To remember the phase of the Moon in 2021, take this year's Magic New Moon Number of 16 and subtract the Month. To within about a day, the New Moon falls on January 15, February 14, March 13, April 12, ..., December 4. Add a week for each phase, i.e., +7 for First Quarter, +14 for Full Moon, and +21 for Last Quarter. Close enough!

For 2022, the Magic Full Moon number is 19; for 2023, the Magic New Moon number is 23. Is there a long-term pattern to learn that works for decades? Hmmm ...

(cf Body Mnemonic (2004-12-04), Mnemonic Principles of Taiji (2014-03-24), ...) - ^z - 2021-04-30