What Is a Blue Moon? A Simple Explanation

The closest neighbor to Earth, the moon, leaves us with many questions unanswered. Full moons have many different names, but what is a blue moon. We answer the question and find out when we can next see a blue moon.

The name blue moon is a little misleading as the moon doesn’t turn into a blue. If you were looking forward to seeing a bright blue moon, then you will be left disappointed.

We call a moon blue when a full more occurs for the second time of the calendar month. Or when the third full moon occurs of the astronomical season.

Blue Moon in February?

As the lunar month is 29.5 days long, it will never be possible to have a blue moon in February. The reason is February only has 28 days and 29 days in a leap year.

The other 11 calendar months of the years are longer than the 29.5 days a lunar month, so it is possible to have a blue moon on any other month apart from February.

How Often Do Blue Moons Happen?

Blue moons are not an everyday event; they happen on average every 2.7 years. If a full moon falls at the start of the month, a second moon may be squeezed in.

When we use the term “blue moon,” something rarely happens, and people have said this is why it is called a blue moon as it rarely happens.

A blue moon shows us that our calendar is arbitrary and has no connection to the moon’s natural cycle.

Different Definitions of Blue Moon

The astronomical definition of a blue moon was when the third full moon of the astronomical season occurs.

It was a mistake by James Hugh Pruett (1886–1955) when he didn’t understand the astronomical seasonal calendar and wrote that a blue was “when a full more occurs for the second time of the calendar month.” Prestigious astronomy publications then picked up the mistake.

After this, it was used as a source and printed in many high-profile publications, and the misinformation spread. Trivia board games even picked it up the incorrect information over the years.

Will the Moon Ever Look Blue?

Even though the moon doesn’t turn blue every time, a blue moon happens despite the name suggests. There is a time when the moon does turn blue; it doesn’t have to be a full moon to happen.

When the atmosphere is filled with dust or smoke particles, they scatter the atmosphere’s red light. What happened is with the red light being scattered, it makes the moon appear blue. This phenomenon is called Mie scattering and can occur after a dust storm of forest fires.

When Is the Next Blue Moon?

The blue moon’s incorrect definition, but the wildly used method of two full moons in a month, is on 2020 31 October.

The next three blue moons using the two in a month method are below:

2023 31 August
2026 31 May
2028 31 December