The Full Moon is the phase at which the Moon stands opposite the Sun in the sky, so that its entire near face is lit and the disc appears whole and bright. It rises around sunset and sets around sunrise, visible all night. The full moon fixes the timing of many festivals, Passover, Easter, and the mid-autumn and other observances across Asia are set by it, and it is the point at which a lunar eclipse can occur, when the Earth passes exactly between Sun and Moon. Traditionally the full moon is read as a time of culmination, fulfilment, and heightened intensity. These are the astronomical facts of the phase together with the meanings traditions attach to it; the full disc is simply the whole sunlit hemisphere of the Moon turned toward the Earth at opposition.
A full moon occurs roughly once every twenty-nine and a half days, but because that synodic period does not divide evenly into the solar year, most years contain twelve full moons while some contain thirteen, and when a second full moon falls within a single calendar month, a purely calendrical coincidence with no astronomical significance of its own, it has been called a blue moon in English usage since the twentieth century. In Wiccan and related modern pagan practice the full moon is marked by the Esbat, a monthly rite distinct from the eight solar Sabbats of the wheel of the year, and is traditionally associated with the Mother aspect of a threefold goddess figure, standing between the Maiden of the waxing crescent and the Crone of the waning phase in a scheme first popularised in the twentieth century rather than inherited from antiquity.
Sources AstronomyAndrew Fraknoi, David Morrison, and Sidney C. Wolff (OpenStax) with Wicca: A Guide for the Solitary PractitionerScott Cunningham, The Oxford Companion to the Year: An Exploration of Calendar Customs and Time-ReckoningBonnie Blackburn and Leofranc Holford-Strevens