First day of autumn: Why the equinox is not as equal as you might think

(CNN) – Twice a year the sun does not play favorites. Everyone on Earth is seemingly on equal footing – at least when it comes to the amount of light and darkness they receive.

We have entered our second and final equinox of 2022. If you live in the Northern Hemisphere, you know it as the autumnal equinox (or autumnal equinox). For people south of the equator, this equinox is actually the arrival of spring.

Your location in the world also determines whether you mark the day this year on Thursday, September 22 or Friday, September 23. People in America will celebrate on Thursday; time zone differences mean people in Africa, Europe and Asia will mark it on their Friday.

People who are really close to the equator have about 12 hour days and 12 hour nights all year round, so they won’t really notice a thing. But hardy people near the poles, in places like Alaska and the northern parts of Canada and Scandinavia, go through wild swings in the day/night ratio every year. They have long, dark winters and then they have summers where the night barely penetrates.

But during equinoxes, everyone from pole to pole gets to enjoy a 12-hour split of day and night. Well, there’s just one rub—it’s not as perfectly “equal” as you might have thought.

There is a good explanation (SCIENCE!) for why you don’t get it exactly 12 hours of daylight on the equinox. More on that further down.

But first, here are the answers to your other burning equinox questions:

Where does the word ‘equinox’ come from?

From our CNN Fast Facts file: The term equinox comes from the Latin word equinoxium, which means “equality between day and night.”

Exactly when does the autumnal equinox occur?

The setting sun is seen looking west on Randolph Street in Chicago just days before the fall equinox in 2019.

Terrence Antonio James/Chicago Tribune/Getty Images

For people in places like Toronto and Washington, DC, that’s 9:03 a.m. local time. It arrives at 8:03 PM in Mexico City and Chicago. Out West in San Diego and Vancouver, which means it arrives at 6:03 p.m

But go in the other direction across the Atlantic, and the time change puts you in Friday. For residents of Madrid, Berlin and Cairo, it arrives at 3:03 a.m. on Friday. Immediately to the east, Dubai marks the exact event at 5:03 p.m

For residents of Bangkok, it is 8:03 a.m. while Tokyo clocks in at 10:03 a.m. You can click here to see more cities (rounded by one minute and adjusted for daylight saving time).

Is the autumnal equinox the official first day of fall?

Yes. Autumn officially begins on the autumnal equinox.

But there are actually two measures of the seasons: “the astronomical seasons” (which follow the arrivals of equinoxes and solstices) and what is called the “meteorological seasons”.

Allison Chinchar, CNN meteorologist, explains the differences:

“Astronomical autumn is essentially the time period from the fall equinox to the winter solstice. Those dates can vary by a day or two each year,” she says.

“Meteorological autumn is different… in that the dates never change and are based on climatic seasons rather than the angle of the Earth relative to the sun. These are perhaps the seasons that more people are familiar with,” says Chinchar.

Fall foliage can come early in high-elevation places like Kenosha Pass, Colorado.  This photo was taken on September 19, 2016, at night with a long exposure, illuminated by moonlight and passing car headlights.

Fall foliage can come early in high-elevation places like Kenosha Pass, Colorado. This photo was taken on September 19, 2016, at night with a long exposure, illuminated by moonlight and passing car headlights.

RJ Sangosti/Denver Post/Getty Images

Meteorological seasons are defined as the following: March 1 to May 31 is spring; June 1 to August 31 is summer; September 1 to November 30 is autumn; and December 1 to February 28 is winter.

“This makes some dates difficult,” says Chinchar. “For example, December 10th is what most people would consider winter, but if you use the astronomical calendar, that’s still technically considered fall because it’s before the winter solstice.”

She said that “meteorologists and climatologists prefer to use the ‘meteorological calendar’ because not only do the dates not change – making it easy to remember – but also because it falls more in line with what people think of as traditional seasons .”

Why does autumnal equinox occur in the first place?

The rising sun tries to break through the fog near the town of Glastonbury in southwest England on autumnal equinox 2021.

The rising sun tries to break through the fog near the town of Glastonbury in southwest England on autumnal equinox 2021.

Matt Cardy/Getty Images

The Earth rotates along an imaginary line that runs from the North Pole to the South Pole. It is called the axis, and this rotation is what gives us day and night.

However, the axis tilts at 23.5 degrees, as NASA explains. That allows one hemisphere of the planet to receive more sunlight than the other for half of the year’s orbit around the sun. This discrepancy in sunlight is what triggers the seasons.

The effect is at its maximum at the end of June and the end of December. These are the solstices, and they have the most extreme differences between day and night, especially at the poles. (That’s why it stays light so long every day in the summer in places like Scandinavia and Alaska.)

But since the summer solstice three months ago in June, you have noticed that our days in the northern hemisphere are gradually getting shorter and the nights longer. And now here we are at the autumnal equinox!

What did our ancestors know about all this?

Long before the time of clocks, satellites and modern technology, our ancient ancestors knew a lot about the movement of the sun across the sky – enough to build massive monuments and temples that, among other purposes, served as giant calendars to track the to mark seasons.

Here are just a few of the places associated with the equinox and the annual passage of the sun:

• Megalithic Temples of Malta: These seven temples on the Mediterranean island are some of the earliest free-standing stone buildings in the world, dating back 5,000 to 6,000 years ago. At the Hagar Qim and Mnajdra temples, the semicircular rooms are laid out so that the rising sun is surrounded by the stones on an equinox.
Chichen Itza

Mexico’s Chichen Itza is sacred ground during the spring and autumn equinoxes.

Getty Images / zxvisua

• Chichén Itzá (Yucatán Peninsula, Mexico): El Castillo, the famous pyramid at Chichén Itzá, puts on a striking show on the equinoxes. Built by the Toltec-Maya people between 1050 and 1300, the pyramid was built to cast a shadow at equinoxes on the northern balustrade of El Castillo. It resembles the form of a serpent gliding down the stairs, and the ancient special effect is increased by the heads of sculptured animals at the base.
• Jantar Mantar (New Delhi, India): Very recent in origin (1724 and 1730), these buildings from the end of the Mughal period are astronomical observatories.

What are some festivals, myths and rituals still with us?

All over the world, the autumnal equinox has woven its way into our cultures and traditions.

In Greek mythology, the autumnal equinox marks the return of the goddess Persephone to the underworld for three months, where she is reunited with her husband, Hades.
Chinese and Vietnamese people still celebrate the Harvest Moon (also known as the Mid-Autumn Festival). Lanterns line the streets as people give thanks, watch the moon and eat. Round pastries called mooncakes are a favorite of Mid-Autumn Festival. It is held on the 15th day of the eighth lunar month on the Chinese calendar. In 2022 it fell on September 10.

Britain’s favorite harvest festivals have their roots in the autumnal equinox since pagan times.

Rikugien, Tokyo fall leaves

Rikugien Gardens in Tokyo are ablaze in autumn color. Fall equinox is a national holiday in Japan.

courtesy Kimon Berlin

Are the Northern Lights really active during the equinoxes?

Yes – they often put on more of a show this time of year.

It turns out that the autumn equinox and spring (or vernal equinox) usually coincide with peak activity with the aurora borealis.

So why isn’t the equinox exactly equal?

It turns out that you actually get a little more daylight than darkness on the equinox, depending on where you are on the planet. How does that happen? The answer is a bit complicated, but fascinating.

As the US National Weather Service explains, the “almost” equal hours are day and night because of the complex way a sunrise is measured and the refraction of sunlight in our atmosphere.
The evening sun shines through the autumn colored leaves on chestnut trees on the banks of the Landwehrkanal in the Kreuzberg district of Berlin.

The evening sun shines through the autumn colored leaves on chestnut trees on the banks of the Landwehrkanal in the Kreuzberg district of Berlin.

Stefan Jaitner/dpa/picture-alliance/AP

This bending of light rays makes the sun appear above the horizon when the actual position of the sun is below the horizon. The day is slightly longer at higher latitudes than at the equator because it takes the sun longer to rise and set the closer you get to the poles.

So on autumnal equinox the length of the day will vary slightly depending on where you are. Here are a few breakdowns to give you a rough idea:

• At or near the equator: about 12 hours and 6 minutes (Quito, Ecuador; Nairobi, Kenya; and Singapore)

• At or near 30 degrees north latitude: approximately 12 hours and 8 minutes (New Orleans, Louisiana; Cairo, Egypt; and Shanghai, China)

• At or near 60 degrees north: approximately 12 hours and 16 minutes (Helsinki, Finland and Anchorage, Alaska)

For the truly equal day/night split, you have to wait until days or even weeks after the official equinox. That day is called the equilux, and when it happens depends on your latitude.