Medary.com

Space.com attempts to explain why the rising (or setting) full moon seems so much bigger than when it's up high in the sky:

The moon illusion, as it's known, is a trick in our minds that makes the moon seem bigger when it's near the horizon. The effect is most pronounced at full moon. Many people swear it's real, suggesting that perhaps Earth's atmosphere magnifies the moon.

It's going to happen tomorrow, Wednesday, June 18th.