Once in a Blue Moon, Twice in a Month

Hey hey! It’s a blue moon today!  For all those people who have used the phrase ‘Once in a blue moon,’ it finally happened.  Turns out that phrase means ‘about once every 2-3 years.’  A blue moon doesn’t mean the moon is changing colour anytime soon, just like a supermoon doesn’t mean the moon actually gains superpowers or gets noticeably bigger.  A blue moon is simply the second full moon in a calendar month.

A normal moon with a blue filter. Credit: thewhitegoddess.co.uk

The moon orbits the Earth in approximately 29.5 days.  This was how months were originally formed.  But 12 months x 29.5 days means that we are a few days short of the 365 days of the year.  Wanting them to balance out, we altered the months a bit and made most of them a bit longer (wtf February?).  So the full moon can happen any time during the month.  With the 1.5-2.5 day gap between the length of the month and the lunar cycle, we end up with two full moons in a calendar month approximately once every three years.

The blue moon isn’t like clockwork though.  In 2018 we will see a blue moon in January and in March.  Two in a three month period? All due to that weird February being a short month.  Even though we can predict exactly when all of these weird lunar phenomenon will happen, there are very loose patterns to blue moons, supermoons (moon at perigee), and lunar eclipses.  At least now we understand what is really happening and we don’t let the moon predict our lives like ancient pagans.

Well most of us get it…..

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