Waning gibbous moon from the International Space Station

© NAS

Waning gibbous moon

The gibbous moon is one of the various phases that the Moon goes through during its monthly lunar cycle. It's when the Moon is more than half full, but not quite fully illuminated, when you look at it from the perspective of Earth. This phase happens twice each month during the waxing gibbous phase and the waning gibbous phase. With some exceptions, the waning gibbous moon rises after sunset but before midnight and doesn’t set until after sunrise. When the Moon is in the waning gibbous phase, the sunlit part of the Moon is decreasing from 99.9% to 50.1%. Waning means that it is shrinking and getting smaller, while gibbous refers to the oval-to-round shape that appears.