On this day the Moon was in a Waning Gibbous. During this phase the Moon can be seen in the early morning daylight hours on the western horizon. This is the first phase after the Full Moon occurs. It lasts roughly 7 days with the Moon’s illumination growing smaller each day until the Moon becomes a Last Quarter Moon with an illumination of 50%. The average Moon rise for this phase is between 9pm and Midnight depending on the age of the phase. The moon rises later and later each night setting after sunrise in the morning.
Visit the May 2017 Moon Phases Calendar to see all the daily moon phase for this month.
The Waning Gibbous on May 11 has an illumination of 100%. This is the percentage of the Moon illuminated by the Sun. The illumination is constantly changing and can vary up to 10% a day. On May 11 the Moon is 15.3 days old. This refers to how many days it has been since the last New Moon. It takes 29.53 days for the Moon to orbit the Earth and go through the lunar cycle of all 8 Moon phases.
There are 8 lunar phases the Moon goes through in its 29.53 days lunar cycle. The 4 major Moon phases are Full Moon, New Moon, First Quarter and Last Quarter. Between these major phases, there are 4 minor ones: the Waxing Crescent, Waxing Gibbous, Waning Gibbous and Waning Crescent. For more info on the Moon Cycle and on each phase check out Wikipedia Lunar Phase page.