Full moon

2007 Schools Wikipedia Selection. Related subjects: Space (Astronomy)

The Galileo spacecraft took this composite image on 7 December 1992 on its way to explore the Jupiter system in 1995-97. The colour is 'enhanced' in the sense that the CCD camera is sensitive to near infrared wavelengths of light beyond human vision.

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 × N ²

• D is the number of days (and fractions) since 1 January 2000 00:00:00 UTC,
• N is a count of Full Moons, starting with zero for the first Full Moon that falls in the year 2000.

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

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

Folklore

Southeast Asian and Western folklore long ago established the Full Moon as the time for werewolves and vampires to awaken, or appear most often. As suggested in the film Wolf (1994; Jack Nicholson, Michelle Pfeiffer, James Spader; Directed by Mike Nichols) the creators of these myths explained away violence occurring during the middle of each month, when in fact the moon simply adds more light to the evening sky. This allows criminals to act more freely. It also helped assuage the guilt of the masses for not doing more to stop violent crime, and freed people to vilify brutality, while fantasizing and apologizing for it.

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.

Many neopagans hold a monthly ritual called an Esbat at each Full Moon, while some people practicing traditional Chinese religions prepare their ritual offerings to their ancestors and deities on every Full Moon and New Moon.

Calendars

The Hindu Calendars, Hebrew calendar, Islamic calendar, Tibetan calendar Neopagan calendar, Celtic calendar, and the traditional Chinese calendar are all based on the phases of the Moon. None of these calendars, however, begin their months with the Full Moon.

In the Chinese calendar, Jewish Calendar and some Hindu calendars, 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.

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.