Eli5: Why does the moon look different sizes depending on where/when you look?

Question

Eli5: Why does the moon look different sizes depending on where/when you look?

In: Earth Science

Answer 1

There is an optical illusion caused by surrounding objects.
When the moon is close to the horizon, next to it there are lots of buildings, trees, houses, etc.
When the moon is high up in the sky, there are no familiar objects next to it.

In order to help see 3D, the brain compares objects to the known size of nearby shapes. So we see the moon different sizes depending on surrounding objects.

To test this, you can make a hole in a cardboard, then see the moon through the small hole, the idea is to block all other objects with the cardboard.
Then rapidly remove the cardboard and compare sizes.