Full moon
From Freepedia
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 the earth is fully illuminated by the sun at this time, presenting a "full" round disc to viewers on earth. As always, only half the total surface of the moon is illuminated.
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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 the earth. However, because of the tilt of the moon's orbit around the earth relative to the earth's orbit around the sun, the moon may pass above or below the shadow, 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 Formulas
Although it takes only 27.322 days (nearly exactly) for the moon to complete one orbit around the earth, it requires about 2 more days than that to again catch up with the sun. On average, the number of days between full moons is 29.5306 days. The actual number of days may differ from the average number by more than a half day, meaning that the number of days in one lunation can vary between a little less than 29 days and a little more than 30 days.
The age and apparent size of the full moon vary on cycle of just under 14 synodic months, which is called the full moon cycle.
The combinded date and time of full moon number N, using a fictitious moon that moves at a strictly average 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 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 will differ from this by more than 14 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 the earth, and nearby planets.
See the new moon page for a detailed explanation of the formula.
Folklore
Full moons are traditionally associated with insanity (hence the terms lunacy and lunatic) and with various magical phenomena such as lycanthropy.
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.
| 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. The Moon was used to track the seasons. (From Farmer's Almanac) | |||
Traditionally these names corresponded to the seasons rather than calendar months. So, for instance, the Egg Moon would always be the first moon after March 21st, and the Lentin Moon would always be the last moon on or before March 21st, the full moon before Easter.
The Blue Moon
- See the full article 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.
