Space is theater. Perhaps the most dramatic spectacles human beings will ever observe are the result of the eternal dance among the cosmos’s moons, planets, stars, and more. A close-to-home sky show will be put on late in the evening of Thursday, March 13 and into the early morning hours of March 14. This is when a so-called “blood moon” lunar eclipse plays out, visible in North and South America, parts of Africa, the Pacific, and Europe. So what causes a lunar eclipse, when is the best time to view this one—and how did it get that striking blood moon moniker?
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As the moon orbits the Earth and the Earth orbits the sun, the three bodies are forever getting in one another’s way, periodically blocking the view from one to the other. When the moon passes between the sun and the Earth, as happened last April 8, a solar eclipse occurs, with the disk of the moon blocking the disk of the sun, casting a shadow on our planet. The moon is 400 times smaller than the sun, meaning it should not have much of an effect on how much sunlight reaches us. But in a wonderful bit of cosmic serendipity, the moon is also 400 times closer to us, which results in the solar and lunar disks appearing to be exactly the same size in our sky, making for a perfect fit, with only the sun’s corona—or fires—flaring out from behind the moon during totality.
Lunar eclipses rely on a different sun-moon-Earth lineup, occurring when the Earth moves between the sun and the moon, blocking the solar light that typically reflects off the lunar surface and casting a shadow in its place. Lunar eclipses can either be partial, with only some of the moon’s surface covered, or total, with the entire face of the moon darkened. The type of lunar eclipse depends on how precise the alignment of the three bodies is.
The moon does not orbit the Earth in a perfectly flat plane around our planet’s equator. Rather, its orbit is slightly cockeyed, tilted at an angle of 5.145 degrees. That means that sometimes the moon will pass in front of the Earth slightly above or below the planet’s midline, allowing some solar light to reach a portion of the lunar surface. Only when the three bodies are perfectly lined up—as they will be this week—will a total lunar eclipse occur.
Unlike a total solar eclipse, when the disk of the sun is completely blackened, an eclipsed moon does not vanish completely from the sky. Rather it is still bathed in some sunlight streaming past the Earth and, significantly, through its atmosphere. That has a dramatic effect on the color of the moon. Solar light contains all of the colors of the visible spectrum, but as it reaches our atmosphere, the higher frequency blue wavelengths are scattered out—which is what gives our sky its characteristic color. Red and orange wavelengths pass right through. In the case of a lunar eclipse, that means the moon is bathed in a reddish glow—hence the blood moon handle.
There are other names for a full moon at this time of year when a lunar eclipse is not taking place. According to the Old Farmer’s Almanac, a March full moon is also called a worm moon—a name attributed to the earthworms that typically emerge from the ground in early spring, or to the beetle larvae that also emerge from the branches of trees in the post-winter thaw. Indigenous American tribes have also dubbed the March full moon the Eagle Moon, the Goose Moon, or the Crow Comes Back Moon, heralding the reappearance of these animals in the Spring.
Whatever name the moon goes by, watching it fall into shadow this week will likely cause you to lose some sleep. According to NASA, the moon will first begin to move into shadow at 11:57 p.m. EDT (8:57 p.m. PDT) on March 13. Totality begins at 2:26 a.m. on March 14 on the east coast (11:26 p.m. on March 13 out west) and lasts just over an hour. If you sleep through this one, you’ll get other chances. About two lunar eclipses occur each year on average. The next one will happen on Sept. 7, 2025—though it will give the Americas a pass, while being visible over most of the rest of the world. The next lunar eclipse to bathe our continent will play out on June 26, 2029. The nighttime sky will, as is its wont, continue to put on its pageants.
