The Autumn Equinox is the moment when the Sun appears to cross the celestial equator as it makes it journey southwards. This event is a key marker for the distinction between the seasons. It is the day when the northern hemisphere slightly tilts away from the sun marking the day when there is approximately equal amounts of daylight and darkness. But what actually is the Autumn Equinox and when is it this year?
Temperatures are beginning to drop and days are drawing to a close earlier in the day, but the official marker of the arrival of Autumn has not yet arrived.
The September Equinox, also known as the Autumn Equinox, is the moment when the Sun as viewed from the Equator rises due east and sets due west.
Before the Autumn Equinox, the Sun rises and sets more northerly and afterwards, it rises and sets more southerly.
It marks the end of summer and the beginning of autumn for the northern hemisphere, while conversely it marks the end of the winter and the start of the spring in the southern hemisphere.
Each year, there are four seasons: Spring, Summer, Autumn and Winter.
Throughout the year, there are one or two days when the length of the night and day are roughly the same, this is known as the Autumn and Spring equinox.
This means in most places around the world there will be approximately 12 hours of daylight and darkness.
They take place in September and March but the dates change according to the progression of the Sun.
Each year, the Autumn Equinox usually takes place between September 21 and 24.
So when is the Autumn Equinox this year?
This year, the Autumn Equinox will take place on Monday, September 23.
In the UK, the equinox will peak at exactly 8.50am BST (7.50am UTC).
Next year, the equinox will arrive on Tuesday, September 22, followed by Wednesday, September 22, in 2021.
You can find out more about how close to equal hours of sunlight and darkness you will see on the day of the Autumn Equinox here.
How is the Autumn Equinox commemorated?
The September equinox marked the first day of the French Republican Calendar.
The Autumn Equinox marks the first day of Mehr or Libra in the Iranian calendar and is one of the Iranian festivals called Jashne Mihragan, or the festival of sharing or love in Zoroastrianism.
In East Asia the Autumn Equinox is on the 15th day of the 8th lunar month, often near the autumnal equinox day, and is an official holiday in mainland China, Hong Kong, Taiwan and in many countries with a significant Chinese minority.
In Korea, Chuseok is a major harvest festival and a three-day holiday celebrated around the Autumn Equinox.
In the UK, the Autumn Equinox is commemorated as a traditional harvest festival.
Pagans observe the September equinox as a highly significant point in their calendar observing the day with the ritual of Mabon.
The ritual gives thanks for a plentiful harvest and recognises the need to share the Earth’s fruits in the coming winter months and is the second of the three Pagan harvest festivals, which include Lammas/Lughnasadh and Samhain.
In Japanese culture the autumn equinox is celebrated with the tradition of Higan, which is a time to remember deceased relatives, as well as mark the passing of the seasons.
Higan lasts for seven days, starting three days before the Equinox and ending three days after it.