What Is the Spring Equinox?

Don’t capitalize terms like “fall equinox” and “summer solstice.”

Samantha Enslen, Writing for
3-minute read
Episode #670

Wednesday, March 20, is the spring equinox in 2019. 

And that means what, exactly?

The spring equinox is one of two days during the year when day and night are about the same length. This happens when the earth rotates in such a way that the sun is lined up exactly with the equator. In that 24-hour period, the earth’s axis is tilted neither toward the sun, nor away from it. Everyone on the planet gets the same amount of sunshine, and the same amount of dark.

Equinox = Equal + Night

The word “equinox,” as you might guess, comes from two Latin words: “aequi-,” meaning “equal,” and “noct-,” meaning “night.” 

The root word “aequi-“ can be found in lots of similar words describing things of equal balance, like “equivalent,” “equidistant,” and “equitable.” “Noct-” can be found in several words evoking night: “nocturnal”; “noctambulate,” meaning to walk around at night; and the spooky “noctifer,” an obsolete word that refers to a bringer of night or darkness.  

I’m thinking of the Dementors from “Harry Potter” when I hear that word, or the Nazgūl from “The Lord of the Rings.” Scary.

Chaucer Used the Word 'Equinox'

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We can find the word “equinox” used way back in the 1300s, when Chaucer wrote one of the first-ever technical manuals—a user’s guide to the astrolabe, an instrument that’s used to make astronomical measurements. 

Chaucer wrote of a “cercle” around the earth called the Equator. He noted that 

When the sun is at the start of Aries and Libra, the days and nights are of equal length. These signs (Aries and Libra) are called the equinoxes.

Why does Chaucer refer to these zodiac signs? Because as the Earth revolves around the sun, the sun seems to travel through all the thirteen constellations that make up the zodiac. (Really, we’re the ones moving; the sun isn’t “traveling” anywhere.) And on the day of the spring equinox, the sun looks like it’s starting to move through the constellation Aries. For that reason, the spring equinox is also called “the first point of Aries.” The fall equinox, in turn, is known as the “first point of Libra.” 

Don’t Capitalize Terms Like 'Spring Equinox' and 'Fall Equinox'

And the names of all these significant astronomical days are all lowercase. You don’t capitalize terms like “fall equinox” and “summer solstice.” The solstices, by the way, are the opposite of the equinoxes. They are the two days a year when the sun is at its most extreme position. The summer solstice is the longest day of the year and the winter solstice is the shortest day of the year.

What’s the Vernal Equinox? 

One final question: Why is the spring equinox also called the “vernal equinox?”

That’s just because “vernal” is another word for spring, derived from the Latin word “vēr,” meaning the same thing. I really wish I could say that “verdant” is also derived from this word, but it comes from a different Latin word: “viridis,” meaning green.

That just goes to show that not all words that sound the same come from the same root.

And speaking of roots, the ground should be getting soft enough for planting. Enjoy the spring equinox—and the “full worm moon,” which falls on the same day this year. Why is it called that? Because ground that’s soft enough to put plants in is soft enough to have worms come out. Hope you—and the robins—have fun. 

Samantha Enslen runs Dragonfly Editorial. You can find her at dragonflyeditorial.com or on Twitter as @DragonflyEdit.


Boeckmann, Catherine. First Day of Spring 2019: The Spring Equinox. The Old Farmer’s Almanac, February 7, 2019 (accessed March 11, 2019). 

Boeckmann, Catherine. Full Moon for March 2019. The Old Farmer’s Almanac, March 5, 2019 (accessed March 11, 2019). 

Chaucer, Geoffrey. A Treatise on the Astrolabe, p. 147. University of Oklahoma Press, 2002 (accessed March 11, 2019)

Chaucer, Geoffrey; James E. Morrison, ed. Chaucer’s Astrolabe Treatise, p. 5. Chirurgeon’s Point (accessed March 11, 2019)

Encyclopedia Britannica, online edition. Equinox (subscription required, accessed March 11, 2019).

Oxford English Dictionary. Equinox, nocturnal, verdant (subscription required, accessed March 11, 2019).

National Geographic. Video: What is an Equinox? September 22, 2017 (accessed March 11, 2019). 

National Weather Service. The Seasons, The Equinox, and the Solstices (accessed March 11, 2019). 

Image courtesy of Shutterstock.

About the Author

Samantha Enslen, Writing for Grammar Girl

Samantha Enslen is an award-winning writer who has worked in publishing for more than 20 years. She runs Dragonfly Editorial, an agency that provides copywriting, editing, and design for scientific, medical, technical, and corporate materials. Sam is the vice president of ACES, The Society for Editing, and is the managing editor of Tracking Changes, ACES' quarterly journal.