What is a blue moons?

Answer 1

Astronomy

A "blue moon" is the second full moon to occur in a calendar month. It happens rarely, hence the phrase, "Once in a blue moon." Because full moons occur every 29.5 days, a second full moon can occur if the first one is early enough in a month.

Since a year has 11 days more than the 12 lunar months, the extra days accumulate, so that every two or three years (on average about every 2.7154 years) there is an extra full moon. The extra moon is also called a "blue moon".

The original use of the term blue moon was by the Farmers Almanac, to mean the third of four full moons in a "season." This nomenclature allowed the final full moon to be used in various seasonal calculations.

Hypothetical Planet

Aurelia and Blue Moon are hypothetical examples of a planet and a moon on which extraterrestrial life could evolve. The fictional satellite, called Blue Moon, of a hypothetical planet (Aurelia) was an exercise underwritten by National Geographic.

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Answer 2

A "Blue Moon" is when two full moons occur in a 30 or 31 day month and this occurs about every three years. A "Blue Moon" is not actually blue despite the name.