CNN) -- It happens only once in a blue moon -- and scientists say a blue moon is exactly what we'll see in the skies this New Year's Eve.
Don't expect an azure glow over our lunar satellite, however. The term "blue moon" simply refers to the second full moon in a calendar month, something that hasn't happened on a New Year's Eve for nearly 20 years, NASA says.
"But a blue moon on December 31 is rare.
Elvis Presley crooned about it
when he struck a hopeful tone in , singing about his love returning to his arms "When My Blue Moon Turns to Gold Again."
