A rare Blue Moon in the sky

DENVER - This month's full moon, is not just a "Blue Moon" -- it's also the Full Sturgeon Moon, the Full Red Moon, the Green Corn Moon and the Grain Moon.

Tuesday night's full moon qualifies as a Blue Moon because it's the third full moon in a season with four (most seasons have only three). Historically, there have been two different definitions for a Blue Moon.  It will also be a Red Moon and a Sturgeon Moon!

It's the last Blue Moon we'll see until 2015 -- and will be visible until Wednesday morning.

In astronomy, a BLUE MOON is actually defined as the third full moon in a four-full-moon season. We will have four full moons in this summer season as we had a full moon just after the beginning of summer, one in July, the current full moon and one more next month, just before autumn begins.

The commonly believed definition of a Blue Moon being the second full moon in a calendar month comes from an article in "Sky & Telescope" magazine way back in 1946!  That article mistakenly defined it as the second full moon in a single month (since most months have only one full moon), and that definition gained traction and is still widely held to this day.

Because August will have just this one full moon, it would not meet the mistaken, though commonly used, definition for a Blue Moon.

The moon's extra names come from various lore over the past 300 years. Native American tribes in what's now the northeastern United States kept track of seasons by ascribing particular names to each full moon. Later, European settlers added their own names for the full moons to the lexicon.

The term Red Moon comes from the fact that late summer forest fires often send a great deal of smoke into the atmosphere.  The smoke particles filter out the shorter (blue) wavelengths of light, leaving the moon with a reddish appearance.

The Grain Moon and Corn Moon names are believed to be from the early settlers who would plant by the calendar and -- by this time of year -- the grain and corn would be tall in the fields, not quite ready for the harvest -- which comes with the next full moon!

The annual August full moon has also come to be known as the Full Sturgeon Moon, because the large fish called sturgeon can most easily be caught at this time of year. The name came from tribes who caught this fish in bodies of water such as the Great Lakes and Lake Champlain.