The blue moon is the second of two full moons in a single month. Each month usually hosts only one full moon, but blue moons sometimes arise because the lunar cycle is 29.5 days long — just short of the length of an average calendar month. This difference means that some months see two full moons.
That is exactly what happened this month: The first full moon popped up on Aug. 1 and the second on Wednesday.
What is a blue supermoon?
A supermoon occurs when the full moon phase of the lunar cycle syncs up with the perigee, or when it is nearest to the Earth. Supermoons appear brighter and bigger than regular full moons. According to NASA, the apparent size increase is 14 percent, which is about the difference between a nickel and a quarter.
Will the moon actually look blue?
No. The term “blue moon” doesn’t really describe its color; it’s mostly its usual milky gray. (Certain phenomena, like wildfires and volcanic eruptions, can tint the moon blue, the same visual effect that gave North American skies an orange hue this summer.)
According to NASA, the term “blue moon” used to refer to the third full moon in a season that had four full moons. The newer definition — the second full moon in a month — was coined by the magazine Sky & Telescope in 1946.