The Harvest Moon is the full Moon closest to the autumnal equinox (hello, Southern Hemisphere, you get yours six months from now). This year it happens only six hours away from the moment of equinox itself, and some are therefore referring to it as the Harvestest Moon.

Get outside at sunset on September 22nd, 23rd, or 24th and you'll see the Harvest Moon rising in the east. Check out the illusion for yourself -- does it look big when it's near the horizon? What if you bend over and look at it upside-down between your knees? What if you wait a few hours until it's higher in the sky?