Once in a Blue Moon ?

A "Blue Moon" is a real phenomena yes! The term is used to describe when there are two full moons in a calendar month. On average there are around 40 blue moons per century so they are not overly common. This is why the saying "once in a blue moon" is a good way to describe something that doesn't happen very often!

I understand it means that once in a while. Full Moon is seen twice in a month, therefore, if you are going for any activity say once in 15-20 days, it is said that once in a blue moon. It is an idom, I suppose.

We've all heard the saying "it happens only once in a blue moon," generally used to describe an uncommon occurance. Using the phrase "once in a blue moon" could also mean "two out of three times." But like the others said above me said Blue Moon is something real. A 'blue moon' really doesn't have anything to do with color. Instead, it is the term used to denote the second full moon that occurs within a given calendar month. Because it takes the moon about 29 days to circle the Earth once in its orbit, it is possible that two full moons can occur within the same calendar month.

It means very rarely. I have seen a blue moon, It was the most beautiful and amazing thing I have evr seen in my life!

My sister told me that in a rare occasion, we can see the moon with a little blue crescent on the side. She said that it is just a shadow but it seems like a second moon overlapped by our moon. "The blue moon".