Why the sun is bigger at sunrise?

When it goes dark tonight have a look at the setting sun and rising moon. You may notice that they look bigger than when they are high in the sky. But it’s just an optical illusion, that is caused be various reason:

When the sun rises and sets, there are things like mountains, trees and buildings beside it that make it seem very huge. When the sun is high above us in the sky there is nothing that can be used to compare its size with the sun, so we feel it is smaller.

The other part has to deal with the thickness of the atmosphere at the horizon than directly above us. The atmosphere can have a slight magnifying affect.

The perception and your ability to look at the sun longer means you can optically define it as a “size” than when you look at it as a blinding glaring dot in the sky over head. All three factors add up to make the sun appear larger than it actually is.