Many witches are drawn to the Moon, and sometimes for good reason! In my beliefs, the Moon holds a particular type of energy that can be used to help fuel my spellwork. This energy waxes and wanes, just like the phases of the Moon herself, and the associations of each phase are different. A Full Moon, though, has the most potent, all-encompassing energy of all the phases.
A blue moon is not actually a blue moon. The moon doesn’t turn blue — even though that would pretty neat for a blue moon — but there are two different definitions for the term “blue moon”. The older definition says that a blue moon refers to the third full moon in a season with four full moons. It has something to do with correcting the lunar cycle and making sure that when people were planting and growing their crops by the moon calendar, that seasons didn’t “come too early”.