Calculate and visualize the Moon's phase for any date. The lunar cycle is 29.53059 days — a synodic month.
Select Date
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Illumination
Monthly Calendar
How it works: The Julian Day Number is used to calculate the Moon's age in its synodic cycle.
The algorithm uses the known new moon epoch (Jan 6, 2000 was a new moon at 18:14 UTC, JD 2451549.75)
and divides the elapsed days by the mean synodic period (29.53059 days).
The phase angle determines which part of the Moon's disk is illuminated.