Not a lot of people know that

Well, I didn't

According to my friendly online horoscope provider:

We celebrate two Full Moons this July, and when that happens in any calendar month — which is pretty rare — the second one is called the "Blue Moon." Even though the Moon does not really change colors, the image of a Blue Moon has inspired poets, songwriters... and lovers!

I've stored that one away mentally, to drop heavily into conversation at an appropriate moment.