20 December 2006
Do you own a monthly calendar? Check in the corners of the dates to see if it indicates the moon phase. Yes? Chances are it's wrong. I've noticed that roughly half (give or take 25%) of the calendars I've owned that had moon phases on them were wrong. If you want to know the actual real phases of the moon, check out the supremely accurate US Naval Observatory moon phase calculator, or for a simpler version StarDate Online's appears to be correct as well. The USNO also has the best sunrise/set calculator (as well as some additional info).