The Blue Moon Phenomenon: What Does It Really Mean?

Have you heard the expression "once in a blue moon"? It refers to something rare, and for good reason.

Astronomical Definition

A Blue Moon is usually not actually blue. The term refers to the second full moon in a single calendar month. Since the lunar cycle is 29.5 days, this happens only every 2 to 3 years.

Can the Moon Turn Blue?

Yes, but it's very rare! This only happens if there are dust or smoke particles of a specific size in the atmosphere, usually after major volcanic eruptions or forest fires.