The first day of autumn has arrived. This is how the equinox marks the change of seasons.

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

  • Fall 2022 or the fall equinox occurs on Thursday, September 22.

  • The fall equinox occurs when the sun’s warm rays square perfectly with the earth.

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

Thursday is the fall equinox this year.

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

Also called the September or Fall Equinox, this event means that fall officially begins and summer ends as the Northern Hemisphere heads toward cooler, darker days.

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

There are two reasons for these major seasonal changes: Earth’s tilted axis and the planet’s orbit around the sun.

How does the autumnal equinox work?

In June and December, Earth reaches its solstices, the longest and shortest days of the year.

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

Chart of equinoxes and terrestrial solstices

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

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

But it takes about a year – about 365 days, 5 hours, 59 minutes and 16 seconds to be precise – for the Earth to go around the sun, according to NASA.

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

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

When Earth is tilted toward the sun, during the summer, more sunlight can reach Earth and can warm the atmosphere. But when the Earth is tilted, during winter, less sunlight hits the Earth and the atmosphere is cooler.

However, during an equinox, the Earth squares perfectly with the warm rays of the sun. That means the sun’s strongest rays hit Earth directly at the equator, and day and night last about the same amount of time.

The earth during the equinox

An illustration of the earth during an equinox.Shayanne Girl/Business Insider

This year, this will happen at precisely 9:03 pm ET.

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

But this moment does not last, as the Earth revolves around the sun at a speed of approximately 66,600 mph.

An animation below provides an overview of how this works:

equinox

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

uneven seasons

Our planet’s orbit around the sun is not a perfect circle. In reality, it is slightly elliptical and its center of gravity is slightly offset from the sun, so the time it takes to go through the seasons is not perfectly distributed.

About 89 days and 19 hours after the fall 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 spring or vernal equinox will occur.

Then it’s another 93 days and 18 hours until the summer solstice, when the sun’s most direct rays reach its northernmost latitude, called the Tropic of North (or Tropic of Cancer), and another 92 days and 16 hours to go back to autumn. . equinox.

People, some in traditional garb, raise their hands to the sky, with Stonehenge in the background.

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

celebrating the equinox

For some, the equinox is more than just a day that comes with the return of pumpkin spice lattes. It has marked the arrival of harvest season for many throughout human history and various cultures still mark the event today according to USA Today.

One example is Stonehenge in the UK, 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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