Autumn Equinox: What is it and why does it happen?

·2-min read
 (Google Doodle)
(Google Doodle)

When lockdown was established in the UK in March, the weather was still somewhat chilly, the season of spring having only just officially begun.

Since then, the nation has experienced the full might of summer, with sweltering heatwaves being recorded across the nation.

Almost six months to the day that lockdown was implemented, the autumn equinox has arrived, an occasion that has been marked today with an autumnal Google Doodle.

What is the autumn equinox and why does it happen?

The autumn equinox always takes place in September, either falling on the 22nd or 23rd day of the month.

An equinox occurs twice in the year when the Sun "sits right above Earth’s Equator", National Geographic states.

The Royal Observatory in Greenwich, London explains that the Earth, which tilts on its axis, orbits the Sun.

“As it orbits the Sun, the Sun illuminates the northern or southern hemisphere more depending on where the Earth is along its orbit,” the museum states.

“However, at two points in the year the Sun will illuminate the northern and southern hemispheres equally. These are known as the equinoxes.”

This also means that in the northern hemisphere when autumn officially begins, at the same time spring is commencing in the southern hemisphere.

UK news in pictures

21 September 2022: A flock of birds in the sky as the sun rises over Dungeness in Kent (PA)
21 September 2022: A flock of birds in the sky as the sun rises over Dungeness in Kent (PA)
20 September 2022: Flowers which were laid by members of the public in tribute to Queen Elizabeth II at Hillsborough Castle in Northern Ireland are collected by the Hillsborough Gardening Team and volunteers to be replanted for those that can be saved or composted (PA)
20 September 2022: Flowers which were laid by members of the public in tribute to Queen Elizabeth II at Hillsborough Castle in Northern Ireland are collected by the Hillsborough Gardening Team and volunteers to be replanted for those that can be saved or composted (PA)
19 September 2022: The ceremonial procession of the coffin of Queen Elizabeth II travels down the long walk as it arrives at Windsor Castle for the committal service at St George’s Chapel (AFP/Getty)
19 September 2022: The ceremonial procession of the coffin of Queen Elizabeth II travels down the long walk as it arrives at Windsor Castle for the committal service at St George’s Chapel (AFP/Getty)
18 September 2022: A man stands among campers on The Mall ahead of the Queen’s funeral (Reuters)
18 September 2022: A man stands among campers on The Mall ahead of the Queen’s funeral (Reuters)
17 September 2022: Wolverhampton Wanderers’ Nathan Collins fouls Manchester City’s Jack Grealish leading to a red card. City went on to win the match at Molineux Stadium three goals to nil. (Action Images/Reuters)
17 September 2022: Wolverhampton Wanderers’ Nathan Collins fouls Manchester City’s Jack Grealish leading to a red card. City went on to win the match at Molineux Stadium three goals to nil. (Action Images/Reuters)
16 September 2022: Members of the public stand in the queue near Tower Bridge, and opposite the Tower of London, as they wait in line to pay their respects to the late Queen Elizabeth II, in London (AFP via Getty Images)
16 September 2022: Members of the public stand in the queue near Tower Bridge, and opposite the Tower of London, as they wait in line to pay their respects to the late Queen Elizabeth II, in London (AFP via Getty Images)
15 September 2022: Members of the public in the queue on in Potters Fields Park, central London, as they wait to view Queen Elizabeth II lying in state ahead of her funeral on Monday (PA)
15 September 2022: Members of the public in the queue on in Potters Fields Park, central London, as they wait to view Queen Elizabeth II lying in state ahead of her funeral on Monday (PA)
14 September 2022: The first members of the public pay their respects as the vigil begins around the coffin of Queen Elizabeth II in Westminster Hall, London, where it will lie in state ahead of her funeral on Monday (PA)
14 September 2022: The first members of the public pay their respects as the vigil begins around the coffin of Queen Elizabeth II in Westminster Hall, London, where it will lie in state ahead of her funeral on Monday (PA)
13 September 2022: Crowds cheer as King Charles III and Camilla, Queen Consort arrive for a visit to Hillsborough Castle (Getty)
13 September 2022: Crowds cheer as King Charles III and Camilla, Queen Consort arrive for a visit to Hillsborough Castle (Getty)
12 September 2022: Crowds line the Royal Mile, Edinburgh, as King Charles III joins a procession from the Palace of Holyroodhouse to St Giles’ Cathedral following the coffin of Queen Elizabeth II (Katielee Arrowsmith/SWNS)
12 September 2022: Crowds line the Royal Mile, Edinburgh, as King Charles III joins a procession from the Palace of Holyroodhouse to St Giles’ Cathedral following the coffin of Queen Elizabeth II (Katielee Arrowsmith/SWNS)
11 September 2022: Members of the Public pay their respects as the hearse carrying the coffin of Queen Elizabeth II, draped in the Royal Standard of Scotland, is driven through Ballater (AFP/Getty)
11 September 2022: Members of the Public pay their respects as the hearse carrying the coffin of Queen Elizabeth II, draped in the Royal Standard of Scotland, is driven through Ballater (AFP/Getty)

Encyclopædia Britannica adds that the autumn equinox in the northern hemisphere marks just one of two times of the year when “the Sun is exactly above the Equator and day and night are of equal length”.

The autumn season lasts until winter, which begins this year on 21 December according to the astronomical season, the Met Office states.

When is the spring equinox?

The spring equinox in the northern hemisphere is the second of the two times of the year when day and night are of equal length.

The 2021 spring equinox, marking the official start of spring, will take place on Saturday 20 March.