A rare blue moon will light up on the night sky on October 31 this year. That's the second full moon in a month.
According to NASA, it only happens about every three years.
October's first full moon will appear on the first day of the month.
The second full moon then - the blue moon - will be on Halloween.
But, heads up, the moon won't actually look blue. It'll be the same color it's always been.