First day of fall: why is the equinox not as egalitarian as it is believed to be?

See why in autumn the leaves have a unique color 0:42

(CNN) -

Twice a year, everyone on Earth is seemingly on an equal footing, at least when it comes to the distribution of light and dark.

This Wednesday, September 22, we enter our second and last equinox in 2021. If you reside in the northern hemisphere, you know it as the autumnal equinox (or autumnal equinox).

For people south of the equator, this equinox actually signals the arrival of spring.

People who are very close to the equator have 12-hour days and 12-hour nights all year round, so they don't notice anything.

However, people near the poles, in places like northern Canada, Norway and Russia, experience sudden changes in the day / night ratio every year.

They have long dark winters and summers where night hardly gets in the way.

But during the equinoxes, everyone, from pole to pole, enjoys a 12-hour split between day and night.

There's just one problem: it's not as perfectly "the same" as you've been told.

There is a good explanation (SCIENCE!) Why there are not exactly 12 hours of light on the equinox.

You will find more information about this later in the article.

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

Where does the word equinox come from?

From our CNN Fast Facts archive: The term equinox comes from the Latin word

equinoxium

, which means equality between day and night.

advertising

When exactly does the autumnal equinox occur?

The equinox will arrive at 19:21 UTC (Coordinated Universal Time) on September 22.

For people in places like Toronto and Washington, that's 3:21 p.m. local time.

In the west, in Los Angeles and Vancouver, that means it arrives at 12:21 pm For residents of Madrid, Berlin and Cairo, it arrives precisely at 9:21 pm If we go further east, Dubai marks the exact event at 11:21 pm

If we go even further into Asia, we end up changing the day.

For Bangkok residents, it is 2:21 a.m. on Thursday, September 23, while Singapore and Hong Kong times 3:21 a.m. You can click here to see more cities (rounded one minute down and adjusted for daylight saving time ).

• Bowie's "Starman" and Other Out-of-this-World Songs for a Spacewalk

Is the autumnal equinox the first official day of fall?

Yes. Fall officially begins on the autumnal equinox.

But there are actually two measurements of the seasons: "astronomical stations" (which follow the arrival of the equinoxes and solstices) and what are called "weather stations."

Allison Chinchar, a CNN meteorologist, explains the differences: "Astronomical fall is essentially the period of time from the autumnal equinox to the winter solstice. Those dates may vary a day or two each year, but this year they are. from September 22 to December 21, "he says.

"The meteorological autumn is different ... in the sense that the dates never change and are based on the weather stations and not on the angle of the Earth with respect to the sun. These are perhaps the seasons with which most people are familiar. "says Chinchar.

The sun rises behind the Washington Monument in the United States capital.

(Photo: J. David Ake / AP)

The meteorological stations are defined as the following: from March 1 to May 31 is spring;

from June 1 to August 31 is summer;

from September 1 to November 30 is autumn;

and from December 1 to February 28 is winter.

"This makes some dates difficult," says Chinchar.

"For example, December 10, most people would consider it winter, but if you use the astronomical calendar, it is technically still considered fall because it is before the winter solstice."

The expert affirms that "meteorologists and climatologists prefer to use the 'meteorological calendar' because not only do the dates do not change - which makes it easy to remember - but also because it is more in line with what people think traditional seasons are. ".

Why does the autumnal equinox occur?

The Earth rotates along an imaginary line that goes 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 is tilted 23.5 degrees, as explained by NASA.

That causes one hemisphere of the planet to receive more sunlight than the other during half the orbit of the year around the Sun. This discrepancy in sunlight is what triggers the seasons.

The effect is highest at the end of June and at the end of December.

Those are the solstices, and they are the most extreme differences between day and night, especially near the poles.

(This is why there is so much daily light during the summer in places like Scandinavia and Alaska.)

But since the summer solstice three months ago, in June, you will have noticed that our days have progressively shortened in the northern hemisphere and the nights have lengthened.

And now we are on the autumnal equinox.

Archaeological zones to welcome spring in Mexico 1:09

What did our ancestors know about all this?

Long before the age of clocks, satellites, and modern technology, our ancient ancestors knew a lot about the movement of the sun across the sky, enough to build huge monuments and temples that, among other things, served as giant calendars for mark stations.

These are some of the places associated with the equinox and the annual passage of the sun:

-

Stonehenge (United Kingdom): There are still many mysteries about these giant slabs, but we know that they were designed to mark the annual passage of the sun.

Although lined to highlight the summer and winter solstices, Stonehenge is also in the spotlight at this time of year.

- The Megalithic Temples of Malta: These seven temples on the Mediterranean island are some of the world's first independent stone constructions, dating back between 5,000 and 6,000 years ago.

In the Hagar Qim and Mnajdra temples, the semicircular chambers are aligned so that the rising sun on an equinox is framed between the stones.

- Chichén Itzá (Yucatán Peninsula, Mexico): El Castillo, the famous pyramid of Chichén Itzá, offers a striking spectacle on the equinoxes.

Built by the Mayan people between 1050 and 1300, the pyramid was built to cast a shadow during the equinoxes on the north balustrade of the Castle.

It looks like the shape of a snake gliding down the stairs, and the ancient special effect is enhanced by the sculpted beast heads on the base.

- Jantar Mantar (New Delhi, India): Of much more recent origin (1724 and 1730), these buildings from the late Mughal period are astronomical observatories.

What are some festivals, myths and rituals that still endure?

Around the world, the autumnal equinox has become woven 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.

The Chinese and Vietnamese continue to celebrate the Harvest Moon (also known as the Mid-Autumn Festival).

Lanterns line the streets as people say thank you, watch the moon, and eat.

Round cakes called mooncakes are a Mid-Autumn Festival favorite.

It is celebrated on the 15th day of the eighth lunar month of the Chinese calendar.

In 2021, it fell on September 21, the day before the equinox.

Britain's beloved harvest festivals have their roots in the autumnal equinox since pagan times.

In Japan, the Autumn Equinox Day is a national holiday.

In Japanese, it is known as Shubun no Hi (秋分 の 日), according to the Coto Japanese Academy.

The roots of the celebration are believed to go back to Shintoism and Buddhism.

Autumn leaves put on a show at Showa Kinen Park in Tokyo.

(Photo: courtesy of Takashi Hososhima, creative commons)

Are the Northern Lights really most active on the equinoxes?

Yes, at this time of year they usually offer a bigger show.

It turns out that the autumnal equinox and spring (or spring equinox) usually coincide with the peak of activity of the northern lights.

These beautiful and fascinating geomagnetic storms tend to be most active in March and April, and again in September and October, based on 75 years of historical records analyzed by solar physicist David Hathaway of the Marshall Space Flight Center in Huntsville, Alabama.

So why isn't the equinox exactly the same?

It turns out that there is actually a bit more light than darkness at the equinox, depending on where you are on the planet.

How does this happen?

The answer is a bit complicated, but fascinating.

As the US National Weather Service explains, the "almost" equal hours of day and night are due to the complex way of measuring sunrise and the refraction of sunlight in our atmosphere.

This bending of the light rays causes the Sun to 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 the Sun takes longer to rise and set the closer it gets to the poles.

So on the autumnal equinox, the length of the day will vary a bit depending on where you are.

Here are some breakdowns to give you a rough idea:

- At the equator: about 12 hours and 6 minutes (Quito, Nairobi, in Kenya, and Singapore are all close to the equator)

- At 30 degrees latitude: about 12 hours and 8 minutes (Houston, in Texas, Cairo and Shanghai, China)

- At 60 degrees latitude: about 12 hours and 16 minutes (Helsinki, in Finland, and Anchorage, Alaska)

To obtain true equality between day and night, you have to wait until days or even weeks after the official equinox.

That day is called

equilux

, and when it occurs depends on your latitude.

autumn equinox