By Terry Eliasen, Meteorologist, WBZ-TV Exec. Weather Producer

BOSTON (CBS) – Once in a Blue Moon … again?

Getting a case of deja’vu? Does it seem like we were just talking about the rather rare “Blue Moon?” Well we were! This weekend we will have our second Blue Moon of 2018! How can this be? What is happening? Well, I’m glad you asked.

When the moon is officially full Saturday morning at 8:37 a.m., it will indeed be our second full moon in the month of March, hence the term “Blue Moon.” A Blue Moon occurs roughly about once every 2.66 years, yet this is our second in the last three months.

2017nightsky2 Weekend Blue Moon Sighting Will Be Second Of 2018

(WBZ-TV Graphic)

You may remember we also had two full moons in the month of January. What’s even odder, we had ZERO full moons in February AND we won’t have another Blue Moon until 2020! So what’s the deal?

Here is where you can bring some serious knowledge to the Easter Dinner table and amaze your family.

A moon cycle lasts 29.53 days (otherwise known as a “synodic” month), obviously less than a full calendar month, unless of course you are talking about February. So once in a while, you get the stars (or moon) to align just right and you get two full moons in January and two in March with nothing in February. This occurs once every “Metonic Cylce.” Another new vocab word!

2017nightsky3 Weekend Blue Moon Sighting Will Be Second Of 2018

(WBZ-TV Graphic)

The Metonic Cycle is precisely 235 lunar months, or 19 years long, after which the full moons return to just about the same dates. So therefore we know that 19 years from now, in 2037 we will, once again, have the same double Blue Moon as we did this year. Science is cool!

You want one more moon fun-fact? Why not! This weekend’s Blue Moon will also be a “Paschal Moon”.  This is the definition of the first full moon of spring. And with spring beginning just a little over a week ago, we can check that box as well.

Want to check it out?

Friday Moonrise: 6:18 p.m.
Saturday Moonrise: 7:25 p.m.
Sunday Moonrise: 8:31 p.m.

Follow Terry on Twitter @TerryWBZ

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