RICHMOND, Va. (WTVR) - Tuesday night's moon rises at 7:27 p.m. and goes full at 9:45 p.m..
It isn't the second full moon of the month, but it is called the Blue Moon, among many other names, because of an obscure rule.
It's also called the Full Sturgeon Moon, the Full Red Moon, the Green Corn Moon and the Grain Moon.
This month's full moon is considered a Blue Moon because it's the third full moon in a season with four (most seasons have only three) full moons. So how do you define a season? It's the days in between a solstice and equinox: in this case, the time between the Summer Solstice on June 21, 2013 to the Autumnal Equinox on September 22, 2013. And we just edge in an "extra" Full Moon to the Summer season line-up in that time-frame.
After Tuesday's event, the next Blue Moon isn't set to occur until 2015.
Bruce McClure and Deborah Byrd of EarthSky explain how often this type of Blue Moon occurs. "So how often do we have a Blue Moon by the seasonal definition – the third of four full moons in one season? In a period of 19 years, there are 235 full moons but only 228 calendar months (76 three-month seasons). Given that there are 76 seasons and 235 full moons in 19 calendar years, it’s inevitable that at 7 of these 76 seasons should harbor four full moons. In other words, if you’re defining a Blue Moon as the third of four full moons in the same season, you’ll have a Blue Moon once every two to three years."
For the full back story on how the term "Blue Moon" gained two meanings, click over here to SPACE.com.
In more lunar history, the annual August full moon is known as the Full Sturgeon Moon, because the sturgeon can most easily be caught at this time of year.
This month's moon is sometimes called the Green Corn Moon or the Grain Moon because crops grow tall at this time of year. The farmer's almanac reports that it was known by a few tribes as the Full Red Moon because, as the Moon rises, it appears reddish through any sultry haze.