Saturday’s Blue Flower Moon

| May 14, 2019 @ 8:26 am

The moon turns full again this Saturday, it’s May so many call it the flower moon, but you could also call it the blue flower moon.

The term blue moon most often, at least recently, refers to the 2nd full moon in a calendar month. This happens about every 2.4 years. Since it takes about 29.5 days for the moon to go from full through new and back to full again, or the lunation period, this calendrical coincidence only happens on the 30th or 31st day of the month.

But Saturday is the 18th, so how can it be blue? That’s not the only definition of a blue moon.

This monthly definition originated in a 1946 article in Sky and Telescope and appears to be a misinterpretation of the original definition which dates back to the 1937 edition Farmers’ Almanac, a more seasonal definition.

Saturday’s is the third of four full moons this spring. Seasonal blue moons occur every 2.68 years on average. Why the third and not the fourth? No one seems to know. This is the Farmers Almanac not The Astrophysical Journal after all

The last seasonal blue moon occurred May 21, 2016, the next occurs August 8, 2021
The last monthly blue moon occurred March 31, 2019, next occurs Halloween 2020

Category: ALL POSTS, Spacey Stuff

About the Author ()

Tony Rice is a NASA/JPL Solar System Ambassador and the voice and brains behinds the weekly Astronomy Report on the WeatherBrains podcast. He grew up in Southern California where he watched the Space Shuttles being build and landed nearby and was hooked. Tony brings weather and space together to communicate the excitement of space exploration and promote a greater appreciation for Earth sciences.

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