A blue moon is rising today, May 31, 2026, offering skywatchers a rare celestial event. Despite its name, the moon will not appear blue. Instead, it is the 13th full moon of the calendar year, an occurrence that happens roughly every two to three years. This year's blue moon is also a micromoon, meaning it will appear slightly smaller and dimmer than usual.
What is a blue moon?
A blue moon is defined as the 13th full moon in a calendar year. According to Royal Museums Greenwich, each lunar phase cycle takes about 29.5 days, totaling 354 days for 12 cycles—just short of a full year. This discrepancy occasionally results in an extra full moon, which is called a blue moon because it does not fit the traditional naming pattern (e.g., wolf moon, flower moon, harvest moon).
Why are blue moons not blue?
The term "blue moon" does not refer to color. The name likely originates from a mispronunciation of the Old English word "belewe," meaning "to betray." Thus, a blue moon "betrays" the usual pattern of one full moon per month. There are two other definitions: an astronomical blue moon is the third of four full moons in a season, while a popular definition describes it as the second full moon in a calendar month with two full moons.
How often do blue moons occur?
Blue moons occur every two to three years. The last blue moon was on August 19, 2024. After today, the next blue moon will be on May 20, 2027. Occasionally, two blue moons happen in the same year, as in 2018 and expected again in 2037.
Can you see the blue moon in the UK today?
The blue moon will peak at approximately 9:45 am BST on May 31. However, the Met Office has forecast showers and cloudy conditions across the UK following a record-breaking heatwave. Since this is also a micromoon, visibility may be reduced, especially in rainy areas. Early risers are encouraged to look for the moon before clouds thicken.
Upcoming full moons in 2026
If you miss today's blue moon, the following full moons are scheduled: strawberry moon on June 30, buck moon on July 29, sturgeon moon on August 28, harvest moon on September 26, hunter's moon on October 26, beaver moon on November 24, and cold moon on December 24.
