The Moon Illusion

Have you ever noticed that the moon sometimes appears absolutely gigantic when it's right near the horizon? You're not alone.
The moon illusion might be the world's most widely known optical illusion, and it's been pondered for thousands of years. There are actually records of ancient Babylonians and Greeks debating why the illusion occurs.
 We know the moon doesn't actually take up any more of the sky when it's near the horizon — it just looks that way to human eyes. But despite all the effort put toward understanding the illusion, we still don't really know why our brains perceive the moon as bigger when it's near the horizon.
 Recently, some neuroscientists have even begun using MRI studies to understand what's going on.