What is a moon phase?
A moon phase is the shape of the lit part of the Moon as seen from Earth, set by the angle between the Sun and Moon. The cycle runs from new Moon through waxing crescent, first quarter, waxing gibbous, full Moon, and back through the waning phases over about 29.5 days.
How the moon phase is calculated
This calculator measures the angular distance between the Sun and Moon for the date you choose, then maps it to one of the eight phases and an illumination percentage. The numbers come from Swiss Ephemeris astronomy, so they match what you see in the sky.
Moon phase and the Moon sign
Alongside the phase, the tool shows the zodiac sign and degree the Moon occupies that day. The phase describes the light; the sign describes the Moon position in the zodiac. Together they give a fuller picture of the lunar day.
Using the moon phase calculator
Pick any date to see its phase, illumination, and Moon sign, past, present, or future. The phase is a description of the sky, not a forecast. For your personal Moon, try the Moon sign calculator.