"Step outside any evening at sunset and look around. You'll see a giant moon rising in the east. It looks like Earth's moon, round and cratered; the Man in the Moon is in his usual place. But something's wrong. This full moon is strangely inflated. It's huge! You've just experienced the Moon Illusion."

The moon illusion has been studied by astronomers, psychologists, and brain researchers. Scientists have written sophisticated research papers and even entire books about the moon illusion, but still a complete and satisfying solution seems out of reach. The problem is so simple and yet so profound. Anyone could devise a new experiment to try and resolve the mystery. Perhaps you, your friends, or your family can discover the crucial piece of evidence that allows us to understand exactly why the moon appears larger near the horizon.

"Look how big the moon is!" you've shouted before. But what if I told you that the moon never really changes size, and it's simply your brain playing a trick? Find out what The Moon Illusion is, and why it happens!

It's almost certain you have seen this yourself: The Full Moon rises over the horizon, bloated and fat. But a few hours later it is high in the sky and appears much smaller. Why? Phil Plait's Bad Astronomy answers.