September 8, 2014: Super Harvest Moon
The bright Full Moon that lights up the sky tonight is known as the #Harvest Moon. Its name comes from the fact that it is the closest Full Moon to the autumnal equinox, which this year falls on Sept. 22. The Full Harvest Moon is expected to reach its full phase at 1:38 U.T. This year the Harvest Moon will also be a supermoon, the last one of the three summer supermoons (July, August, and now September).
A supermoon is the coincidence of a full moon or a new moon with the closest approach the Moon makes to the Earth on its elliptical orbit, resulting in the largest apparent size of the lunar disk as seen from Earth. The technical name is the perigee-syzygy of the Earth-Moon-Sun system. The term “super moon” is not astronomical, but originated in modern astrology - astrologer Richard Nolle coined it in 1979. Supermoon is not used within the astronomical community, which use the term perigee-syzygy or perigee full/new moon. Perigee is the point at which the Moon is closest in its orbit to the Earth, and syzygy is when the Earth, the Moon and the Sun are aligned, which happens at every full or new moon. Hence, a super moon can be regarded as a combination of the two, although they do not perfectly coincide each time. So, if you want to sound academic, use the scientific definition. If you’re more romantic, supermoon is just perfect.
The name “Harvest Moon” is attributed to Native Americans because it marked the period when corn was supposed to be harvested. At the peak of harvest, farmers can work late into the night by the light of this Moon. Usually the full Moon rises an average of 50 minutes later each night, but several nights in a row — before and after the full Moon — the Moon seems to rise at nearly the same: just 25 to 30 minutes later across the U.S., and only 10 to 20 minutes later for much of Canada and Europe. This has to do with the Moon’s path, which makes a narrow angle with the horizon at the beginning of autumn.
Both of these events give the illusion that the Harvest Moon is bigger, brighter, and closer, but it’s not. The Moon is simply closest to the horizon at sunset, when most people are looking for the Harvest Moon. When the Moon is near the horizon, it must pass through more dust and cloud particles that scatter blue light and only let red pass through. That’s why the Harvest Moon usually looks yellow, orange, or red.
In the Southern Hemisphere, because the autumn equinox falls in March, the Harvest Moon is the one happening closest it, in March or April.
Photo credit: Harvest moon over Little Belt Mountains by Scott Deck