Boo Moon

No, this post is not about some Korean politician. It is about the Blue Moon that coincides with the spooooooky Halloween night this year 31 Oct 2020. A nice astronomical coincidence which happens every now and then. But then, how often? This is an interesting fun fact, so keep reading.

First, what is a Blue Moon? For more than half a century, whenever two full Moons appear in a single month (which happens on average every 2 1/2 to 3 years), the second full Moon is christened a “Blue Moon”. Of course, the name does not relate to the actual color of our faithful satellite. It seems that came up as a mistake made by some newspaper man more than half a century ago who got confused with the Full Moon about to show up in the skies. Instead he wrote “Blue Moon” in his article and boom, there comes a term used till today.

A Boo Moon is a blue Moon occuring on Halloween night, i.e. 31 Oct of some year. One can calculate when this coincidence happens using the Metonic Cycle. Meton, an ancient astronomer in Athens, Greece in 432 BC calculated that every 19 years, the lunar cycle returns back to the exact date. This of course is an approximation as we have leap years, the lunar cycle is 29.5 days and not 29 and so on. However, it seems it works ok more or less.

Our last Boo Moon was in 1944 preceded by year 1925. Then due to the approximation it leaped to Nov 1st in 1963 till it finally showed up on Oct 31st, 2020 again.

Enjoy your boos and trick or treat if you celebrate Halloween around the world. For the rest, enjoy a nice full moon in the sky till the next Boo Moon comes back in 2039 , 2058, 2077 and 2096 this century. Stay safe and howl tonight!


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