Full Moon Calendar
Enter a year and the calendar lists every full moon in it with dates, counts them, and flags the years that get thirteen - the blue moon years. Because the list is computed from the 29.5306-day cycle rather than copied from a printed table, any year from 1900 to 2100 answers instantly, including years no almanac ever bothered to print.
Most full moon pages are one frozen year per page, tuned for ads. This one answers the question people actually have - when are the full moons - for any year at once, and says plainly that the simple cycle carries about a day of tolerance, so you know when to trust it for a moonlit walk and when to check an observatory for an eclipse.
How to use
- Type a year (this year is pre-filled).
- Read the dated list and the count.
- Watch for the extra-moon flag - that year has a blue moon.
Frequently asked questions
How many full moons are in a year?
Usually twelve - one synodic month is 29.53 days versus about 30.4 days per calendar month, so a full moon lands roughly every month. Thirteen arrive when one falls in the first days of January, and those years are marked here.
What is a blue moon?
The common modern meaning is the second full moon in one calendar month, which happens in the same years that fit thirteen full moons. The calendar flags those years so you know where to look.
How precise are these full moon dates?
Within about a day of official almanac times, because the simple synodic cycle ignores the orbit's elliptical speed-ups. For eclipse nights or minute-precise timing, an observatory table is the better tool.
Can I see full moons for a past year?
Yes - any year from 1900 to 2100 works, which printed calendars never bother covering.