Essentially, your brain is slightly faster at interpreting bright optical signals compared to dim ones, and as a result whenever you move either your eyes or the screen there is a split second delay in apparent movement of the bright moon and much dimmer background.
So to your eye, the moon appears to move ever so slightly faster than the background, and this gives the image an appearance of depth. Much like when you're in a car and objects right next to the road seem to move faster than the ones on the horizon.
Tom Scott has an excellent video (3:30 min) on the subject if you happen to have sunglasses nearby, which gives pretty clear demonstration of just how strong this effect can be.
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u/SalamandarShell Dec 13 '19
This is so ridiculously clear it somehow appears 3D.