If you happened to look at the moon Friday night, you may have noticed it was full. If you have a really good memory, you will know there was also a full moon to start the month. That means that Friday night's moon was a blue moon.
The moon wasn't actually blue -- it just means that the full moon appeared twice in the same calendar month.
Check out the video to see a time-lapse of the moon as it appeared about the U.S. Capitol.
There will not be another blue moon until 2018.