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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.

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  • $\begingroup$ Are these pictures public or private? $\endgroup$
    – user21
    Jan 12, 2016 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, 2016 at 22:58
  • $\begingroup$ If you post them to reddit.com/r/Astronomy, the astro-bot should automatically annotate them $\endgroup$
    – user21
    Jan 12, 2016 at 23:26
  • $\begingroup$ I feel like I'm late to the party, but try lowering the shutter speed $\endgroup$
    – latetotheparty
    Nov 5, 2020 at 19:09

4 Answers 4

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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, 2014 at 5:33
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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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I think that the other approaches are a lot easier and faster, but here is another approach.

In case you know the approximate direction you pointed your camera, you can use planetarium software such as Stellarium to identify the stars:

  • Set your field of view to be equal to the photo you took (in Stellarium, you can specify sensor size and focal length)

  • Roughly align the view to your photo (this can often be done by memory; you can display constellation lines in any planetarium software too)

  • Take a screenshot of the program and overlay it to your photo in some laser-based photo editing software like Gimp or Photoshop.

  • Try to align both views by moving and rotating the screenshot. It might help to reduce brightness of your photo (which is basically the same as Aaron suggested)

  • You now have a detailed map of the stars in your photo

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I second nova.astrometry.net. For basic identification of constellations and brighter stars it's excellent and simple to use. Here's one of my images that includes part of Casseiopeia, identified by the website.

enter image description here

(source: https://flic.kr/p/2kKM4vA)

On the other hand, it has the drawback that the labeling is rather sparse. If you're looking to determine the faintest magnitude your DSLR can pick up with various lenses, that turns out to be more difficult. I try to do this by comparing my photos with astronomy apps like Sky Safari and Stellarium, but that approach likewise has its drawbacks.

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