Moon phases: a practical introduction
Explore the cycle of lunar phases and try a simple approximate calculator.
What changes during the cycle
The Moon reflects sunlight. As its position relative to Earth and the Sun changes, we see different portions of its sunlit half. The familiar sequence runs from new Moon through waxing phases to full Moon, then through waning phases toward the next new Moon. Waxing means the illuminated portion is increasing; waning means it is decreasing.
Eight useful labels
New Moon, waxing crescent, first quarter, waxing gibbous, full Moon, waning gibbous, last quarter, and waning crescent describe the cycle. These labels are a guide to appearance, not eight equal periods of astronomical motion. A quarter Moon has roughly half its visible disk illuminated; the name refers to progress through the cycle.
Try a date
Our phase calculator estimates the cycle at 12:00 UTC on your selected date using a fixed mean month. It offers approximate lunar age and illumination for learning. Use the linked NASA phase tables when you need calculated event times. This tool does not determine Moon signs, visibility, moonrise, or moonset.
Sources and further reading
NASA: Moon phases explains the cycle. NASA: phase tables 1901–2000 supplies the reference new Moon and mean lunation used here. NASA lists times as Universal Time; this educational tool uses UTC at minute precision.