This is the Hubble extreme deep field. With the exception of (from what I can find) 3 foreground stars, every object you see in this picture is a galaxy. Can you find the foreground stars? Know the trick?

@evilscientistca I don't know, but i would guess that the image has been colour adjusted for red shift, since stars are near they will have been shifted further into the blue part of the spectrum. So, look for the three bluest or indigo objects?

@StuC @evilscientistca

Red-/blue-shift refers to the Doppler shift in the absorption/emission lines in the spectrum, not the color of the objects. The color of stars (galaxy color is in large part due to the composite color of all contained stars) is largely due to temperature. Red stars are cooler while blue stars are hotter.

Robert Walker’s answer in this thread gives a thorough rundown of star colors in this thread:

@paanvaannd @StuC @evilscientistca My guess - Stars have diffraction effects from the secondary mirror spider assembly, due to being point sources of light compared to galaxies.

@vertigo @StuC @evilscientistca

I understand enough to know that it has to do with not being able to resolve point sources, which I know has to do with lens aperture diameter.

I would like to learn, though, so I would appreciate any extra information or resources!

Here's an r/AskScience thread on the image mentioning that diffraction spikes have to do with the telescope's point spread function (another thing for me to learn about):

@evilscientistca Diffraction spikes?

If so, I see two: one bright [¹] one just above centre in the bottom right quadrant and a still bright but somewhat fainter one about the same place in the top left quadrant.

[¹] Yeah, probably unimaginably faint by normal standards.

@evilscientistca And now it is (hopefully) only two years until the JWST launches!

@evilscientistca I don't know the trick, but I'm guessing they're the ones whose light forms a star-like glare... is it right? If so, why is it? 🙂

@thyago @evilscientistca

The diffraction spikes are because stars are too small to be resolved by the telescope.

/u/lmxbftw‘s answer in this thread is a good explanation of the phenomenon:

@evilscientistca [Terrible joke] Michael Bay put lens flare effect on stars, cuz they are from Hollywood!

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