To look up the phase of the moon for any (Common Era) date,
just fill out the form below, then hit “Find Phase.”

The waning moon.

At 01:20:21 UT Thursday 23 September 2021
the moon’s phase is

WANING GIBBOUS (95.70% full)

Some factors that go into this equation:

Universal Time is 1.35583333333333 in decimal hours.
The Julian date is 2459481.45695825.
The sun’s ecliptic longitude is 180.243971492849 degrees.
Its mean anomaly is 259.3577763952 degrees.
The moon’s mean longitude on 00 January 1990 was 318.351648 degrees.

These calculations incorporate the switch to the English New Style (N.S.)—i.e., Gregorian— calendar after Wednesday, 02 September 1752; the next day became Thursday, 14 September, skipping eleven days. (Please also note that, while fairly accurate, these calculations remain a bit buggy.)

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