The Full Harvest Moon is the full moon that occurs closest to the autumnal equinox.
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All full moons rise around the time of sunset. Because the moon orbits the earth in the same direction the earth is rotating, the moon rises later each day – on average about 50 minutes later each day (24/29.5 hours, or the number of hours in a solar day divided by the number of solar days it takes for the moon to orbit the 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 much shorter than average. 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 for several days following the actual date of the full moon. 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 plane of moon's orbit around the earth makes a narrow angle with respect to the horizon in the evening in autumn.
The Harvest Moon is the full moon closest to the autumnal equinox. It is the first full moon closest to that equinox. About once every four years, it occurs in October in the northern hemisphere. Currently, the latest possible Harvest Moon is on October 11.
When the night of the Harvest Moon coincides with the night of the equinox, it is called a "Super Harvest Moon".[1] In 2010, the harvest moon happened only 5 1/2 hours after the autumnal equinox, creating the first Super Harvest Moon since 1991.[2]
Often, the Harvest Moon seems to be bigger or brighter or more colorful than other full moons. The warm color of the Moon shortly after it rises is caused by light from the Moon passing through a greater amount of atmospheric particles than when the moon is overhead. The atmosphere scatters the bluish component of moonlight which is really reflected white light from the sun, but allows the reddish component of the light to travel a straighter path to one's eyes. Hence all celestial bodies look reddish when they are low in the sky.
It appears larger in size because the brain perceives a low-hanging moon to be larger than one that's high in the sky. This is known as a Moon illusion, and it can be seen with any full Moon. It can also be seen with constellations; in other words, a constellation viewed low in the sky will appear bigger than when it is high in the sky.
The Harvest Moon is also known as the Wine Moon, the Singing Moon, "Blue Corn Moon", and the Elk Call Moon. In myth and folklore the full moon of each month is given a name. There are many variations.[3]
In some cultures, individuals whose birthdays fall on or near a harvest moon must provide a feast for the rest of the community.