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TL;DR
- The next blue moon is May 31, 2026 (8:45 UTC) – a monthly blue moon and the smallest full moon of the year.
- A blue moon is either the 2nd full moon in a calendar month or the 3rd full moon in a season with four full moons.
- Blue moons happen roughly once every 2–3 years.
- It won’t look blue – that’s just a name.
Blue Moons Dates 2026-2036
| Year | Full Moon | Blue Moon |
|---|---|---|
| 2026 | May 1, 2026 | May 31, 2026 |
| 2028 | December 2, 2028 | December 31, 2028 |
| 2031 | September 1, 2031 | September 30, 2031 |
| 2034 | July 1, 2034 | July 31, 2034 |
What is a Blue Moon?
A Blue Moon refers to an extra full Moon that appears within a defined time period. The term is used in two scientifically accepted ways in astronomy, both based on lunar timing rather than appearance.
In simple terms, a Blue Moon happens when the Moon’s natural cycle does not align perfectly with the calendar months or astronomical seasons.
Types of Blue Moons
Astronomers recognize two types of Blue Moons, each based on a different definition.
Monthly Blue Moon (Calendar Definition)
A monthly Blue Moon is the second full Moon in a single calendar month.
This definition is the most widely used today. It became popular in the mid-20th century and is now commonly referenced in calendars, media, and public discussions. The May 31, 2026 Blue Moon falls under this category.
Seasonal Blue Moon (Astronomical Definition)
A seasonal Blue Moon is the third full Moon in an astronomical season that contains four full Moons instead of the usual three.
Astronomical seasons are defined by solstices and equinoxes, not calendar months. To preserve traditional Moon naming conventions, astronomers label the third full Moon of such a season as the Blue Moon. This definition appears in older astronomical almanacs and remains scientifically valid.
Why Do Blue Moons Occur?
The Moon completes one full cycle of phases in 29.53 days, known as a lunar month. In contrast, most calendar months last 30 or 31 days.
This mismatch allows: Two full Moons to occur in one calendar month, or Four full Moons to fit within a single astronomical season
How Often Does a Blue Moon Happen?
On average, a monthly Blue Moon occurs once every 2–3 years and a seasonal Blue Moon also occurs about once every 2–3 years
This pattern repeats roughly every 19 years, a cycle known as the Metonic Cycle, which links lunar phases to calendar dates.
Does a Blue Moon Actually Look Blue?
No. A Blue Moon looks just like any other full moon, appearing white, silver, or pale yellow depending on its position in the sky and local atmospheric conditions. The term “Blue Moon” refers to the timing of the full moon, not its color.
However, there have been rare occasions when the Moon genuinely appeared blue. This can happen when large wildfires or volcanic eruptions release smoke and ash particles of a specific size into the atmosphere.
These particles scatter red wavelengths of light while allowing more blue light to pass through, giving the Moon a bluish tint. Historical reports describe blue-colored moons following major events such as the 1883 eruption of Krakatoa and the 1980 eruption of Mount St. Helens.
For the Blue Moon of May 31, 2026, observers should not expect any unusual coloration. Despite its name, it will appear much like any other full moon.
Blue Moon vs. Supermoon: What’s the Difference?
A Blue Moon and a Supermoon are entirely different astronomical events.
A Blue Moon is defined by timing. It occurs either as the second full moon within a single calendar month or, under the seasonal definition, as the third full moon in a season containing four full moons.
A Supermoon, by contrast, is defined by distance. It occurs when the full moon takes place near perigee, the point in the Moon’s orbit closest to Earth. As a result, the Moon appears slightly larger and brighter than usual.
On rare occasions, the two events can occur together. The full moon of August 30, 2023, was both a Blue Moon and a Supermoon, creating what is commonly known as a “Super Blue Moon.” This combination will not occur again until 2037.
Without knowledge of the calendar, a Blue Moon is visually indistinguishable from any other full moon. Its significance comes entirely from its unusual timing.
See Super Moon Dates 2026 🌕
Is the 2026 Blue Moon Special?
Yes, but for a reason many people may not expect.
The Blue Moon on May 31, 2026, will also be a Micromoon. A Micromoon occurs when the full moon takes place near apogee, the point at which the Moon is farthest from Earth in its orbit. On that date, the Moon will be approximately 406,134 kilometers from Earth, compared with its average distance of about 384,472 kilometers.
This makes it the smallest full moon of 2026. It will appear slightly smaller and about 7 percent dimmer than an average full moon. Compared with a Supermoon, it may be roughly 25 to 30 percent dimmer.
The combination of a Blue Moon and a Micromoon on the same night is relatively uncommon, leading some astronomers and skywatchers to refer to the event as a “Blue Micromoon.”
Although the size difference will be difficult to detect with the naked eye, the event remains an interesting astronomical rarity. In a year filled with full moons, the rarest-sounding one will also be the smallest.
FAQ’s ❓
What is a blue moon?
A blue moon is either the second full moon in a calendar month (monthly blue moon) or the third full moon in an astronomical season that has four full moons (seasonal blue moon). Both definitions are valid.
How often does a blue moon occur?
A blue moon occurs roughly once every 2 to 3 years. In every 19-year Metonic cycle, there are 7 monthly blue moons and 7 seasonal blue moons – so about 14 total over 19 years.
Does a blue moon actually look blue?
No. It looks like any other full moon. The moon can appear blue after major volcanic eruptions or wildfires (due to specific atmospheric particles), but that’s unrelated to the blue moon calendar definition.
What is the difference between a monthly and seasonal blue moon?
A monthly blue moon is the second full moon in a single calendar month. A seasonal blue moon is the third full moon in an astronomical season (spring, summer, autumn, or winter) that contains four full moons instead of the usual three.
Is a blue moon rare?
a blue moon happens every 2–3 years. The phrase “once in a blue moon” suggests rarity, but you’ll see roughly 8–10 blue moons in a typical lifetime.
What is the difference between a blue moon and a supermoon?
A blue moon is defined by timing (second full moon in a month, or third in a four-full-moon season). A supermoon is defined by distance (full moon near perigee, appearing larger and brighter). They can occasionally coincide, as in August 2023.