There Are Two Types Of
Blue Moons but unfortunately neither has anything to do with color.
The Seasonal Blue Moon Is The
Traditional definition of a Blue Moon and refers to the third full moon in a season that has four full moons according to NASA.
Whilst The Second Definition
borne out of a misunderstanding of the first is a monthly Blue Moon which refers to the second full moon within a single calendar month.
The Monthly Blue Moon Is
Nowadays considered the second definition of a Blue Moon rather than a mistake, according to Time and Date.
The Moon Phases Actually Take
29.5 days to complete which means it takes just 354 days to complete 12 lunar cycles.
So Every 2.5 Years
Or so a 13th full moon is observed within a calendar year.
This 13th Full Moon
doesn't conform to the normal naming scheme and is referred to as the Blue Moon.