There's an upcoming blue moon tomorrow. Some of my pagan friends are doing something extra special. I don't think there's anything particularly special as I'm getting away from using the calendar month. Here are some definitions of blue moon:
A literal blue moon occurs when the (not-necessarily-full) moon looks blue due to dust or other foreign objects in the atmosphere. One may see this type of blue moon after a volcanic eruption.
This blue moon occurs when there are 4 full moons in a season. Equinoxes and solstices mark the beginning of the season. The 3rd full moon is the blue moon.
The modern definition is the 2nd full moon in a calendar month. It really isn't all that rare; it happens about every 2.5 years or so. It is this definition that is used for tomorrow's full moon.
If you're into astrology, the zodiacal blue moon is the 2nd of 2 full moons in the same sign.
Regardless of which blue moon you prefer, all full moons are magical.
PS I wonder why new moons aren't as special. If so, what would they be called?