If you happen to look up in the sky on Friday, you'll see something that only occurs "once in a blue moon."
That's because it'll be a blue moon, the second full moon of the month, but this wasn't always the definition of the blue moon. Watch the video to find out more:
Just because it's called a blue moon doesn't necessarily mean the moon will appear blue.
The moon only appears blue when smoke or dust particles are in the atmosphere, usually from a volcanic eruption or large wildfire.
The last time we saw one of these rare events was August 31, 2012, and the next time one will be visible in the United States will be January 31, 2018.