What is Autumn Equinox and how is the beginning of the autumn season celebrated?

Today is the autumn equinox - a day with exactly 12 hours of dark and 12 hours of light, officially the first autumn day in the northern hemisphere.

What is the autumn equinox?

An equinox occurs when the sun passes directly over the earth's equator, resulting in a day and night that are the same length.

There are two equinoxes every year - one around 22 March and one around 22 September.

In the southern hemisphere, the seasons are reversed and the September equinox marks the beginning of spring.

When is the autumn equinox?

This year the autumn equinox takes place on Monday 23 September.

The exact moment of equinox, when the sun is directly above the Earth's equator, is 8:50 am that day.

After this point, the days become shorter and the nights become longer until the winter solstice on December 22, when the pattern will reverse.

Why does the equinox happen?

The equinox takes place because of the tilt of the earth in relation to the sun. This is what causes the seasons.

During the summertime, the northern hemisphere is tilted towards the sun. So we get longer days as more light falls on this part of the surface.

In the winter it is the southern hemisphere that receives most of the light.

Equinoxes occur when the axis of rotation of the earth is exactly parallel to the direction of movement of the earth around the sun.

This means that the length of day and night is exactly 12 hours at all points on the earth's surface.

Equal night

The word equinox is Latin for "equal night".

Meteorologists use it as the official turning point in the seasons because, although it can vary from year to year, it ensures the most accurate registration.

It is celebrated all over the world - especially at the Chichen Itza Aztec monument in Mexico.

During the equinox, a strip of light makes its way through the monument at sunset and attracts crowds of spectators.

How is the start of the fall season celebrated?

The autumn equinox took place on Monday, September 23, with the precise moment of equinox, when the sun was directly above the earth's equator, at 8.50 am BST.

Hundreds of brave Britons left to participate in a huge skinny session on Sunday, September 22 in the chilly North Sea.

The event, which takes place every year in Druridge Bay, Northumberland, marks one of the two days of the year in which the path of the sun exactly follows the equator, and raises money for MIND mental health.

Jax Higginson, who is organizing the annual event, now in his eighth year, said: "It was huge and brilliant. There was a lot of fun and passion on the beach this morning.

"It's not just about taking off our clothes, it's also about taking risks, connecting with nature, celebrating life and embracing our own body.

"It always happens around the Fall Equinox and that is intentional. It is my way of thanking the summer and finding a way to make the transition to winter.

"People were splashing around and there were shouting and laughter, it was beautiful. It makes it all worthwhile.

"I think it was the warmest it has ever been."

The fundraising coincided with the last glorious summer weather, allowing many Britons to enjoy a last BBQ in the sun before the colder fall temperatures seep in.

For some, the equinox is a spiritual time, with druids and pagans who are particularly interested in the astronomical event.

In pagan beliefs, the equinox is also known as Mabon, Second Harvest or Alban Elfed, marking a time of thanksgiving for the harvest.

New-age spiritual people spend the morning in Stonehenge, where they will see the sunrise in a new season.

In some rural communities, it is traditional to drink dandelion and burdock syrups on the day of the equinox to cleanse the body and prepare for fall.

Others will celebrate by trying to balance an egg, thanks to the false urban legend that the equinox is the only day when egg balance is possible.

When is the autumn equinox in 2019?

This year the fall equinox in the northern hemisphere took place on September 23 - the same day as the start of the astronomical fall.

The autumn equinox marks the day when the northern hemisphere tilts slightly from the sun, which means that days become shorter and the temperature starts to cool down.

It is the day on which daylight hours and night times are equally long.

This continues until the winter solstice when the northern hemisphere begins to tilt back towards the sun on its axis.

Meteorological calendar of the seasons

Spring: March, April, May

Summer: June, July, August

Fall: September, October, November

Winter: December, January, February

When does autumn officially begin?

For astronomers, the equinox marks the end of summer and the beginning of autumn, which means that autumn has officially fallen.

So in 2019, the fall begins on September 23.

The end of autumn officially falls on December 21.

Meanwhile, meteorologists prefer to divide the year a little differently, with the fall taking place from September 1 to the end of November.

Whatever you use, we are now officially in the fall, so dig out your coats and put that BBQ away for another year.