Ever heard that old phrase “once in a blue moon?”  But what is a blue moon, really? Contrary to popular belief, a blue moon is not a full moon that appears to have a soft bluish-white glow.  People have been using the phrase ‘once in a blue moon’ since the 1800s to describe something that rarely happens, such as the moon appearing to be colored blue, but this was not always the case and isn’t the most likely source of the...