While my astrological style leans away from tradition, my dedication to the traditional meaning of Blue Moon has been, for the most part, unwavering. I feel like a small fairy or star being, or crab dies every time the usage of "blue moon" isn't understood or acknowledged. So far in 2018, it has been said we have had two blue moons, though technically we haven't had one yet and the last one wasn't since August 2013.
The phrase "once in a blue moon" means a rare occurrence, though depending on the definition it can happen fairly frequently. This confusion is quite understandable as there are four types of Blue Moons (to my knowledge) with meanings that have evolved over the past century.
1) Two full moons in the same calendar month. Though this is perhaps the most common usage of the term, I'm not a fan because it fails to acknowledge the oddity of the Gregorian calendar that doesn't match the lunar calendar or New Moon happenings. It also makes it less rare because it happens more frequently, we've already had two in one year!?
2) Blue colored Moon because of dust or smoke particles. I don't understand the science here and it isn't predictable, so I will leave this here...not sure I want to see a blue moon of this type.;)
3) Two consecutive full moons in same astrological sign. This one also isn't spoken about often though would certainly be more rare than the first example.
4) Four full moons in a season instead of three. That last full moon is an added bonus and was determined by the Farmer's Almanac and seasons of Earth, which I find makes the most sense. It is much more rare, around every three years, and apparently was misunderstood by a journalist in 1946 and printed in a scientific magazine. Then was a trivia question in Trivial Pursuit and the rest is history...
According to the traditional meaning of Blue Moon, the next one occurs May 19, 2019 (the day before my birthday, that feels special) and then August 22, 2021. While I did my best not sound like to much of a know it all...I would love to change the Gregorian calendar consciousness to the seasons and Earth's importance in the experience of the full moon.