Source: http://gizmodo.com/5954460/why-the-moon-looks-bigger-on-some-nights-than-it-does-on-others
The moon looks HUGE some nights, right? Well, yes, sort of, to you—but only because your tiny human brain contextualizes it as larger sometimes than others. It's never actually any closer. It's just a confluence of a few different optical illusions screwing with your head.
So here's what happens. First, the moon seems larger, usually, when it's near the horizon. One reason for the is that there are more reference points, like trees and buildings, to compare to the moon. When it's just sitting alone, high in the night sky, the moon just looks "regular" sized. It's the Ebbinghaus effect—you look taller standing next to a child than you would standing next to Shaq. The other thing is that our brains are used to things on the horizon shrinking, since that typically means they're farther away. So when the moon doesn't shrink as it crosses the horizon, years of understanding perspective kicks in and tells us the moon got humongous. So there you go. Your brain is dumb, and the moon is just the moon. [YouTube]