(CNN) – May’s full moon is typically known as the flower moon because of all the blooms this month. This year it coincides with a rare occurrence: a blue moon.
A blue moon is the second of two full moons in a month — but it can also be the third of four full moons during a single season. In this case, it’s the third of four full moons this spring. These don’t occur as often as two full moons in a month.
This is the last seasonal blue moon until August 2021.
Very rarely, both types of blue moons happen in one year; this will occur in 2048, including a monthly blue moon in January and a seasonal one in August.
Sometimes, the moon can actually appear blue during certain sky conditions, but it can’t be predicted.