The first day of autumn has arrived.  Here’s how the equinox marks the seasons.

The first day of autumn has arrived. Here’s how the equinox marks the seasons.

FILE PHOTO: This color image of Earth, taken by NASA's Earth Polychromatic Imaging Camera, a four-megapixel CCD camera and telescope, on July 6, 2015, and released on July 20, 2015. REUTERS/NASA/Handout via Reuters/File Photo

A view of Earth taken by NASA’s Earth Polychromatic Imaging Camera.Reuters

  • Autumnal or autumnal equinox 2022 takes place on Thursday 22 September.

  • The autumnal equinox occurs when the sun’s warm rays line up perfectly with the earth.

  • During an equinox at Earth’s equator, the sun appears almost directly overhead.

Thursday is this year’s Autumnal Equinox.

This astronomical event, which occurs every year, means that the day is about the same length as the night.

Also called the September or autumnal equinox, this event marks the official start of autumn and the end of summer as the Northern Hemisphere moves towards colder and darker days.

For those in the southern hemisphere, the milestone marks the beginning of spring.

There are two reasons for these important seasonal shifts: the tilt of the Earth’s axis and the planet’s orbit around the Sun.

How the autumnal equinox works

In June and December, the earth hits its solstices – the longest and shortest days of the year.

And twice a year, in March and September, the Earth reaches the equinox, which means that the days and nights are roughly the same length.

Earth equinox and solstice graphics

How the Earth, its axial tilt and the Sun work to create the solstices, equinoxes and seasons.Shayanne Gal/Business Insider

This is why: the sun rises and sets on our planet once a day because our planet also rotates on its axis.

But it takes about a year — about 365 days, 5 hours, 59 minutes and 16 seconds to be more precise — for the Earth to orbit the Sun, according to NASA.

The Earth’s axis is not perfectly square to the plane of its orbit around the Sun. Instead, the axis is slightly tilted to one side, about 23.5 degrees (for now).

This means that the sun’s rays hit different parts of the world at different angles, depending on the time of year.

When the Earth tilts towards the Sun, in summer, more sunlight can hit the Earth and it can heat the atmosphere. But when the Earth is tilted away, in winter, less sunlight hits the Earth, and the atmosphere is cooler.

During an equinox, however, the earth is perfectly aligned with the sun’s warm rays. This means that the most intense rays of the sun hit the earth directly at the equator, and day and night last about the same length.

Earth during the equinox

An illustration of the Earth during an equinox.Shayanne Gal/Business Insider

This year, this will happen at exactly 9:03 PM ET.

If you were to stand directly on the equator at the moment the equinox peaks, the day would last about 12 hours and six and a half minutes. The sun would appear more or less directly overhead and your shadow would also be as small as it would ever be.

But this moment does not last, as the Earth orbits the Sun at a speed of approximately 66,600 mph.

An animation below provides an overview of how this works:

equinoxall

An animation of the Earth as it orbits, with points marking both equinoxes and solstices along with relevant information.James O’Donoghue

Uneven seasons

Our planet’s orbit around the sun is not a perfect circle. It is actually slightly elliptical, and the center of gravity is slightly offset from the sun, so the time it takes to cycle through the seasons is not completely divided.

About 89 days and 19 hours after the autumnal equinox, Earth will reach its winter solstice – when the most direct sunlight hits the southern tropic (or Tropic of Capricorn). Another 89 days later, the vernal or vernal equinox will occur.

Then there are another 93 days and 18 hours until the summer solstice—when the most direct rays of the sun reach their northernmost latitude, called the Northern Tropic (or Tropic of Cancer)—and another 92 days and 16 hours until the return to the autumnal equinox.

People, some in traditional dress, hold their hands up to the sky, with Stonehenege in the background.

Druids, pagans and others gather around Stonehenge on September 23, 2017.Matt Cardy/Getty Images

Celebrates the equinox

For some, the equinox is more than a day that brings the return of the pumpkin spice latte. It has marked the arrival of the fall season for many throughout human history, and several cultures still mark the event today per USA Today.

An example is at Stonehenge in Great Britain, where pagans and druids gather around the monolithic structure to watch the sun rise over the stones.

Dave Mosher contributed to an earlier version of this article

Read the original article on Business Insider

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