I can look at a star chart and identify things like constellations in the sky. But if I take a picture with my DSLR camera (35mm with a decent zoom lens, no astronomy specific optics), I run into difficulty. I find that the camera can see a lot more stars than my eye, and I find that I start to have great difficulty even identifying simply constellations. For instance, when I look for the constellation Cassiopeia in the night sky it is very easy to spot: it looks like a sideways "W". But when I take a picture I don't see a W at all in the picture, I see about 16 stars around where the "W" should be a weird angles to each other, and it's hard to figure out which stars to connect to form the actual constellation.

And it just goes downhill from there, as other constellations don't even have a shape as easily recognizable as Cassiopeia, and as a result I have a great deal of difficult even recognizing what I am looking at.

A photograph with a regular camera is not quite the same as looking through a telescope, because the camera has a much wider field of view. And at the same time, there does not seem to be a linear relationship between the actual magnitude of the star and how bright it looks. As I mentioned above, I see 16 stars which look somewhat comparable in brightness, but I know that they differ by several magnitudes.

Is there some kind of trick or technique that I can use to quickly identify stars in pictures I take? In looking for clues, I have not seen anybody mentioning this problem.

  • $\begingroup$ Are these pictures public or private? $\endgroup$ – user21 Jan 12 '16 at 22:27
  • $\begingroup$ @barrycarter Well, at the moment they are just sitting somewhere on my hard drive, so I suppose that makes them private. However, aside from their location there isn't anything particularly private about them. $\endgroup$ – Michael Jan 12 '16 at 22:58
  • $\begingroup$ If you post them to reddit.com/r/Astronomy, the astro-bot should automatically annotate them $\endgroup$ – user21 Jan 12 '16 at 23:26

Take another photograph of the same field that is less exposed. (Doesn't matter if you do this by shortening the exposure time, decreasing the ISO, etc.) This will give you an image with far fewer stars so you can easily pattern match your images.

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    $\begingroup$ Complementary to this great answer, I'd like to point to Astrometry. You can upload your photo there and it will try to identify the stars on the picture. In my experience it works great. Lots of output options, like export to FITS format. $\endgroup$ – agtoever Sep 3 '14 at 5:33

This is basically @agtoever comment, converted to an answer as a community wiki.

There is an online service http://nova.astrometry.net/ which can identify star fields in photographs, and so convert from pixel position to ra/dec. It can export to FITS and generally seems to work well.

Also, a bot on reddit.com/r/Astronomy can automatically annotate them images posted there, if you don't mind others seeing them.

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