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Full moon

A full moon is the lunar phase that occurs when the Moon is completely illuminated as seen from the Earth. This occurs when the moon is in opposition to the Sun (when it is on the opposite side of the Earth from the Sun; more precisely, when the ecliptic longitudes of the Sun and Moon differ by 180 degrees).[1] This means that the hemisphere of the Moon that is facing the Earth (the near side) is almost fully illuminated by the Sun and appears round (while the far side is almost completely unilluminated).

Lunar eclipses can occur only at full moon, where the Moon's orbit allows it to pass through the Earth's shadow. Lunar eclipses do not occur every month because the Moon usually passes above or below the Earth's shadow (which is mostly restricted to the ecliptic plane). Lunar eclipses can occur only when the full moon occurs near the two nodes of the orbit, either the ascending or descending node. This causes eclipses to only occur about every 6 months, and often 2 weeks before or after a solar eclipse at new moon at the opposite node.

The time interval between similar lunar phases—the synodic month—averages about 29.53 days. Therefore, in those lunar calendars in which each month begins on the new moon, the full moon falls on either the 14th or 15th of the lunar month. Because calendar months have a whole number of days, lunar months may be either 29 or 30 days long.

Full moon names[edit]

The full moon, as observed from Earth on a clear night.
Historically, month names are names of moons (lunations, not necessarily full moons) in lunisolar calendars. Since the introduction of the solar Julian calendar in the Roman Empire, and later the Gregorian calendar worldwide, month names have ceased to be perceived as "moon names". The traditional Old English month names were equated with the names of the Julian calendar from an early time (soon after Christianization, according to the testimony of Bede ca. AD 700).

Some full moons have developed new names in modern times, e.g., the blue moon, and the names "harvest moon" and "hunter's moon" for the full moons of autumn.

Harvest and hunter's moons[edit]

"Harvest moon" redirects here. For other uses, see Harvest moon (disambiguation).
"Hunter's moon" redirects here. For other uses, see Hunter's moon (disambiguation).

A harvest moon. Its orange color is due to its closeness to the horizon, rather than being unique to harvest moons.[7]
The "harvest moon" and "hunter's moon" are traditional terms for the full moons occurring during late summer and in the autumn, in the northern hemisphere usually in August, September and October respectively. The "harvest moon" is the full moon closest to the autumnal equinox (22 or 23 September), and the "hunter's moon" is the one following it. The names are recorded from the early 18th century.[8] OED for "harvest moon" cites a 1706 reference, and for "hunter's moon" a 1710 edition of The British Apollo, where the term is attributed to "the country people" (The Country People call this the Hunters-Moon.) The names became traditional in American folklore, where they are now often popularly attributed to the Native Americans.[9] The Feast of the Hunters' Moon is a yearly festival in Lafayette, Indiana, held in late September or early October each year since 1968.[10] In 2010, the Harvest moon occurred on the night of equinox itself (some 51⁄2 hours after the point of equinox) for the first time since 1991.[11][12]

Harvest_moonAll full moons rise around the time of sunset. Because the moon moves eastward among the stars faster than the sun its meridian passage is delayed, causing it to rise later each day – on average by about 50.47 minutes.[13] The harvest moon and hunter's moon are unique because the time difference between moonrises 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.

Farmers' Almanacs[edit]
The Maine Farmers' Almanac from c. the 1930s began to publish Native American "Indian" full moon names. The Farmers' Almanac (since 1955 published in Maine, but not the same publication as the Maine Farmers' Almanac) continues to do so.[14]

An early list of "Indian month names" was published in 1918 by Daniel Carter Beard in his The American Boy's Book of Signs, Signals and Symbols for use by the boy scouts. Beard's "Indian" month names were:[15]

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