Daily Postcard: The rising of the Blue Moon is reflected in the pond at a residence Saturday night in the valley. A ‘Blue Moon’ is a fairly infrequent phenomenon involving the appearance of an additional full moon within a given period. But which period? It turns out there are two definitions of the term, and one was borne out of a misunderstanding of the other. The older meaning defines a Blue Moon as the third full moon in a season that has four full moons. Called a seasonal Blue Moon, this occurs about every 2.5 years, according to NASA. More recently, the term Blue Moon has been applied to the second full moon within a single calendar month. There are roughly 29.5 days between full moons, making it unusual for two full moons to fit into a 30- or 31-day-long month. (This means that February will never have a Blue Moon.) Source: space.com. Photo by Liddie Martinez