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Blue moon: What is it and is it really blue?

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While a blue moon may appear blue for unrelated reasons, the term actually refers to the second full moon in a calendar month. (AP Photo/Michael Probst)

You've heard the phrase "blue moon" thrown around, but what does it really mean?

It actually refers to the second full moon in a calendar month, which generally occurs once every few years.

Despite the name that suggests otherwise, a blue moon is rarely the color blue. In rare and unrelated circumstances, dust or smoke particles in the atmosphere can make the moon appear blue, according to AccuWeather.
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