Blue Moon 2026: Why it's special and what makes it different

Skywatchers are in for a rare celestial treat this month as a Blue Moon is going to light up the night sky on May 31.

This upcoming event is attracting attention because it is one of the rare occasions when two full moons occur within the same calendar month, something that happens only once every few years. Here's more about it.

Here's what the Blue Moon really is

A Blue Moon refers to an “extra” full moon that appears due to the mismatch between the lunar cycle and the calendar year.

The Moon takes roughly 29.5 days to complete its cycle, while calendar months contain 30 or 31 days. Occasionally, this timing allows two full moons to fit into a single month. When this happens, the second full moon is known as a “monthly Blue Moon”.

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This month’s Blue Moon falls into that category because one full moon appeared earlier in the month, while the second will occur at the very end of May.

Why this Blue Moon, in particular, is special?

Blue Moons are relatively uncommon, occurring roughly once every two to three years. The phrase “once in a blue moon” itself comes from this rarity.

What makes this month’s event particularly notable is that it is the only Blue Moon expected this year. Astronomers note that monthly Blue Moons can only happen in months with 30 or 31 days, which is why February can never experience one.

The event also highlights the curious way human calendars align imperfectly with lunar cycles.

Did you know there are two different types of Blue Moon?

Interestingly, not all Blue Moons are defined the same way.

The most widely recognised definition describes the second full moon in a calendar month. However, astronomers also use an older “seasonal” definition.

Under this system, a Blue Moon is the third full moon in a season that contains four full moons instead of the usual three.

This difference is what makes Blue Moons slightly confusing - and scientifically intriguing.

Will the Moon actually turn blue on May 31?

Despite the name, the answer is no.

A Blue Moon generally looks no different from any other full moon. The term refers purely to timing, not colour.

However, on very rare occasions, atmospheric conditions caused by volcanic eruptions, smoke or dust particles can scatter light in a way that gives the Moon a bluish appearance. This phenomenon is extremely uncommon and unrelated to the Blue Moon event itself.