Calendar rarity · Europe/London rule
When is the next Blue Moon?
The next monthly Blue Moon in Europe/London is Sun, 31 Dec 2028, reaching full phase at 31 December 2028 at 16:48 GMT.
The monthly definition used by this calendar
This site calls the second full Moon in one Europe/London calendar month a Blue Moon. Time zone matters: an instant close to midnight can belong to a different civil date elsewhere, so a UTC list can occasionally disagree with a UK calendar.
The phrase does not describe colour. A genuinely blue-looking Moon is a separate, unusual atmospheric effect caused by particles that filter light.
Long-range calendar
Upcoming monthly Blue Moons
- Sun, 31 Dec 2028
- Tue, 30 Sept 2031
- Mon, 31 Jul 2034
- Sat, 31 Jan 2037
- Tue, 31 Mar 2037
The older seasonal definition
Another rule calls the third full Moon in an astronomical season containing four a Blue Moon. It is not interchangeable with the monthly rule. For example, the next seasonal Blue Moon is Thu, 20 May 2027, while the next monthly one in Europe/London is Sun, 31 Dec 2028. The calendar uses the monthly rule consistently for year counts and badges.
- — third of four full Moons in the season
- — third of four full Moons in the season
- — third of four full Moons in the season
- — third of four full Moons in the season
- — third of four full Moons in the season
The monthly rule spread from James Hugh Pruett’s March 1946 Sky & Telescope article, which interpreted an older Maine almanac’s seasonal rule as a second full Moon in a month. The phrase “once in a blue Moon” has older uses for rarity. Sky & Telescope’s history of the two rules.