To look up the phase of the moon for any (Common Era) date,
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The full moon.

At 20:26:00 UT Sunday 22 August 2021
the moon was


Some factors that go into this equation:

Universal Time is 20.45 in decimal hours.
The Julian date was 2459449.49843745.
The sun’s ecliptic longitude was 149.933037886915 degrees.
Its mean anomaly was 228.6012324448 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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