When someone says that they do something once in a blue moon, it generally means that they don’t do it very often, but where does that term come from?

It has a long history dating back to the 16th century, when the phrase “The Moon is Blue” was applied to something that was impossible. Over time, the usage of the phrase evolved until what we hear today, “Once in a Blue Moon,” doesn’t mean that something is impossible, but just that it is rare.

As with almost all words and phrases, the change took place over time. One key moment was in the 1937 edition of the Maine Farmer’s Almanac, where the names of full moons were first codified. In this edition, a blue moon was the third full moon in a season where there are four full moons.

The second definition came from a 1946 edition of the American magazine, “Sky and Telescope.” In this magazine, the author misunderstood what the Farmer’s Almanac meant and incorrectly said that a blue moon was the second full moon in any month.

Interestingly, that second definition, which was just a misunderstanding, actually caught on very well and has now become the standard meaning.

Based on either of these astronomical definitions, a blue moon occurs about once every year or every other year, which indeed is pretty rare, but far from unheard of.

If you’re someone who loves unusual lunar events like this, you should really be looking forward to 2028. In that year, on December 31st, there will be a blue moon. That full moon will also be a super moon, which is when the moon is at its closest point to Earth, so it looks larger.

On top of that, it will occur during a total lunar eclipse, which means it will turn a reddish color known as a blood moon.

When that happens, you could call it a super blood blue moon, which truly is a very rare event indeed.

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