Monday, September 12, 2011
All full moons rise around the time of sunset. In general the moon rises about 50 minutes later each day. As it moves in orbit around Earth, the Harvest Moon and Hunter's Moon are special because, around the time of these full moons, the time difference between moonrise on successive evenings is shorter than usual. This means that the moon rises approximately 30 minutes later from one night to the next, as seen from about 40 degrees N. or S. latitude. Thus, there is no long period of darkness between sunset and moonrise around the time following these full moons. In times past this feature of these autumn moons was said to help farmers working to bring in their crops (or, in the case of the Hunter's Moon, hunters tracking their prey). They could continue being productive by moonlight even after the sun had set. Hence the name Harvest Moon.The reason for the shorter-than-usual rising time between successive moonrises around the time of the Harvest and Hunter's Moon is that the ecliptic—the plane of Earth's orbit around the sun—makes a narrow angle with respect to the horizon in the evening in autumn.