Moon Phase Calculator — Any Date, Real Astronomy

Real lunar arithmetic: age from a known new moon, illumination from the phase angle, and the next new and full moon dates.

Quick answer: Calculate the moon phase for any date: lunar age in days, percentage illuminated, waxing or waning, the phase name and the next new and full moons — using real synodic-month maths.

Date

–illumination

–lunar age

–phase

–trend

How to use

Pick any date.
Read the age, illumination and phase.
Copy the summary.

About this tool

Unlike the numerology tools on this page, this one is straight astronomy. The moon's synodic month is 29.530588 days, so its age on any date is the elapsed time since a known new moon, taken modulo that period. Illumination follows from the phase angle, and the phase name follows from the age. The tool also projects the next new moon and full moon by stepping forward in synodic increments. Results match published almanacs to within a few hours, which is the accuracy limit of the mean-synodic method.

FAQ

How accurate is it?

Within a few hours. It uses the mean synodic month, so the moon's orbital eccentricity causes small variation from the true moment.

What is lunar age?

Days since the last new moon, from 0 to 29.53.

What does illumination mean?

The fraction of the moon's visible disc that is lit, from 0% at new moon to 100% at full.

Why does my date differ from another site?

Time zone. This tool uses your browser's local time; almanacs often quote UTC.

Is my data saved?

No.

Is this astrology?

No — this is astronomical calculation, not a belief system.

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Moon Phase Calculator — Any Date, Real Astronomy

How to use

About this tool

FAQ

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