Today (January 31), with popular terms, there was a “super blue blood moon”. It will be the first full total moon eclipse since September 27/28, 2015. What’s more, it was the first Blue Moon / Blood Moon visible from the United States since 1866.
UPDATE: NASA is live now, saying “We’re live online with views of the #SuperBlueBloodMoon from @UHawaiiNews.” (Click here to watch the live stream)
What is a Blue Moon?
The phrase has nothing to do with the actual color of the moon. A blue moon is an additional full moon that appears in a subdivision of a year: either the third of four full moons in a season, or a second full moon in a month of the common calendar.
A literal “blue moon” (the moon appearing with a tinge of blue) may occur in certain atmospheric conditions: e.g., if volcanic eruptions or fires leave particles in the atmosphere of just the right size to preferentially scatter red light. But it’s completely a different phenomenon than “blue moon”.
What is a Blood Moon?
Like Super Moon, Blood Moon is not a scientific term. In recent times it is being widely used to refer to a total lunar eclipse because a fully eclipsed Moon often takes on a reddish color. See the NASA image below, when the moon passes through Earth’s extended shadow, the penumbra, it looks reddish. When it passes through Earth’s central shadow, the umbra, it’s naturally black and that is the eclipse.