A little ramble through the night sky - the Micro Blue Moon on May 31st.

It’s May Moon Madness this month, as there are two full moons,  meaning the second one is a Blue Moon, and in addition, both are Micro Moons. The last time this happened was in October 2020 and the next will be in July 2053.

There will be two full moons this month, one on the first and the other on the thirty-first. This second one is referred to nowadays as a ‘Blue Moon’. The Moon takes around twenty-nine and a half days to orbit the Earth once and apart from February all months have either thirty or thirty-one days, meaning it is possible to have two full moons in a calendar month.

This use of the term ‘blue moon’ only has a history dating back to the 1940s when a letter, sent to the American astronomy magazine ‘Sky and Telescope’ (which incidentally is still published) asked the question ‘what is a blue moon?’. The answer was that it is the second full moon in a calendar month. The publishers of the magazine, realising that they had given the wrong answer, retracted their original statement. However, it was too late; the genie was out of the bottle, and for the last eighty years everyone has accepted this definition.

I have my own theory about the term ‘blue moon’. Each month I give the name of the next full moon, and as I often say, these names go back to the times of the monastic period in Britain around 1,000 years ago. The monks, who were amongst the cleverest people around during the Middle Ages due to their vast monastic libraries, knew full well that in some years there were thirteen full moons, rather the normal twelve.

Monks liked order in their lives. They kept diaries and special dates were always marked in red ink. The phrase ‘a red letter day’ is a monastic saying going back over 1,000 years. I just wonder if, when this 13th full moon occurred, it was marked in diaries in blue ink as a source of irritation because it messed up a very orderly system. I once checked the reference library in York minster without success, but maybe someone in the future will check the Vatican library and discover a monk’s diary with a full moon marked in blue ink!

You have probably heard of the Super Moon, but did you know we also have the Micro Moon?

The Moon takes around one month to orbit the Earth. Its normal distance from us is 239,000 miles.  A micro moon occurs when the Moon is more than 250,000 miles away. A supermoon is when the Moon is less than 230,000 miles away.  This is why a supermoon appears larger than normal, while a micromoon appears smaller. The discrepancy happens because the Moon does not orbit the Earth in a circle but in an ellipse or egg shape.

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