Much has been made of a Blood Moon, a reddish moon in a total eclipse…and we all know of a blue moon. But how often do you hear of it being green?
I caught the moon in one such view with a Kodak AZ251 at its maximum optical zoom (25X) during the recent total eclipse early Saturday morning. See the greenish tint in the picture above? It doesn’t appear to be a camera or low-light artifact. Another view a few minutes later, with even less light and the very same camera settings, appears correspondingly darker in the picture below.
If you look carefully enough at the very beginning of the total eclipse, as in the second picture above, you may see the rest of the moon colored a faint reddish brown. Beyond this, with a complete absence of direct sunlight shining on the moon, I did see it a brighter red, lasting for a while before direct sunlight began to shine on an edge again. My rather basic digital camera could not capture the red phase at all.
Discussing this with a friend, a professor in optoelectronics at a preeminent university in India, we think the green moon is an opportune capture near the cusp of a total lunar eclipse. Through a combination of refraction (varied bending of different light wavelengths, as in a Prism) and scattering through earth’s atmosphere, that limits the spectrum of sunlight reaching the moon, a mixing of light from the yellow to the blue wavelengths could have given us this greenish tint. This may only occur for a very short period of time before the eclipse, if at all.
It did make me wonder: could there also be a blue tint, for a fleeting moment even? But blue is a color scattered most by the atmosphere – hence the blue skies we see so often – and any such light passing through the atmosphere on to the moon is most likely quite dim… A blue moon is hence highly unlikely, making it an apt indicator for similarly unlikely expectations!
Update (Aug. 1, 2015): BBC article on a Blue Moon (the second full moon in a calendar month) around the world.