The vernal equinox takes place in March each year and signals the start of spring in the Northern Hemisphere. During the vernal or spring equinox, the amount of daylight and darkness is nearly the same in length. (The word equinox comes from the Latin “aequus,” meaning equal, and “nox,” meaning night.)
In 2025, the vernal equinox takes place on March 20, signaling the start of spring in the Northern Hemisphere (and fall in the Southern Hemisphere). The Earth tilts at an angle of 23.5 degrees on its axis relative to its plane of orbit around the sun. As the Earth orbits the sun over the course of a year, different places get sunlight for different amounts of time.
An equinox occurs at the moment when the Earth’s axis doesn’t tilt toward or away from the sun. Someone standing on the equator on an equinox can observe the sun passing directly overhead. Additionally, equinoxes are the only two times a year that the sun rises due east and sets due west.
For centuries, people have celebrated the vernal equinox. At the ruins of Chichen Itza, the ancient Maya city in Mexico, crowds now gather on the spring (and fall) equinox to watch as the afternoon sun creates shadows that resemble a snake moving along the stairs of the 79-foot-tall Pyramid of Kukulkan, also called El Castillo.
On the spring equinox, the snake descends the pyramid until it merges with a large, serpent head sculpture at the base of the structure. While the Maya were skilled astronomers, it’s unknown whether they specifically designed the pyramid to align with the equinox and create this visual effect. Continue reading from History
Vernal Equinox (Encyclopedia Britannica)
First Day of Spring: The Spring Equinox (Farmer's Almanac)
Vernal Equinox Oddities: Lots to Learn About the First Day of Spring (Farmer's Almanac)
The March Equinox (Time and Date)
The Seasons, Equinox and the Solstices (National Weather Service)
What Is the Spring Equinox? (Smithsonian Blog)
The Spring Equinox is Here. What Does that Mean? (PBS WHYYY)
