Full moon

related topics
{math, energy, light}
{day, year, event}
{god, call, give}
{language, word, form}
{disease, patient, cell}
{country, population, people}
{church, century, christian}

Full moon is a lunar phase that occurs when the Moon is on the opposite side of the Earth from the Sun. More precisely, a full moon occurs when the geocentric apparent (ecliptic) longitudes of the Sun and Moon differ by 180 degrees; the Moon is then in opposition with the Sun.[1] As seen from Earth, the hemisphere of the Moon that is facing the earth (the near side) is almost fully illuminated by the Sun and appears round. Only during a full moon is the opposite hemisphere of the Moon, which is not visible from Earth (the far side), completely unilluminated.

The time interval between similar lunar phases—the synodic month—is on average 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 lunar months have a whole number of days, lunar months may be either 29 or 30 days long.



A full moon is often thought of as an event of a full night's duration. This is somewhat misleading, as the Moon seen from Earth is continuously becoming larger or smaller (though much too slowly to notice with the naked eye). Its absolute maximum size occurs at the moment expansion has stopped, and when graphed, its tangent slope is zero. For any given location, about half of these absolute maximum full moons will be potentially visible, as the other half occur during the day, when the full moon is below the horizon. Many almanacs list full moons not just by date, but by their exact time as well, usually in Coordinated Universal Time (UTC)). Typical monthly calendars that include phases of the moon may be off by one day if intended for use in a different time zone.

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.

On 12 December 2008 the full moon occurred closer to the Earth than it has done at any time for the past 15 years.[2]


The date and approximate time of a specific full moon (assuming a circular orbit) can be calculated from the following equation:[3]

Full article ▸

related documents
Tropical year
Saros cycle
Time standard
Eclipse cycle
Sidereal time
Time zone
SN 1987A
Angular displacement
Orbital period
Yarkovsky effect
Johnson solid
Mercator projection
Atomic nucleus
Carlo Rubbia
Exotic atom
Radio astronomy
Kristian Birkeland
Large Magellanic Cloud
Longitudinal wave
Spherical coordinate system
Wien's displacement law
Celestial pole
Confocal laser scanning microscopy
Red giant
Wave plate