Finding Satellites in Full Sky Photos

Recently I began a small project to photograph satellites in full sky images. The idea was using the same photographic techniques that you would use to create star trail photos it might be possible to mathematically remove the stars and only leave airplanes and satellites. I really want to see a clear photograph of how busy our night sky really is.

My first software version worked great, until my hard drive failed without having backed up that code. The loss of that code hurt but it gave me time to think up some improvements, and the next version was able to be recreated very quickly.

Last night I had some relatively fair weather so I thought I’d try to get about an hour and a half’s worth of full sky images. I decided on 20 second exposures to limit star trails, but also allow satellites to streak pretty far in each frame. The issue with this is that the more a satellite streaks, the less light it shines onto a specific pixel, meaning they show up as very dim.

Star trail photos are always fun to see, though obviously the camera thinks my trees are purple. There are a few things I noticed in this picture, there is an airplane that seems to skim above the north star, and a faint satellite that goes just to the right of the north star.

By using the software that I’ve been working on I was able to remove stars and leave only the streaks of airplanes and satellites.

I’m thrilled at how clearly this resulting photo came out! The airplane that went directly overhead is clearly seen, as is one in the bottom of the frame. The very dim satellite on the right side is much easier to pick out now as well. Some photo editing may be able to make the contrast on this a bit better too.

I’m a little upset that I wasn’t able to capture all the satellites that were scheduled to go overhead, but hopefully some camera settings tweaks can fix that. Once the software gets finalized I will post everything in a big package on this site.