A rare blue supermoon is set to be visible in the night sky on the evening of August 31. A supermoon occurs when the moon is at its closest point to Earth, making it appear larger and brighter. This particular event is also a blue moon, meaning it is the second full moon in a single month. The last blue supermoon occurred in 2009, and the next one is not expected until 2037. The term "blue moon" does not refer to the color of the moon, but rather the occurrence of a second full moon in a month.