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A few days ago, I took a photo of the night sky in the mountains of Georgia with my DSLR. There, I noticed that one single star (in the center of the part of the photo that I added below) looks very different than all the other stars on the photo. Why does it have this white glow?

enter image description here

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    $\begingroup$ There's some apparent motion blur as well. Can you post exposure time, did you use a tripod? Did you take more than one picture and the same light source remained "glowing"? It could even have been a small thin cloud or local turbulence cell, for that matter. $\endgroup$
    – Carl Witthoft
    Commented Feb 8, 2019 at 15:10
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    $\begingroup$ Given it's dead center of the image it could well be an optical effect - you get reflection effects of this sort from certain optical setups. These are particularly visible when the background is dark and the image contains (relatively) bright objects. $\endgroup$
    – StephenG - Help Ukraine
    Commented Feb 8, 2019 at 19:02
  • $\begingroup$ @CarlWitthoft 30s exposure. I used a small travel tripod placed on hard snow, so there might be some motion blur indeed. I took several photos, from slightly different positions and even with different lenses and on every single image, this light source is visible. $\endgroup$
    – Daniel
    Commented Feb 9, 2019 at 9:15
  • $\begingroup$ @StephenG It's in the centre of the screenshot that I posted above, but not in the centre of all the full-size photos. In some of them it's only 10% away from the top. $\endgroup$
    – Daniel
    Commented Feb 9, 2019 at 9:17
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    $\begingroup$ If you can add a full frame image, other items of interest can possibly be noted. Some contrast enhancement will help. It's a nice photo. $\endgroup$
    – Mick
    Commented Feb 9, 2019 at 12:43

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Astrometry.net has identified your star field as being part of the Andromeda constellation. The diffuse object in the centre of your image is the Andromeda Galaxy (Messier 31). The bright star to the left of it is Mirach (β Andromedae). Given a reasonably dark sky and averted vision, it is possible to see the core of M31 with the naked eye. Since M31 is approximately 2.5 million light years away from us, it is one of the most distant objects that can be seen with the naked eye.

Diametrically opposite Mirach to M31, and equidistant from it, is the Triangulum Galaxy (M33), although it is only just discernible in your photograph (even here, averted vision helps). If you can see M33 with your naked eye, then you have excellent vision and really dark skies. At a distance of 3 million light years, it is also one of the most distant objects that can be seen with the naked eye.

enter image description here

Astrometry.net

Note that only the core of M31 is visible to the naked eye (as it is in your photograph). If M31 was brighter, the arms of the galaxy would be visible and it would appear to be several times larger than the full Moon, as shown in the composite image below.

M31 and Moon composite photo

NASA

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