Full moon

The Full Moon is the lunar phase that occurs when the Moon lies on the opposite side of Earth from the Sun. The Moon as seen from the surface of Earth is fully illuminated by the Sun at this time, presenting a "full" round disk to viewers on Earth. As always, only half the total surface of the Moon is illuminated.

Eclipses

A Full Moon is the only time when a lunar eclipse is possible; at that time the Moon may move through the shadow cast by Earth. However, because of the tilt or inclination of the Moon's orbit around Earth relative to Earth's orbit around the Sun, the Moon usually passes to the north or south of Earth's shadow at Full Moon, so a lunar eclipse does not occur at every Full Moon.

Full Moons are generally a poor time to conduct astronomical observations, since the bright reflected sunlight from the Moon overwhelms the dimmer light from stars.

Numbers and formulae

Although on average it takes only 27.322 days (sidereal month) for the Moon to complete one orbit around Earth, it requires about two more days than that to again catch up with the Sun. On average, the number of days between Full Moons is about 29.5306 days. The actual number of days may differ from the average number by more than a half day. From one Full Moon to the next, the number of days in one lunation can vary between 29.272 and 29.833 days.

The age and apparent size of the Full Moon vary in a cycle of just under 14 synodic months, which is called the Full moon cycle.

The combined date and time of Full Moon number N, using a fictitious moon that moves at a strictly mean rate is approximately:

D = 20.362954 + 29.5305888531 × N + 102.19 × 10^-12 × N²

D is the number of days (and fractions) since 1 January 2000 00:00:00 UTC,
N is the count of full moons starting with zero as the first (not 1 as you would have expected) as the first Moon in the year 2000.

The true Full Moon may differ from this by up to about 14.5 hours, due to the normal irregularity in the Moon's Keplerian orbit, and due to the periodic perturbations on that Keplerian orbit by the Sun, the equatorial bulge of Earth, and nearby planets.

See the New Moon page for a detailed explanation of the formula.

Folklore

Full Moons are traditionally associated with temporal insomnia, insanity (hence the terms lunacy and lunatic) and various magical phenomena such as lycanthropy.

Psychologists have found that there is no strong evidence for effects on behaviour around Full Moon . They find that studies are not consistent, with some showing a positive effect, while others will show a negative effect. In one instance, the December 23, 2000 issue of the British Medical Journal published two studies on dog bite admission to hospitals in England and Australia. The study of the Bradford Royal Infirmary found that dog bites were twice as common at Full Moon, while the study of public hospitals in Australia found they were less likely at Full Moon. Psychologists point out that there is a difference between correlation and causation. The mere fact that two events happen at the same time doesn't mean that there is a cause and effect relationship between the two.

Neopagans hold a monthly ritual called an Esbat at each Full Moon.

Many people practicing traditional Chinese religions prepare their ritual offerings to their ancestors and deities on every Full Moon and New Moon.

Calendars

The Islamic calendar and the traditional Chinese calendar are both based on the phases of the Moon. Neither calendar, however, begins its months with the Full Moon.

In the Chinese calendar, the Full Moon is always the middle of a month. The Mid-Autumn Festival falls on the Full Moon of the eighth month. The Lantern Festival falls on the first Full Moon of the year.

Full Moon names

Folklore assigns a special name to each Full Moon, although the rule for determining which name will be assigned to which Moon has changed over time (see article at blue moon).

Modern practice is to assign the traditional names based on the Gregorian calendar month in which the Full Moon falls. This frequently results in the same name as the older method would, and is far more convenient in practice. The older method of assigning names is based on seasons and quarters of the year.

**Full Moon Names**
Month	English Names	Native American Names	Other Names Used
January	Moon After Yule	Wolf Moon	Old Moon
February	Wolf Moon	Snow Moon	Hunger Moon
March	Lenten Moon	Worm Moon	Crow Moon, Crust Moon, Sugar Moon, Sap Moon
April	Egg Moon	Pink Moon	Sprouting Grass Moon, Fish Moon
May	Milk Moon	Flower Moon	Corn Planting Moon
June	Flower Moon	Strawberry Moon	Rose Moon, Hot Moon
July	Hay Moon	Buck Moon	Thunder Moon
August	Grain Moon	Sturgeon Moon	Red Moon, Green Corn Moon
September	Fruit Moon	Harvest Moon	Corn Moon, Barley Moon
October	Harvest Moon	Hunter's Moon	Travel Moon, Dying Grass Moon
November	Hunter's Moon	Beaver Moon	Frost Moon
December	Moon Before Yule	Cold Moon	Long Nights Moon
These are the traditional English names for each month's Full Moon and the names given by Native Americans in the northern and eastern United States. "Full Moon Names and Their Meanings - from the Farmer's Almanac. URL accessed March 16, 2006.

Traditionally these names corresponded to the seasons rather than calendar months. So, for instance, the Egg Moon (the Full Moon before Easter) would always be the first moon after March 21st, and the Lenten Moon would always be the last moon on or before March 21st.

The Blue moon

The origin of the folkloric term "Blue Moon" is complicated, because its meaning has changed over time. Modern practice is to name a Full Moon a blue moon if it is the second of two Full Moons to occur in the same calendar month. The original meaning of blue moon was the third Full Moon in a season when there were four Full Moons in that season.

References

Moon

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