A Blue Moon will occur on Saturday, March 31.
A Blue Moon is defined as the second full moon within a month. This happens to be the second Blue Moon of 2018. The last one occurred on January 31.
Having two in the same year is rather rare. The last time there two Blue Moons in a year was in 1999, and it won’t happen again until 2037. The next regular Blue Moon will happen on Halloween, 2020.
There is an alternate definition that states a Blue Moon is the third of fourth full moon in a season. However most people recognize the traditional definition of having two full moons in a single month.
By the way, a Blue Moon is not actually colored blue. The color of the moon is controlled by things in our atmosphere such as smoke and dust particles. While a blue-colored moon is not out of the question, it’s doubtful it would occur at the same time as the second full moon of the month.