Autumn Equinox 2021: the science behind the changing seasons

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When does autumn begin, and what happens during the equinox?

Autumn Equinox 2021: the science behind the changing seasons
Autumn Equinox uk 2021 science behind changing seasons
Autumn brings with it with it home comforts, bronzed woodland hues and a pumpkin or two

When leaves begin to fall, temperatures drop and days become shorter, it can only mean autumn is on its way and brings with it home comforts, bronzed woodland hues and a pumpkin or two. 

For many, autumn is enjoyable because of its festivals and the sense that “life starts all over again when it gets crisp in the fall”, if you’re of the same opinion as F. Scott Fitzgerald. 

According to the astronomical calendar, the seasonal transition occurs on 22 September, the date of the Autumn equinox. However under the meteorological definition, which is based on the Gregorian calendar, autumn began on 1 September.

Here is everything you need to know about the changing seasons, from how the equinox works to what you can look forward to over the coming months.

Why is it called the autumn ‘equinox’?

Since night and day are nearly exactly the same length – 12 hours – all over the world the event is called the equinox, which literally means ‘equal night’ in Latin (equi – equal, and nox – night).

In reality though, equinoxes do not have exactly 12 hours of daylight. Solstices and equinoxes mark key stages in the astronomical cycle of the earth. In a year there are two equinoxes (spring and autumn) and two solstices (summer and winter).

This year, the autumn equinox takes place on Wednesday, 22 September.

The dates of the equinoxes and solstices aren’t fixed due to the Earth’s elliptical orbit of the sun. They are closest in January, and most distant in July (aphelion).

The equinox marks the change of seasons, as the balance of light shifts to make for longer days or nights. Whether that means snow storms or heat waves depends on the hemisphere. 

It is also possible to see the Sun rising and setting directly in the East and West, whereas it appears off-centre at other times of year.   

What happens on an equinox?

The Earth’s axis always tilts at an angle of about 23.4° in relation to the ecliptic, i.e the imaginary plane created by the Earth’s orbit around the Sun.

On any other day of the year, either the Northern Hemisphere or the Southern Hemisphere tilts slightly towards the Sun but on the two equinoxes, the tilt of the Earth’s axis is perpendicular to the Sun’s rays.

The equinox occurs at the exact moment the Sun crosses the celestial equator – the imaginary line in the sky above the Earth’s Equator – from south to north.

At this moment, the Earth’s axis is neither tilted away from nor towards the Sun. 

Autumn festivals around the world

With a new season comes an excuse for celebration – here’s our guide to the festivals most associated with autumn around the world.

Alba White Truffle Festival, Italy

In Piedmont, the season of harvest brings thousands of visitors to the International Alba White Truffle Festival – Fiera Internazionale del Tartufo Bianco d’Alba – hoping to purchase and sample the local delicacy from local farmers. 

There’s music, cultural events and markets providing a feast of local food and wine, as well as the famous white truffle that grow among the poplar trees in the hills of this northern Italian region. 

This year’s fair is scheduled to take place in Alba, Italy, from 9 October to 5 December. 

Truffle festival cultural events Italy autumn tradition equinox seasons european celebrations
The truffle festival has become one of the biggest cultural events in Northern Italy, and a autumn tradition CREDIT: Christopher Pillitz/Getty Images

Diwali, India

This festival sees fireworks, lights and feasting take place across the Hindu, Sikh, and Buddhist world, upon the new moon that falls at the end of October or early November. This year’s celebration falls on Thursday, 4 November. 

Oil lamp decorations burn in the streets, creating an atmospheric nighttime spectacle. In fact, the word ‘Diwali’ means “rows of lighted lamps” in Sanskrit, an ancient Indian language.  

For Indians, this national holiday commemorates the return of Ram, the lord of virtue. It also marks the end of harvest season, so prayers of thanks are also given to Lakshmi, the Hindu goddess of wealth and prosperity.


This is perhaps the event that put pumpkins on the cultural map: Halloween is celebrated on 31 October with traditions new and old, such as fancy dress parties, trick-or-treating, and pumpkin carving.  

Though now associated with Americanisation, the traditions of Halloween are thought to have begun in Celtic Britain. The event has two rumoured origins: either as a Pagan festival celebrating the end of harvest or the Christian feast of All Hallows.

The celebration has been particularly popular with children over the last century, when many American traditions such as pumpkin carving came to Europe.  

Two girls and a boy are playing in the woods, covering their faces with carved halloween pumpkins
Many US Halloween traditions have come over to Europe CREDIT: Susan K/Getty Images

Bonfire Night, UK 

In the UK, 5 November marks the day that Guido Fawkes attempted to blow up Parliament in 1605, in the famous Gunpowder Plot. 

On that date, Londoners lit bonfires in celebration of the failed plot, and so in 1606 the 5th November Act was passed to ensure a public holiday in celebration of the fact.  

Although bonfire night traditions have changed over the years, many people still gather for public firework displays and events such as the Lewes Bonfire, Sussex: the largest event of its kind, which sees a torch-lit parade and the burning of famous effigies. 

Thanksgiving, North America

A day spent with family, close friends and a traditional North American feast. Thanksgiving, which falls on 25 November in the United States and 11 October in Canada this year, became a holiday centered on coming together around the time of harvest and remains much the same today. 

In the United States, the first feast between Plymouth colonists and Wampanoag Indians took place in 1621, while in Canada the first ‘Thanksgiving’ took place as early as 1578 after the Englishman Martin Frobisher returned from exploring the Northwest Passage. 

Some of the most well-known Thanksgiving spectacles include the Macy parade in New York and the Canadian Football League’s ‘Thanksgiving Day Classic’. 

In the States, the November holiday comes a day before the Black Friday sale, marking the beginning of the Christmas shopping season. 

Warming autumn recipes

Chicken and leek pie with cheddar hazelnut crumble recipe

This is a chicken pie with a difference. The creamy chicken and leek filling is topped with a gorgeous cheesy, nutty crumble instead of pastry – a luxurious take on an old favourite.  

warming autumn recipes chicken and leek pie equinox 2021 uk
Chicken and leek pie with cheddar hazelnut crumble

Saag halloumi (spiced spinach with halloumi) recipe

This is based on the classic British-Indian staple of saag paneer, though with a little more emphasis on lightness and freshness. This home version uses halloumi instead of paneer – which allows the saltiness of halloumi brings out so much more character in the spices.

Tomato and tapenade tart recipe

This tart is very simple. It calls for excellent tomatoes – heavy, deep-coloured bull’s hearts if you can get them, and a few yellow and red plum ones to fill in the gaps. Tapenade is one of the world’s best savoury pastes – a thin spread under the tomatoes goes a long way.

warming autumn recipes tomato tart equinox 2021 uk
Tomato and tapenade tart

Banana chocolate muffins recipe

If you are looking for a quick, no-faff, healthy baked treat, these could be your answer. They have a rich chocolateyness, but the banana flavour reveals its healthy credentials. The building blocks for these cakes are not just butter and sugar, but banana, sweet potato, yogurt, olive oil and cooked quinoa. 

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