Cherry Blossom trees are blooming early

Spring has finally sprung: The vernal equinox, the official start date for the season in the Northern Hemisphere, has arrived. The 2024 spring equinox occurred at exactly 11:06 p.m. EDT on Tuesday, March 19.

But why does the day mark the start of spring and why only in the Northern Hemisphere? 

What is an equinox?

There are only two equinoxes a year: vernal and autumnal. They happen when the sun is directly overhead at noon, creating nearly equal portions of day and night in a 24-hour period. The word equinox itself is derived from the Latin words aequus and nox, or equal night.

It usually falls on March 19, 20, or 21. A spring equinox on March 21 is rare, according to the Farmer's Almanac. There hasn't been one in the mainland U.S. for the entirety of the 21st century and there won't be one until 2101.

The date varies, in part, because Earth travels around the sun in 365.24 days, while a calendar year is 365 days, according to the National Centers for Environmental Information.

What's the difference between the spring equinox and meteorological spring?

While the 2024 vernal equinox falls on March 19, meteorological spring began at the start of the month. According to NASA, there are two types of seasons: meteorological and astronomical. 

Meteorological seasons are tied to the calendar and are based on the annual temperature cycle. Meteorological seasons are broken up into groupings of three months. Each year, meteorological spring lasts from March 1 until May 31. 

Astronomical seasons are based on the tilt of Earth's axis and Earth's position during its orbit around the sun.

When does spring start in the Southern Hemisphere?

In the Southern Hemisphere, spring starts in September, when fall begins in the Northern Hemisphere. 

The March equinox will bring later sunrises, earlier sunsets, chillier winds and dry, falling leaves in the Southern Hemisphere. The reverse is true in the Northern Hempisphere, where Tuesday's equinox will bring earlier sunrises, later sunsets, softer winds, and budding plants. 

Rituals, traditions and myths 

While Easter isn't until the end of March, there's an egg tradition tied to the equinox. According to a weather.gov post, Chinese tradition includes the belief that an egg can be made to stand on end at the exact moment when winter ends and spring stars. However, it's technically possible to stand an egg on end on any day of the year, as long as you have a large amount of patience. 

Nowruz, the Iranian or Persian New Year, is tied to the spring equinox. It's been celebrated for more than 3,000 years in the Balkans, the Black Sea Basin, the Caucasus, Central Asia, the Middle East and other regions, according to the United Nations.

When is the next solstice and equinox?

Those impatient for the start of summer need to wait for the summer solstice on Thursday, June 20. The autumnal equinox, signaling the start of fall, will be on Sunday, Sept. 22. The winter solstice this year falls on Saturday, Dec. 21.

In:
• Equinox

Aliza Chasan

Aliza Chasan is a digital producer at 60 Minutes and CBSNews.com. She has previously written for outlets including PIX11 News, The New York Daily News, Inside Edition and DNAinfo. Aliza covers trending news, often focusing on crime and politics.

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