See the Harvest Moon Wednesday, September 26, 2007

William Atkins
Friday, 21 September 2007 19:48

Science - Space

A Harvest Moon is a full Moon that appears closest to the autumnal equinox, which occurs in 2007 on September 23 in the northern hemisphere.            

The specific time in which the Moon is opposite the Sun, that of the Harvest Moon, for people in the northern hemisphere, occurs at 3:45 p.m. EDT on the eastern coast of the United States, 12:45 p.m. PDT on the western coast, which is also 1945 Greenwich Time (GMT), on September 26, 2007.

The name “Harvest Moon” is named so because farmers are able to work later at night “harvesting” their crops due to the reflected light coming off of the full Moon. Specifically during this time, the Moon rises into the sky just after the Sun sets and, most importantly, there is full moonlight almost from sunset to sunrise because the Moon is at its minimum with respect to retardation (its rising later after sunset on successive nights).

In other words, at other times during the year the Moon rises about 50 minutes later each successive night as it moves in its orbit about the Earth. However, around the time of a Harvest Moon, the Moon rises about 30 minutes later from one night to the next due to its path around the Earth and the path of the Earth about the Sun. Consequently, this situation provides almost continuous light to work by for farmers in their fields and for other people just enjoying being outside during this time.

An autumnal equinox, like a spring equinox, is an astronomical event that occurs on the Earth when the Sun is located at the intersection point with celestial equator and the ecliptic (the plane of the Earth’s orbit around the Sun). The autumnal equinox occurs specifically at 5:51 EDT (2:51 PDT), which is also 9:51 Coordinated Universal Time (UTC), on September 23. At that point the Sun is directly above the Earth’s equator, and the amount of daylight hours and nighttime hours are approximately of the same length.