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Science, Climate & Environment

Moon Phase Calculator

Calculate the Moon's phase and illuminated fraction at an exact instant, plus the next four primary lunar phases.

Free · Private · Runs in your browser

Lunar phase

Calculate the Moon's phase

Choose a local date and time to see the geocentric phase angle, illuminated fraction, and next four primary phases.

The phase is geocentric, so coordinates are not required. The time zone controls which exact instant your local input represents.

The lunar phase, illumination, and next primary phases will appear here.

What the calculation means

Phase angle is the geocentric ecliptic-longitude difference between the Moon and Sun: 0° is new moon, 90° first quarter, 180° full moon, and 270° third quarter. The familiar eight phase names classify the angle into 45° sectors.

Scope and precision

The result describes the Moon as viewed from the center of Earth. Coordinates are unnecessary for phase, but local rise, set, apparent orientation, weather, and horizon visibility depend on location and are outside this tool.

Version

Calculation version 1.0.0; astronomy-engine 2.1.19. Inputs and results remain in the browser.

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