A True Blue Moon

I toddled off to bed last night knowing there was a full Moon, after all, our bedroom was flooded with magical, silvery light.

What I didn’t know was, last night’s full Moon was a ‘True Blue Moon’.

–⋅ o ♥ o ⋅–

There are two different definitions for a Blue Moon.

Firstly, I’ll talk about the second definition – the Monthly Blue Moon – when a full Moon occurs for the second time during any one calendar month (except February*). This is the type of Blue Moon of which most of us are aware.

The origins of the Monthly Blue Moon owes its existence to a misinterpretation originally made by amateur astronomer James Pruett in his article “Once in a Blue Moon,” in a 1946 edition of Sky & Telescope magazine. (I have spoken about this before.) Pruett’s error took on a life of its own and the rest is, as they say, history. Although, these days, this error is now considered a second definition rather than a mistake. I like that.

–⋅ o ♥ o ⋅–

The first definition, a True Blue Moon, is a Seasonal Blue Moon. This is the third full Moon of an astronomical season that contains four full Moons. Unlike meteorological seasons that begin on the first day of the months that include the equinoxes and solstices, the beginning and end of an astronomical season is defined by the dates of equinoxes and solstices.

I’m not sure I ever really understood this, but I do now.

Our current astronomical season commenced on June 21 and ends on September 23. Here in the southern hemisphere, that’s the time between Winter solstice and Spring equinox with full Moons occurring on June 25, July 24, August 22, and September 21.

I hope I haven’t lost you 🌝

Last night’s full Moon was the third full Moon in the current astronomical season making it not only a Blue Moon but, a Blue Moon in the true sense of the meaning.

–⋅ o ♥ o ⋅–

The next Seasonal Blue Moon will take place on August 19/20, 2024.

The next Monthly Blue Moon will be a little earlier on August 30/31, 2023.

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* Sadly, as the Moon’s lunar phase takes 29.5 days to complete a cycle, February can never experience a Blue Moon, but every other month of the calendar can.