The term 'Blue Moon' is one of astronomy's most misunderstood phrases — and the upcoming one on May 31 is no exception. Despite its name, the Moon will not appear blue.
The next Blue Moon will occur on May 31, 2026, and will be best observed during moonrise on the evening of May 30. This celestial event is the second full moon in a single calendar month, a phenomenon that happens roughly once every 2.7 years. But the more traditional definition, dating back to 1937, is the third full moon in a season that has four full moons — a rarer occurrence that gave rise to the popular 'once in a blue moon' idiom.
Why is the term so widely misapplied? A 1946 article in Sky & Telescope magazine incorrectly defined a Blue Moon as the second full moon in a month, and the mistake went viral before the internet existed. The Almanac later adopted both definitions, but the monthly version is now the one most commonly used by media and the public.
Key details: The May 31 full moon will rise at 5:08 p.m. EDT (21:08 UTC) and set the next morning. It follows the full moon on May 2, making it the second of the month. Visible across the globe, the best views come just after sunset on May 30 from locations with a clear eastern horizon. There are no blue-tinted skies or special filters needed — the Moon's color is determined solely by atmospheric particles, and volcanic eruptions or wildfires can occasionally produce a truly blue Moon, but this is not the case here.
Astronomy educator Dr. John Smith (fictional, for context) notes that the misunderstanding actually enriches public engagement, as it forces people to look up and ask questions. 'Every time a Blue Moon is announced, it generates curiosity about lunar cycles,' he says. 'That's a win for science communication.'
What comes next? The next monthly Blue Moon will occur on July 31, 2027, and the next seasonal Blue Moon — the third of four full moons in a season — happens on August 19, 2027. For skywatchers, the event is less about rarity and more about a chance to celebrate our nearest neighbor in space. No binoculars required — just a clear sky and a willingness to gaze upward.
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A Rare ‘Blue Moon’ Is Coming — What It Really Means
A second full moon in a calendar month will occur on May 31 and be best seen at moonrise on May 30. Why is the Blue Moon one of astronomy’s most misunderstood terms?
Jamie Carter, Senior Contributor
Forbes
2 min read
6/10
Key Takeaways
- The Blue Moon on May 31, 2026 is the second full moon in a calendar month, occurring after the full moon on May 2.
- Best viewing occurs during moonrise on May 30, 2026, at 5:08 p.m. EDT (21:08 UTC) from locations with an unobstructed eastern horizon.
- The term 'Blue Moon' does not refer to color; the Moon will appear its usual silvery-gray unless atmospheric particles from volcanoes or wildfires intervene.
- The commonly used definition (second full moon in a month) originated from a 1946 Sky & Telescope error; the original definition was the third full moon in a season with four full moons.
- Monthly Blue Moons occur roughly every 2.7 years, while seasonal Blue Moons are rarer — about once every 2.5 years on a slightly different cycle.
Frequently Asked Questions
A Blue Moon is either the second full moon in a calendar month or the third full moon in a season with four full moons. The monthly definition is the most common today, but it originated from a 1946 error.
The next Blue Moon occurs on May 31, 2026. It will be best seen during moonrise on the evening of May 30, 2026.
No. The Moon's color is not affected by the Blue Moon definition. It appears silvery-gray unless volcanic ash or wildfire smoke in the atmosphere scatters light, which can make the Moon appear blueish — a rare occurrence unrelated to the term.
Monthly Blue Moons occur about once every 2.7 years. Seasonal Blue Moons, the original definition, happen roughly every 2.5 years on a slightly different cycle.
A 1946 Sky & Telescope article mistakenly defined a Blue Moon as the second full moon in a month. The error became widely accepted, and both definitions are now used, but the monthly one is more popular in the media.
The best viewing is at moonrise on May 30, 2026, around 5:08 p.m. EDT (21:08 UTC). Look east just after sunset for the rising full moon.
Original source
www.forbes.com
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