Calculating the Moon Phase In Your Head
for the year 2001 only

step 1:		Start with 0.
step 2:		Add the number for the month.
step 3:		If the number for the month is even, add ½.
step 4:		If the number for the month is 9 or 11, add 1.
step 5:		If the number for the month is 1 or 2, add 2.
step 6:		Add the number for the day of the month.
step 7:		If your number is greater than 29½, add ½ and subtract 30.
step 8:		Add 2.
step 9:		Add ¼.
step 10:		If your number is greater than 29½, add ½ and subtract 30.

You now have the age of the moon in days for midday (UT) of your chosen date, thus your result may be interpreted as follows.

This algorithm is accurate within ½ day for all of the year 2001.  For super accurate results, use the source formula from the specifications on page 2 of the Moonstick Instructions.

January 14, 2001 –  I have checked this algorithm for accuracy on all of its valid dates.  No accuracy violations were found.  –author

This page is part of the Moonstick Information Site.
copyright © 2000 Sean Barton, all rights reserved