On this day the Moon was in a First Quarter phase. This phase occurs roughly 7 days after the New Moon when the moon is one quarter of the way through its orbit around the earth. Exactly half the moon will be illuminated and half dark. On the day of the First Quarter phase the moon is high overhead at sunset and is visible until mid-night when it sets in the west. The First Quarter phase is a one-day event and in the following days enters a Waxing Gibbous phase becoming more illuminated each day until the Full Moon.
Visit the September 2017 Moon Phases Calendar to see all the daily moon phase for this month.
The First Quarter on September 28 has an illumination of 54%. 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 September 28 the Moon is 7.72 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.