Compare the size of the Moon on the horizon with its size higher in the sky. One way is to hold at arm's length various objects that will just barely block out the Moon.Experiment until you find something just right,perhaps a thick pencil or pen. You'll find that the object will be smaller than a centimeter, depending on the length of ypur arm. Is the Moon reallly bigger when it is near the horizon? Does it make sense what you see?

What is an optical illusion?