-long exposures: lots of noise, “hot” pixels, etc. Instead, the preferred technique is to make a series of short exposures, then merge them in post production. Capturing the images is easy. However, the tools to combine the images are still in their infancy. One of the standard image stacking programs, the “Startrails” application, doesn’t work very well. It generates star trails as dotted lines.2 I obtained much better results by using Chris and Dawn Schurs free Photoshop action. On a fast computer with lots of ram, it took me only about five minutes to stack ~120 images. However, setting up the action could be bit tricky if you’re not familiar with Photoshop.
- There are some downsides though: It is a bit nerve wracking to stand alone in a very dark place — one frequented by bears — waiting to complete the hour-long exposure. ↩
- The cause of this problem is beyond the scope of this entry. There is a very helpful article on NaturePhotographers.net that explains the phenomena and offers a complex solution. In defense of Startrails, it is both free and easy to use. ↩
