June 20, 2005: Sometimes you can't believe your eyes. This week is one of those times.
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.
Sky watchers have known this for thousands of years: moons hanging low in the sky look unnaturally big. Cameras don't see it, but our eyes do. It's a real illusion. This week's full moon hangs lower in the sky than any full moon since June 1987, so the Moon Illusion is going to be extra strong.
What makes the moon so low? It's summer. Remember, the sun and the full Moon are on opposite sides of the sky. During summer the sun is high, which means the full moon must be low. This weeks full moon occurs on June 22nd, barely a day after the summer solstice on June 21st--perfect timing for the Moon Illusion.