In the spring, the earthworm creeps its way up through the thawing soil, while spring’s first full moon gets ready to creep likewise—up over the horizon. It might sit lower than usual, appearing to loom larger, and even taking on a reddish glow.
In a nod to this crawler’s seasonal debut, the March full moon has been dubbed the Worm Moon. This year’s will fall on Monday, March 25, reaching peak illumination at 3:00 a.m. EST.
Worm Moon Origins
Earthworms might have been on the minds of the Colonial settlers or Native American tribesmen who bequeathed the entire calendar month (not just the full moon itself) this name. But another form of grub (not earthworms) may actually be the true originator of the moniker Full Worm Moon.
A number of other names have been given also, the Farmer’s Almanac writes, including several after animals: the Eagle Moon and Goose Moon (so-called by the Algonquin and Cree tribes) and the Crow Comes Back Moon (Northern Ojibwe).
Other names point to the season: The Sugar Moon (Ojibwe) alludes to the sap from sugar maples that starts to flow as spring begins. The Strong Wind Moon (Pueblo) denotes the coming of windy days. The Sore Eyes Moon (Dakota, Lakota, and Assiniboine) is named after the sun’s bright reflection off the melting snow.
A Colorful Moon Illusion
On 364 days of the year, the moon’s arc will be either riding ever higher into the autumn or winter sky before descending toward spring; or else falling further down, passing from spring into summer to hide behind trees and buildings, or drop out of sight below the horizon. But on the first day of spring, called the spring equinox, due to certain spatial mechanics connected to the tilt of the Earth’s axis, the moon will often seem to linger for long bouts around the horizon.
This year’s Full Worm Moon on March 25 will coincide closely with the spring equinox, which falls a few days earlier, on March 19. Thus, the moon may appear especially close to the horizon and, as a consequence, might even take on some spectacular appearances: it could appear larger than usual or assume a rust-red tinge.
The reason? It’s part optical illusion and part natural special effect.
Shades of ochre or rust-red can appear on the moon when near the horizon. The cause? It’s because a lot of sunlight that reaches the moon and illuminates its surface must pass through Earth’s atmosphere, which acts as a filter, scattering light. Colors with shorter wavelengths, blues and violets, are dispersed while colors with longer wavelengths, reds and oranges, pass through, coloring the moon. This is only enhanced by smoke in the atmosphere.
On top of this, there will also be a partial lunar eclipse during the Full Worm Moon. It will partially enter the area of Earth’s shadow where there is no sunlight, called the umbra, causing its color to deepen.
If you want to shake off those winter blues by viewing the Full Worm Moon, it will rise in the east around sunset. Although it technically falls on March 25, the full moon will seem nearly full on Sunday and Tuesday, the nights before and after. What better way is there to usher in spring?
