Blue Moon one day late. It was cloudy the night of Dec. 31, so I took this on Jan. 1, 2010. Tonight, December 31, 2009, we will have a blue moon. Does that mean it will look blue? Not really. “Blue Moon” is an expression that we use whenever we have a second full moon in a month. What is a full moon? A full moon happens when the sun and moon are on the opposite sides of the earth so the sun lights up every