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General Interest > Science and Technology
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Why do stars appear as large as galaxies in space pics?
    #12398406 -

I'll get right to the point here.  This is a question that I've been meaning to find an answer to for a while.  I enjoy looking at pics from Hubble and other telescopes, but one thing always stood out that didn't make sense.  In shots of an entire galaxy, there are countless stars all around the galaxy that appear to be entirely too large in ratio compared to a galaxy.

The galaxy of course will have millions if not billions of stars in it, and yet some of the bright shining points of light around the galaxy are also stars I assume?  Why do they appear so big in contrast to the galaxy?  Is it because they are actually much closer to the lens of the telescope compared to the galaxy, therefore making them look extremely large in the photos?

The pic below is a prime example.  A galaxy in the middle with billions of stars in it, and yet if you look all around that picture you'll see blue and orange stars that appear huge.  What exactly is going on here?



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:super:D
Manoa said:
I need to stop spending all my money on plants and take up a cheaper hobby, like heroin. :lol:

Looking for Rauhocereus riosaniensis seeds or live specimen(s), :pm: me if you have any for trade

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Re: Why do stars appear as large as galaxies in space pics? [Re: SuperD]
    #12398414 -

Camera Flare.


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l'enfer c'est les autres

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Re: Why do stars appear as large as galaxies in space pics? [Re: VisionaryFlicker]
    #12398580 -

The stars you see are the stars in our galaxy, so they are closer to you than the galaxy

Just as likely, some of those 'stars' could be galaxies, even further away


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uk grow logs

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Re: Why do stars appear as large as galaxies in space pics? [Re: Frinkz]
    #12398611 -

The blue and orange stars are just a lot brighter than others, making them appear bigger in the picture. They are either nearby and therefore bright, or far away but large/bright/galaxies.

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Re: Why do stars appear as large as galaxies in space pics? [Re: koraks]
    #12399018 -

Thanks for the responses.  All of those seem like logical explanations. :cheers:


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:super:D
Manoa said:
I need to stop spending all my money on plants and take up a cheaper hobby, like heroin. :lol:

Looking for Rauhocereus riosaniensis seeds or live specimen(s), :pm: me if you have any for trade

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Re: Why do stars appear as large as galaxies in space pics? [Re: SuperD]
    #12400232 -

More light from those stars hits the telescope because it is much closer to the telescope than the galaxies. Although the light from a star would ideally only be a single pixel, at least with current detector (CCD) resolutions, telescopes are at best limited by diffraction.
A point source appears as an Airy disk on the telescope's detector:



The size of the Airy disk becomes smaller with larger telescope aperture.
That's why better telescopes produce smaller stars; the Airy disk is smaller (in width).

When a light source is dimmer, you only see the top of the Airy disk, that's why the Airy disk appears smaller when a star is further away from the telescope. We don't yet actually see the size of the star itself, it's just a point source producing an Airy disk due to diffraction.

There are also many other lens/mirror and detector artefacts that cause these kind of effects. (edit:) And atmospheric interference for ground based telescopes.  However, the diffraction limit is a physical limit and can only be decreased by a larger aperture.

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Re: Why do stars appear as large as galaxies in space pics? [Re: Annom]
    #12400742 -

Awesome explanation, thank you.


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:super:D
Manoa said:
I need to stop spending all my money on plants and take up a cheaper hobby, like heroin. :lol:

Looking for Rauhocereus riosaniensis seeds or live specimen(s), :pm: me if you have any for trade

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Re: Why do stars appear as large as galaxies in space pics? [Re: SuperD]
    #12401904 -

Yes, good explanation, Annom. That nails it.

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