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.
Blue Moon in 2026
In 2026, there will be a Blue Moon on May 31, 2026. This happens because May 2026 will have two full moons:
May 1, 2026: First full Moon (Flower Moon)
May 31, 2026: Second full Moon (Blue Moon).
The second full Moon in May 2026 makes this a monthly Blue Moon.
When to See the May 2026 Blue Moon?
On May 31, 2026, the Moon will reach full phase at around 08:45 UTC, but the exact local date might vary slightly depending on your time zone.
If you’re in India (UTC+5:30), for example, the Full Moon will still be visible on May 31, rising just after sunset. Though it won’t be blue in color, it will be the second full Moon of May thus called as a Blue Moon.
Blue Moons from the year 2026 to 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 |
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.
When is the next Blue Moon?
The Next Blue Moon is on May 31, 2026.
Are Blue Moons Rare?
Yes, Blue Moons are uncommon, but not extremely rare. On average, a Blue Moon occurs once every 2 to 3 years.
Does a Blue Moon actually look blue?
No. A Blue Moon looks the same as any other full Moon. The term refers to timing, not color.
What is the difference between a Blue Moon and a Supermoon?
A Blue Moon is defined by timing, while a Supermoon occurs when a full Moon happens near the Moon’s closest point to Earth, making it appear slightly larger and brighter.
Is a Blue Moon visible worldwide?
Yes. A Blue Moon is visible from anywhere on Earth where the full Moon is above the horizon at that time.