We've all seen this: At moonrise on the day of the full moon, the moon is huge! Later that evening, however, it seems to have shrunk by at least half. Later still, when it's right overhead, it looks positively tiny.

It's all an optical illusion: The Moon Illusion.

The moon is the same size regardless of how low or high it is above the horizon. To prove this to yourself, cut out a circle just big enough to block the moon at arm's length and use it to see for yourself that its size stays the same as it rises in the sky.