The Harvest Moon is no ordinary full moon; it behaves in a special way. Throughout the year the Moon rises, on average, about 50 minutes later each day. But near the autumnal equinox, which comes this year on Sept. 22nd, the day-to-day difference in the local time of moonrise is only 30 minutes. The Moon will rise around sunset tonight--and not long after sunset for the next few evenings.

That comes in handy for northern farmers who are working long days to harvest their crops before autumn. The extra dose of lighting afforded by the full Moon closest to the equinox is what gives the Harvest Moon its name. In the southern hemisphere, this week's full Moon behaves in exactly the opposite way: there will be an extra long time between moonrises from one evening to the next.