Astronomers rarely use the term “Blood Moon.” When they do, they are usually using it as an alternate name for the Hunter’s Moon, the full moon that follows the Harvest Moon, usually in late October. Why? The Hunter’s Moon, like the Harvest Moon, rises slowly on autumn evenings so that it shines through a thick layer of the Earth’s atmosphere, and is colored red by what those who study the atmosphere call Raleigh scattering as well as smog and air pollution.
Changes of Color During A Lunar Eclipse
During a lunar eclipse, the Moon can sometimes turn red. The light reaching the Moon resembles the “color of blood,” but there is no way of predicting this in advance. So there are no grounds to call any particular lunar eclipse a “blood Moon” until it actually shows its color. But when it does occur, the explanation is simple:
“During a total lunar eclipse, white sunlight hitting the atmosphere on the sides of the Earth gets absorbed and then radiated out (scattered). Blue-colored light is most affected,” NASA officials wrote online. “That is, the atmosphere filters out (scatters away) most of the blue-colored light. What’s left over is the orange- and red-colored light.”
So a Moon turning red is nothing to fear. The only thing that happens during a lunar eclipse is that the Moon spends a couple of hours passing through the Earth’s shadow, hardly something to be concerned about.
Is The World Ending?
While we now have a clear understanding of much of what’s going on in the sky, people once routinely believed that astronomical events such as eclipses and comets were harbingers of disaster and doom.
Jeff Gaherty, author of Four Blood Moons: Something is About to Change writes, “When the mechanisms behind eclipses were less well understood, they were thought to be omens of bad tidings, just as comets were. Now people know that these are just normal events in the clockwork of the solar system, things which have occurred regularly for thousands of years and which will occur for thousands of years into the future.”
“Associations between ‘disastrous’ events and normal astronomical events are all fabrications of the human mind, as people attempt to find explanations for why disasters affect them. Because of the Internet and cable news channels, people now hear reports of disasters from around the world, including earthquakes, tsunamis and volcanic eruptions, which they never would have been aware of in the past.”
So, my advice to all of you who are blessed with clear skies on a night of a lunar eclipse is, don’t sweat it! This is a beautiful, natural and predictable phenomenon for all of us to see and enjoy. And since we like making predictions here at the Farmers’ Almanac, I’ll go out on a limb and state that, after the the lunar eclipse, we all will still be here.
Joe Rao is an esteemed astronomer who writes for Space.com, Sky & Telescope, and Natural History Magazine. Mr. Rao is a regular contributor to the Farmers' Almanac and serves as an associate lecturer for the Hayden Planetarium in New York City.