What is a blue moon? A blue moon is a full moon that hits twice in a calendar month.

Given the cycle from full moon to full moon is about 29.5 days and months are generally 30 or 31 days a full moon appearing twice in a month doesn’t happen very often. And February never has a blue moon.

I like this definition, but it is apparently a modification of the original definition which is a little more complicated. The original blue moon definition is explained like this. Given the 29.5 day cycle, most seasons of 3 months have 3 full moons. But every now and then, a season would come by, like Sep, Oct, Nov in the sketch, where there would be 4 full moons. The 3rd of these was known as a blue moon, or a seasonal blue moon. See why I like the modern definition?

Here’s a good article that explains the subtleties and history of blue moons.

Check out more moon or astronomy explanations

What is a blue moon?

Crossmodal perception is when senses interact in sometimes surprising ways. Some fun examples:

Coffee tastes better when you don’t have a loud coffee machine near you, and it also tastes more intense and less sweet if the mug is white.

In the atmosphere of a pressurised cabin when flying, with decreased humidity and air pressure and significant background noise, things taste less sweet or salty.

If you can’t hear the crunch of, say, a Pringles potato chip, then it tastes less fresh.

You might enjoy Nicola Twilley’s super New Yorker article, The Illusion of Taste, which has more of the science and plenty more examples.

Crossmodal perception

This is surely at least part of the reason that “software is eating the world.”

But I’m sure coffee will stick around for a bit too.

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Rival and non-rival goods