A blue moon is a rare event wherein a second full moon falls within a month of the common calendar. The presence of a blue moon within the calendar year results in thirteen full moons instead of twelve full moons. A more rare phenomenon is two blue moons within the same year which is said to occur every nineteen years. Over the next twenty years, we can expect to have fifteen more blue moons. The expression “once in a blue moon” refers to this rare occurrence though on even more exceptional occasions, the blue moon has in fact been blue in color. Is there a special significance to a blue moon? According to astronomy there is no special meaning, but astrologically the full moon affects us as much as it impacts the changing tides. Thus, a second blue moon may add some extra punch to the moon’s influence. At the very least, a blue moon event keeps us on our toes regarding nature’s unpredictable patterns to throw in an extra moon here and there.