Harvest Moon

Tonight, September 20th, at 7:54 Eastern Time, the moon will reach peak illumination. You can observe the moon ascend soon after sunset in the southeastern sky.

The Harvest Moon is the full Moon in the Northern Hemisphere that occurs nearest to the fall equinox (two weeks before or two weeks after). This year the fall equinox takes place on September 23rd. Most years, this will happen in September, except every three years, it will occur in October. The timing depends on how the astronomical calendar correlates with the lunar cycle.

Why is this specific full Moon called the Harvest Moon? The name originated in European and Chinese cultures and with Native American and Colonial American peoples. Usually, the full moon rises around sunset and then 50 minutes later each day. However, near the autumnal equinox, it rises during twilight and only 20 to 25 minutes later daily (10 to 20 minutes later in latitudes farther north) for several days before and after the full Moon. This effect gave early farmers several additional dusk to dawn moonlit nights to permit them to finish their harvests before the killing fall frosts began.

How does this phenomenon happen?

But when does Fall begin? Another tricky question. Meteorological fall, based on the Gregorian calendar and temperature cycles, starts on September 1st. By the astronomical calendar, the first day of fall is the autumnal equinox in the Northern Hemisphere.

One final fascinating fact: the frequency of the aurora borealis, northern lights, peaks twice a year, in the weeks between the autumnal and vernal equinoxes. The lights occur during this time interval because this is also the time that geomagnetic storms are the strongest. Of course, you may need to travel to the Auroral Zone, a latitude of 66 to 69 degrees north (the northern regions of Alaska, Canada, Greenland, Scandinavia, and Russia), to enjoy the experience. PS Aurora Australias (southern lights) exist as well.