We Say 'Once in a Blue Moon' But Blue Moons Aren't That Rare

If something happens on a rare occasion, you might have heard someone describe is as a "once in a blue moon" situation. The phrase describes occurrences that don't come around often, making them extraordinary.

'Once in a Blue Moon' Meaning

"Once in a blue moon" means something happens only rarely, as if it's so uncommon you might not see it again for a long time. This phrase can describe activities, events or habits that don't happen frequently.

For example, if someone says, "He'd protect his family once in a blue moon," they're saying he rarely takes on that role. Or if someone only plays a game now and then, you could say they play it once in a blue moon.

Origins of the Phrase

The origins of "once in a blue moon" connect to the lunar cycles and a particular kind of full moon. Typically, each calendar month has one full moon, but every so often — about once every two or three years — a second full moon appears within a single month.

This second full moon is a “blue moon.” However, it's important to note the moon doesn't actually turn the color blue.

There are some theories that English speakers might have used the term "blue moon" to describe something so unusual it seemed almost supernatural or contrary to nature.

Is a Blue Moon the Rarest Moon?

A blue moon is not the rarest moon. A blue moon makes an appearance every two or three years, but a super blue moon is even rarer. A super blue moon is a cross between a blue moon, which happens when there are two full moons in a month, and a supermoon, when the moon appears larger than it usually does.

According to NASA, "The combination of these two special full moons, making for a 'super blue moon,' occurs about every 10 years, on average — though the time between any two occurrences can vary from two months to two decades or more."

Examples of 'Once in a Blue Moon' in Everyday Conversation

You'll hear "once in a blue moon" in all kinds of situations where people want to emphasize just how rare something is. Here are some examples.

• Social life: "They can't stand each other, but once in a blue moon, they find common ground." Here, the phrase emphasizes that two people typically do not see eye to eye, but on very rare occasions, they do.

• Work habits: "She takes a day off once in a blue moon, so we're all shocked when she actually did in January and February." This suggests she rarely takes a break, making it a big deal when she does.

• Family gatherings: "My uncle visits only once in a blue moon; otherwise, he's hard to find." This example shows how you can use the phrase to explain someone's infrequent appearances within a family.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.

Original article: We Say 'Once in a Blue Moon' But Blue Moons Aren't That Rare

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