Once in a Blue Moon

More about Once in a Blue Moon

The term "blue moon" has been used to describe different phenomena, but the most common meaning is a second full moon that occurs within a calendar month.
The term "blue moon" has nothing to do with the actual colour of the moon, and a blue-coloured moon is actually a very rare occurrence caused by atmospheric conditions such as smoke or dust particles in the air. A blue moon looks just like any other full moon.
Two of the multiple theories about the origin of the name "blue moon" are:
1. The name may have come from an old definition of "blue": In some old English texts, the word "blue" was used to mean "betrayer" or "deceitful." It's possible that the name "blue moon" came from the idea that an extra full moon in a month was deceptive or misleading
2. The phrase "once in a blue moon" has been used for centuries to describe rare events. It's possible that the term "blue moon" was later applied to the second full moon in a calendar month because it was also a rare occurrence.