5 Surprising Facts About the Spring Equinox

Goodbye, winter! Spring is almost here — at least for some of us. In the Northern Hemisphere, the first day of the season falls in late March during the phenomenon known as the spring equinox, or the vernal equinox (with 'vernal' meaning 'spring').

On this remarkable day, the sun aligns directly above the equator, a rare event that occurs just twice a year: once during the spring equinox and again during the autumnal equinox in September. (For those in the Southern Hemisphere, the March equinox is referred to as the fall or autumnal equinox.) The 2023 spring equinox will take place on March 20 at 5:24 p.m. EDT. To satisfy your astronomical curiosity, here are five interesting facts about it.

1. The Term "Equinox" Signifies "Equal Night"

Let’s dive into the origins of the word. Derived from Latin, equinox translates to "equal night." The Latin word for "even" is "aequi", while "nox" stands for "night."

During an equinox, the lengths of day and night are almost identical — but not perfectly. This phenomenon is tied to the Earth's movement. The planet’s axis is tilted at a 2-degree angle relative to its orbit around the sun.

An equinox represents the exact moment the sun crosses an invisible line in the sky. Imagine a huge, imaginary ring around Earth, sitting directly above the equator. Scientists refer to this theoretical halo as the celestial equator. It’s a line the sun crosses only twice annually — once during the spring equinox and once more during the autumn equinox. Because of the solar angle, every region of Earth will experience nearly 12 hours of daylight and 12 hours of darkness on March 20. (Technically, the day will be a few minutes longer than the night.)

2. Climate Experts Acknowledge a Different "First Day of Spring"

Traditionally, the March Equinox marks the arrival of spring in the Northern Hemisphere (and autumn in the Southern Hemisphere). However, did you know there's another possible starting date for the season?

Astronomers define the seasons based on Earth's orbit around the sun. According to the astronomical calendar, both spring and autumn begin with an equinox, while summer and winter commence with a solstice. These are the two key biannual dates when one hemisphere experiences its shortest day of the year.

If we follow the astronomical calendar, spring in the Northern Hemisphere in 2023 will span from March 20 to the summer solstice on June 20. However, climate scientists do not use this system. They adhere to the 'meteorological calendar,' where the year is split into four seasons of three months each. According to this calendar, spring starts on March 1 and continues through April and May. Meteorologists prefer this system because it relies on temperature cycles, which make it easier to calculate statistics and predict trends using consistent months and dates each year.

3. The Spring Equinox Marks the Persian New Year

"Navroz Mobarak!" The precise moment of the vernal equinox marks the beginning of the first month in the Iranian solar calendar. It also signifies the start of Nowruz, a grand, 13-day celebration often referred to as the Persian New Year. Observed by 300 million people worldwide, primarily in Central and Western Asia, Nowruz is preceded by a flurry of spring cleaning. Afterward, families indulge in lavish meals and may paint eggs, symbolizing fertility. On the last Tuesday before the equinox, people engage in a ritual of jumping over bonfires, representing the renewal the new year brings. Additionally, children visit homes, banging pots and requesting treats. The final day of the festivities is marked by a family picnic, as staying indoors is considered bad luck.

4. And Other Holidays Too, Like Easter

For centuries, followers of Shintoism have celebrated the solar event as a way to honor their ancestors. In 1948, the Japanese government made this tradition official by converting it into Vernal Equinox Day, a secular national holiday. It continues to be observed to this day.

In most branches of Christianity, Easter is celebrated on the Sunday following the first full moon after March 21. What's significant about this date? It marks the ecclesiastical Spring Equinox. While astronomers know that the spring equinox can occur on March 19, 20, or 21, many church leaders simplify matters by designating March 21 as the official equinox date each year. As a result, Easter can fall as early as March 22 or as late as April 25.

On this day, a snake-like shadow appears to crawl down one side of the El Castillo pyramid in Mexico, possibly in homage to a serpent deity (refer to the 'Now That's Cool' section at the end of the article for further details).

5. Earth's Wobbling Will Affect Future Equinoxes

Much like a spinning top, Earth experiences a slight wobble on its axis. At present, the axis is pointed toward the famous 'north star,' Polaris. However, in 12,000 years, it will shift away from Polaris and point toward a new star: Vega. This cycle will continue repeating every 26,000 years.

The Earth's wobble is caused by gravitational forces from the sun and moon, and as the planet wobbles, the sun's relationship with the zodiac changes. Currently, during the vernal equinox, the sun aligns with the constellation Pisces. However, before 68 B.C.E., it lined up with Aries. By the year 2567, the sun will align with the constellation Aquarius.