Autumn equinox 2020: When does autumn officially start in the UK?

Autumn marks the transition from summer to winter in the Northern Hemisphere
Autumn in the UK
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The UK may have just had more than a week of sunshine, but Monday is the last day of summer.

Autumn is just around the corner, with the first day of the new season coming on Tuesday.

For astronomers Tuesday, September 22nd marks the first day of autumn in the Northern Hemisphere for 2020 – a season also known as fall in the US.

So as head into the new season, here's all you need to know about the the 2020 autumn equinox.

Soon you'll be able to hear the crunch of leaves under foot
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What is the Autumn equinox?

An equinox is a phenomenon which only happens twice a year - once during spring and once again in the autumn.

It happens when the sun positions itself exactly above the equator between the Northern and Southern Hemisphere.

For those in the Northern Hemisphere, the autumn equinox marks the beginning of autumn and for those in the southern it marks the beginning of spring.

Once the equinox hits in the autumn the nights become longer than the day, while the opposite happens after the spring equinox.

The term "equinox" stems from the Latin word "equi," meaning equal and "nox," meaning night.

When is the Autumn Equinox?

This year, the Autumn equinox takes place on September 22 at 2.30pm BST.

The autumn equinox always falls on one of three days towards the end of September.

The date varies because of the difference between how the Gregorian calendar calculates a year (365 days) and the time it takes for the Earth to complete its orbit around the sun, which is 365.25 days.

Because of the difference in the days, it means each September the equinox occurs around six hours earlier than the previous year.

When does meteorological autumn begin?

But according to the meteorological calendar autumn starts on September 1 and ends on November 30.

The seasons have different start and end dates because they are measured differently by different groups.

The astronomical seasons are based on the position of earth in relation to the sun while the meteorological seasons on the other hand are calculated using annual temperature cycles.

In the meteorological calendar autumn is from September to the end of November, winter runs from December to the end of February, spring is March, April and May while summer is June, July and August.

How is the Autumn equinox celebrated?

People travel to the Chichen Itza pyramid in Mexico to mark the Autumn Equinox
Filip Gielda/Unsplash

People have been commemorating the Autumn equinox for centuries.

Ancient peoples such as the Druids in England and the Maya in Central America see it as a marker of the harvest season.

During the Autumn equinox, neo-druids gather at Stonehenge to perform rituals.

In Mexico, crowds flock to the pyramid at Chichen Itza on the Yucatan Peninsula. A serpent-headed statue is placed at the foot of the pyramid and as the sun sets, the sunlight and the shadow show the body of the serpent joining with the head.