A monthly Blue Moon is the second full moon in a calendar month, which occurs once every two or three years. In 2018 there were Blue Moons in both January and March. These double Blue Moons only happen about 3 to 5 times in a century, with the next occurrence in 2037. With the lunar cycle being approximately 29.5 days February will never have a Blue Moon. (http://bit.ly/2HKANrV)