ELI5: Why does the moon sometimes appear so much larger when it is near the horizon?

The Moon looks much bigger near the horizon because of an optical illusion where your brain tricks you into thinking it is larger than it really is.

The Moon never actually changes its size, and it stays the exact same distance away from Earth all night long. What changes is the way your brain sees the world around it.

Here is how your brain plays this trick on you:

• The comparison trick: When the Moon is high up in the middle of the empty sky, it sits all by itself with nothing nearby to compare it to. But when the Moon is low down near the horizon, you see it next to familiar things like trees, houses, and distant mountains. Your brain knows that houses and trees are big, so when it sees the Moon sitting right behind them, it assumes the Moon must be gigantic.
• The flat sky trick: Your brain thinks the sky is shaped like an upside-down cereal bowl rather than a round dome. Because of this, your brain believes that the horizon is much further away from you than the sky straight above your head. When your brain sees the Moon at that "super far away" horizon, it automatically magnifies the image to make sense of it.

• Roll up a piece of paper into a small tube, like a telescope.
• Look at the giant horizon Moon through the tube so that all the trees and buildings are hidden from view.
• Instantly, the Moon will look like its normal, smaller self again because you blocked out all the objects your brain was using to make the comparison.