@PATAX  - look what I found 😉

Contrary to the popular phrase "once in a blue moon", Blue Moons can occur relatively frequently, that is, in astronomical terms. 

Blue Moons occur once every two to three years, according to NASA. As there are roughly 29.5 days between full moons, February will never experience a monthly Blue Moon as it only has 28 days in a common year and 29 in a leap year. Sometimes February doesn't have a Full Moon at all, this is known as a Black Moon, according to Time and Date.