What is a Blue Moon?
The year 2018 is a Blue Moon bonanza! There was one in January and one on March 31st. The next one won’t arrive until October 2020. But, don’t worry… we’ve got 3 other types of moons lined up for you.
The Basics
A Blue Moon happens when there is a Full Moon on the 1st* day of the month and a Full Moon on the last* day of the month. Two full moons in one month!
In other words, a Blue Moon is when there is a full moon twice in the same month. These two full moons always happen on the 1st or 2nd and the 30th and 31st of a month. “Blue Moon” is just a name for the second moon in that month – the moon does not turn the color blue.
Read on to learn about how the Blue Moon came to be and some suggestions for giving the other moon phases “Blue Moon” style names when they appear twice in a month. Suggestions are: Dark Moon, Nose Moon, and Tail Moon.
A month is just a name for 30 or 31 days in a row
Month came from the word Moon. The concept of the month came from the moon phase cycle. It is not a coincidence that the month is about as long as a moon phase cycle. They are related.
The Blue Moon not a very old concept… it was invented by accident in 1946. It happens because our 12 month calendar no longer matches the moon phases.
The moon’s phases have a cycle that is 29 and a half days long. All calendar months (except February) are 30 or 31 days long. So, every once-in-a while (“once in a blue moon” you might say) the moon’s phase cycle fits inside a single calendar month.
Here’s a calendar month showing the 2 full Moons that will happen in October 2020.
Evolution of Blue Moon definition.
Today, the definition is: “A Blue Moon is the second full moon in a calendar month.” Before 1946, this was not the meaning of “Blue Moon.”
Most years have 12 full moons in the year. But, sometimes there are 13 full moons in a calendar year. In the “olden days,” it is thought that the term Blue Moon was a way of naming the “extra” 13th full moon that sometimes comes in a calendar year. This naming of the extra moon in a year was handled by calendar makers (people who picked the calendar dates for holidays like Easter and Passover). Normally, this “Blue Moon” (old style) was thought of as the 4th full moon in a season (normally only 3 full moons are in a season).
This linguist thinks it was really just a funny saying to mean something like “when pigs fly” as in “when the moon turns blue” (which according to word history research is something that people believed would never happen).
A Blue Moon that’s not a Full Moon
The blue moon refers to the full moon phase. The fact that the entire moon phase cycle fits into a 30+ day calendar month is interesting. But, it’s just a phase. And the other moon phases are arguably much more interesting.
Think about it for a second… it’s not just the full moon that can appear twice in one month. Any of the other major phases can appear twice in one calendar month. Why should the Full Moon be the only phase with a special name?
The full moon is just the most obvious and well-known phase. It is also the easiest to spot because it is so bright! However, there are 3 other major phases of the phases of the moon (new, first quarter and last quarter). Those phases can appear twice in a calendar month just like the full moon phase.
For instance, October 2018 will have two “Last Quarter” moons, one on October 2nd, 2018 and one on October 31st, 2018. This Last Quarter phase should have its own special name too. I think that we should call the 2nd last quarter moon in a month the Nose Moon.
Blue Moon extended: Dark Moon, Nose Moon, Tail Moon
Blue moons are fun to think about! It’s when the wall calendar overlaps with the physical motions of the Moon and the Sun and two full moons happen in the same calendar month.
There are also other phases the “happen twice” in a calendar month. These phases should also have names.
Blue Moon -2 Full Moons – already in widespread use, common name.
Here are new names I created to give the other moon phases some glory too:
Dark Moon – 2 New Moons – New moons are dark and cause eclipses.
Nose Moon – 2 Last quarter –the last quarter moon leads us in our orbit.
Tail Moon – 2 First quarter – this moon trails Earth by about 4 hours.
What do you think of these new names? Leave a comment below.
Summary
The simplest and shortest definition is:
Blue Moon is the second full moon in a month.
The Blue Moon used to mean something slightly different relating to the adjustments needed to keep lunar and solar calendars in synch: the 4th full moon in a normally 3 moon season.
The Full Moon phase is only one of the 4 major phases of the moon – we should have names for all moon phases when they appear twice in a calendar month.
Full = Blue Moon, New = Dark Moon, Last = Nose Moon, First = Tail Moon.
Fun Facts
February can never have a Blue Moon because it only has 28 (or 29) days and the Moon becomes full every 29.5 days.
The Blue Moon got its modern meaning because of a mistake by one of the writers in Sky & Telescope magazine in March 1946.
There are historical records that tell us that Volcano dust and forest fires can cause the Moon to appear the actual color blue.
Notes
* The first full moon can be on the 1st or the 2nd day of the month, and the last full moon can be on the second-to-last or last day of the month.