In September 2015, a new study provided an important missing piece to the intriguing puzzle of how our Moon came to be the lovely object that we see today.
Among the ringed gas giant planet Saturn's amazing collection of 62 diverse, bizarre, and beautiful moons and moonlets, sometimes one of them just seems to stand out in the crowd. Such a moon is little Methone. Looking like a shiny white egg in Space, and composed of very lightweight fluffy stuff, Methone is less dense than any other known moon or asteroid in our Solar System. In March 2013, astronomers announced at the 44th Lunar and Planetary Science Conference held in the Woodlands, Texas, that this strange little 5-kilometer-size moon is one of a batch of Space eggs in orbit around Saturn!
So here you have two definitions of a blue moon but the one for a calendar blue moon does not describe the true meaning of a blue moon. Here's why: