Blue moon: The lunar phenomenon actually has nothing to do with the color of the moon, but rather, the term describes the unusual phase of a second full moon in a solar calendar month. Tuesday night’s blue moon is the last we’ll see until 2015, reports USA Today on Aug. 20.
While a full moon can occasionally take on a reddish hue, this week’s blue moon is not reflecting any color. There have been actual “blue” moons however. Particulates in the air from a forest fire or a volcanic eruption reaching the upper atmosphere can make the moon appear to take on a decidedly blue tone, such as the 1991 eruption of Mount Pinatubo.
The blue moon carries many different monikers –Full Sturgeon Moon, the Green Corn Moon, the Grain Moon and the Full Red Moon. The moon may appear “full” both a day prior and a day after its full stage, but technically it only turns full at a precise moment. Last night it was at 9:45 EDT.
Why does the moon frequently appear red at times? The National Oceanic and Atmospheric Administration says that when the moon is highest in the sky, it will almost always appear a brilliant white, because the moon is seen through the least amount of atmospheric particles, such as air molecules, water vapor and pollutants.
When the moon is lower on the horizon, blue light in the spectrum is scattered first by the abundance of particles we are looking through, leaving the moon with an eerie red or orange color.
With another blue moon not coming for a number of years, the “once in a blue moon” idiom clearly applies.