Waning Gibbous Lunar Phase At 86% Illumination Stock Image

The Moon appears to be a circular disk which, at any specific time, is illuminated to some degree by the Sun’s light. When we refer to the percent illumination, we are referring to the percent of that circular disk which is lit up. So, when it’ s a New Moon, the percent illuminated is 0; at First and Last Quarters it is 50%; and at Full Moon it is 100%. During the crescent phases the percent illuminated is between 0 and 50% and during gibbous phases it is between 50% and 100%.