You probably use the idiom “once in a blue moon” to describe something that happens only rarely. You might have even hummed along with the song “Blue Moon” by Billie Holiday or taken a sip of the Belgian-style beer called “Blue Moon.” We hear about this mysterious blue moon all the time, but do we even understand what it really is? Luckily, the meaning of a blue moon does not disappoint; it’s just as enchanting as it sounds.
There are several definitions of a blue moon, but the most commonly known one is a second full moon that occurs during one calendrical month in the year. On average, this cosmically coincidental event happens roughly every 2.7 years, so it’s not exactly what I’d call “common,” but it’s certainly not so rare that we won’t experience several of them during our lifetime. And we’ve got one coming up on Jan. 31, 2018. We’re actually getting spoiled with blue moons this year since another one is expected to happen March 2018.
Not only will Jan 31. be a blue moon, but it’ll also a blood moon and a super moon. Talk about a trinity of spacial glory! To have all three lunar phenomenons happening at once is something to behold and it’ll be the first super blue blood moon in 150 years. Now THAT’S what I call “once in a blue moon!”
Now, you’re probably wondering if the moon will actually appear blue when it rises in the sky. That’s the real question, am I right? Unfortunately, the color “blue” has nothing to do with this event in outer space and a blue moon typically looks like any other full moon — big, bright, and beautiful but usually, not so blue.
That’s not to say a literal blue moon is impossible to see. In fact, during the 1800s, there was a time in which blue moons were appearing all the time, according to Romper. Can we get a time machine, anyone? In 1883, the eruption of the Indonesian volcano “Krakatoa” caused sunsets to be tinged with a greenish color and the moon to be flushed in blue. Apparently, natural disaster caused a color shift in the sky that could be seen halfway across the world. This doesn’t mean the moon turned blue in and of itself. The ash and abnormal particles in the sky merely caused a chemical reaction in the atmosphere that created the bizarre expression of color.
This also occurred on September 24, 1950, when a forest fire tore its way through Canada and the ash that filled the sky caused people from as far away as Britain to notice that the moon looked a little bluer than usual.
Much to my surprise, the blue moon on Jan. 31 will have no astrological significance (however, the blood moon most certainly will!) This is because on Jan 31., the blue moon will be calendrical rather than astrological, which is an important distinction that astrologers make. While a calendrical blue moon occurs a second time in one month, an astrological blue moon is one that occurs a second time during one solar month, that is, the period of time in which the sun passes through a zodiac sign. The next astrological blue moon won’t occur until Apr. 19, 2019, but when that happens, it’ll be a magical night.