What Is Meant By Spring Equinox?

The vernal equinox, or the first day of spring, starts every year on March 19 or 20, depending on where you live in the Northern Hemisphere. But what is an equinox, and who decided that it should be the first day of spring? The answers to these questions are not as simple as you might think.

 

Before you can understand what an equinox is, you need to know a bit about how our solar system works. The tilt of the earth's axis is 23.5 degrees, and the earth spins on it. One rotation takes 24 hours to finish. As the earth spins on its axis, it also moves in a 365-day circle around the sun.

 

As the planet goes around the sun once a year, it slowly tilts on its axis. The Northern Hemisphere, which is the part of the Earth above the Equator, gets more sunlight than the Southern Hemisphere for half the year. The Southern Hemisphere gets more sunlight than the Northern Hemisphere. But on two days of the year, there is the same amount of sunlight in both hemispheres. The Latin word for these two days is equinox, which means "equal nights."

 

The vernal (Latin for "spring") equinox happens in the Northern Hemisphere on March 19 or 20, depending on your time zone. The autumnal equinox, which marks the start of fall, happens on either September 21 or September 22, (depending on time zone). These equinoxes are backwards in the Southern Hemisphere.

 

On these days, both day and night last 12 hours, but because of how the atmosphere bends light, day can last up to 8 minutes longer than night. Depending on things like air pressure and humidity, this effect causes the sun's rays to bend around the earth's shape. This lets the light to stay out after sunset and come out before sunrise.

 

There is no rule that says spring has to start on the vernal equinox. People have been keeping track of the seasons and celebrating them based on how long or short the days are since the beginning of time. The Gregorian calendar, which linked the changing of the seasons to the equinoxes and solstices, made this tradition official in the West.

 

If you live in North America in 2018, the spring equinox starts at 6:15 a.m. in Honolulu, Hawaii; 10:15 a.m. in Mexico City; and 1:45 p.m. in St. John's, Newfoundland, Canada. But since the earth doesn't go around the sun in exactly 365 days, the date of the spring equinox changes every year. In 2018, the equinox starts at 12:15 p.m., Eastern Daylight Time, in New York City. In 2019, it doesn't start until March 20 at 5:58 p.m. But in 2020, the equinox will start at 11:49 p.m. the night before.

 

On the March Equinox, at the North Pole, the sun is on the horizon of the earth's surface. On the March Equinox, the sun rises at noon and goes all the way to the horizon. The North Pole stays lit until the Autumn Equinox. At the South Pole, the sun goes down at noon after being up for six months straight (since the autumnal equinox).

 

The two annual solstices are not like the two equinoxes, when days and nights are the same length. Instead, they are the days when the northern and southern hemispheres get the most and least sunlight. They also mark the start of winter and summer. The summer solstice happens on June 20 or 21, depending on the year and where you live in the Northern Hemisphere. This is the day with the most hours of daylight north of the equator. In the Northern Hemisphere, the winter solstice takes place on December 21 or 22. This is the shortest day of the year. In the Southern Hemisphere, it's the other way around. Winter begins in June, summer in December.

 

If you live in New York City, the summer solstice will happen on June 21 at 6:07 a.m. and the winter solstice will happen on December 21 at 5:22 p.m. On June 20, 2019, the summer solstice begins at 11:54 a.m., but on June 20, 2020, it happens at 5:43 p.m. In 2018, the winter solstice will happen at 5:22 p.m. on December 21. In 2019, it will happen at 11:19 p.m. on December 21. In 2020, it will happen at 5:02 a.m. on December 21.

 

People often think that you can only balance an egg on its end on the equinoxes, but this is just an urban legend that started in the U.S. after a 1945 article in Life magazine about a Chinese egg-balancing trick. You can anytime balance an egg on its bottom if you are patient and careful.