Tonight is not only New Year's Eve, it is also a full moon tonight, in fact, it's a Blue Moon. Huh? Never seen the moon turn blue? You're right, you haven't seen it blue but you have seen a Blue Moon whether you know it or not. A Blue Moon is the second full moon in a calendar month. A full moon occurs every 29.5 days, which means there are usually 12 full moons per year. About every 2-1/2 years, an extra full moon falls within a calendar month — a Blue Moon. Our last Blue Moon was in May 2007. A Blue Moon on New Year's is quite rare, occurring every 19 years. The last time was in 1990; the next one won't come again until 2028. So if you're howling at the moon tonight, you have an excuse, especially if you only howl once in a Blue Moon.