Moon age: Number between 0 and 30=0 (recall that a lunation is 29.52 days); meaning:
Moon Phase
Day Numb. (rounded)
Day Numb.
🌑 New Moon
0
0
🌓 First Quarter Moon
7
7.38
🌕 Full Moon
15
14.76
🌗 Last Quarter Moon
22
22.14
🌑 New Moon
30
29.52
Calculate the moon age for any date YYYY-MM-DD
Algorithm (simplified version of an algorithm by John Conway)
Year YYYY
This algorithm is valid for years 2000 to 2018 (from 2000-01-01 to 2018-12-31). If outside those years, add or subtract repeatedly 19 years till the year is in the range 2000 to 2018 (this uses the Metonic Cycle of 19 years)
Take the last two places of the year and add 2 (you can think of this as adding the 4 digits such that the last two are considered together)
Multiply by 11
Subtract repeatedly 30 till the number is between 0 and 29
Month MM
Add the number of the month (a number between 1 and 12; if the month is January or February; add additionally +1)
Day DD
Add the number of the day
Result
Subtract repeatedly 30 till the number is between 0 and 29
The result is the moon age (with a maximum error of +/- 2 days)