Waning Gibbous

The Waning Gibbous is the phase following the full moon, when the disc, still more than half lit, begins to diminish night by night, the illumination decreasing from full toward half. The waning gibbous Moon rises after sunset, later each night, and is best seen in the late night and early morning. Traditionally it is read as a phase of gratitude, sharing, and dissemination, the giving out of what the full moon brought to ripeness, and it opens the waning half of the cycle associated with release. These are the astronomical facts of the phase together with the meanings traditions attach to it; the shape is simply the sunlit hemisphere of the Moon seen from an angle that now reveals a shrinking portion as the Moon moves on past opposition toward the Sun.

The waning gibbous Moon is also called the disseminating Moon in some modern astrological and Wiccan sources, a name that frames it explicitly as the phase of spreading outward what the full moon brought to completion, in contrast to the waxing gibbous, which is read as gathering inward toward that same peak. Astronomically the phase is the mirror of the waxing gibbous in illumination but not in timing, since it rises later each night after the full moon rather than earlier, a practical distinction that determined, in pre-electric societies, whether a traveller could expect useful moonlight in the early evening or only well past midnight. The shift from convenient early light to inconvenient late light across the turn from waxing to waning gibbous was, before artificial lighting, a genuinely consequential fact of daily and agricultural life.

Sources AstronomyAndrew Fraknoi, David Morrison, and Sidney C. Wolff (OpenStax) with Wicca: A Guide for the Solitary PractitionerScott Cunningham

The waning gibbous covers elongation from a hundred and eighty degrees to two hundred and seventy, between full moon and last quarter, with more than half the disc lit and the illuminated portion shrinking. It is the mirror of the waxing gibbous in appearance and its opposite in timing: the Moon now rises after sunset and is highest in the small hours.

The phases are produced by the changing angle between the Sun, the Earth and the Moon, and the quantity that defines them is elongation, the Moon's angular distance from the Sun as seen from the Earth. The complete round from one new moon to the next is the synodic month, about 29.53 days, and it is longer than the sidereal month of about 27.32 days in which the Moon returns to the same place among the stars, because the Earth has moved along its orbit in the meantime and the Moon must travel further to catch up.

The waxing and waning halves of the cycle are geometrically symmetrical and culturally are not. A very large number of traditions treat the growing Moon and the diminishing Moon as carrying different qualities, and the Panchanga formalises the division: the bright fortnight, shukla paksha, runs from new to full, and the dark fortnight, krishna paksha, from full back to new, each of fifteen tithis, and the same tithi name occurs once in each with a different character.

Sources AstronomyAndrew Fraknoi, David Morrison, and Sidney C. Wolff (OpenStax) with The Indian CalendarRobert Sewell and Sankara Balkrishna Dikshit