Blue Moon Origin: The Translation Error Behind the Name 2026

The term blue moon has a fascinating origin that stems from a translation error, not from the color of our satellite. Despite the abundance of information debunking the idea of colored moons, misconceptions persist. For instance, last April, many people looked to the sky hoping to see the famous pink moon turn a strawberry hue—only to be disappointed. Now, we hear everywhere that May will bring a blue moon. This is a real term, but the moon won't actually be blue.

The blue moon of May will occur on the 31st. It's a beautiful moment to look at the sky, but simply because a full moon is always a spectacle—not because it's visibly special. In reality, the term 'blue moon' refers to an extra moon. The Moon orbits Earth every 29.5 days, so we typically have 12 full moons in a year, one each month. However, because this doesn't perfectly align with the 30 or 31 days of a month (or fewer in February), occasionally two full moons fall in the same month. That extra moon is what we call a blue moon.

Similarly, with seasons, the same thing happens. Normally there are three full moons per season. But since the solar and lunar calendars don't match exactly, sometimes a fourth full moon occurs in a season—also called a blue moon. But where does the name come from? The origin is murky, but one popular theory traces it back to a translation error. In Old English, the term 'blue moon' might have been a misinterpretation of 'belewe moon,' where 'belewe' means 'betrayer.' A betrayer moon was an extra full moon that 'betrayed' the usual count, and over time, 'belewe' evolved into 'blue.'

What Is a Blue Moon?

A blue moon is simply an additional full moon that doesn't fit the usual pattern. There are two definitions: a monthly blue moon (the second full moon in a calendar month) and a seasonal blue moon (the third full moon in a season with four full moons). The monthly definition gained popularity after a 1946 article in Sky & Telescope magazine, which mistakenly interpreted the Maine Farmers' Almanac. The seasonal definition is older and more traditional. The longer history behind the story is traced in Blue Moon Origin: The Translation Error Behind the Name.

The Translation Error That Named the Blue Moon

The most intriguing explanation for the name 'blue moon' comes from a linguistic mix-up. According to some sources, the term may have originated from the Old English word 'belewe,' meaning 'to betray.' A 'belewe moon' was an extra full moon that betrayed the expected number of moons in a season. When translated or misheard, 'belewe' could have become 'blue.' This theory, while not universally accepted, highlights how language evolves and shapes our understanding of natural phenomena. The background to this story is set out in The Real 'Place in La Mancha' Behind Don Quixote Finally Has a Name. A related thread runs through Science: latest articles. Earlier coverage in China's Lunar Robot: A 100kg Builder for Moon Base Construction shows how the argument developed.

Why the Moon Won't Actually Be Blue

Despite the name, a blue moon has nothing to do with color. The Moon's color can appear slightly blue under rare atmospheric conditions, such as after a volcanic eruption or forest fires, when particles in the atmosphere scatter red light and let blue light through. But these events are unrelated to the calendrical blue moon. So, when you hear about a blue moon, don't expect a cerulean orb—it's just a regular full moon with a quirky name. A closer look at the same subject appears in Apollo Lunar Samples: Cockroaches, Guppies and Space Sex. Anyone following the wider picture can start with Blue Origin's Lunar Mockup at NASA: A Step SpaceX Hasn't Taken. The same theme surfaces in Spotify Outage: Streaming Giant Down, Then Back Online, which takes a different angle.

When to See the Next Blue Moon

The next blue moon will occur on May 31. This is a monthly blue moon, as it's the second full moon in May. The previous one was on March 31, 2018, and the next seasonal blue moon will be on August 22, 2021. These events are relatively rare, happening every two to three years on average, which is why the phrase 'once in a blue moon' exists to describe something uncommon. Context on how this played out before sits in What Japanese Name Means Moonlight? 399+ Beautiful Girl Names. A companion piece, What Japanese Name Means Moonlight: 315+ Names for 2026 — Explained, approaches the same subject from another angle.

Key Takeaways

• Blue moon refers to an extra full moon, not a color change.
• The term may have originated from a translation error: 'belewe' (betrayer) became 'blue.'
• There are two types: monthly (second full moon in a month) and seasonal (fourth full moon in a season).
• The Moon only appears blue under specific atmospheric conditions, unrelated to the calendrical event.
• The next blue moon is on May 31, a monthly blue moon.

Blue Moon Types Comparison