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Autumn Equinox 2018: the science behind the changing seasons

Autumn is the perfect time of year to get outdoors and enjoy the changing scenery  - Getty Images Contributor
Autumn is the perfect time of year to get outdoors and enjoy the changing scenery - Getty Images Contributor

Leaves are beginning to drop like the temperature, daylight hours and realisation that another season is upon us. No matter how hot the summer has been, autumn is soon to follow with home comforts, bronzed woodland hues and a pumpkin or two. 

Some say autumn begins on September 23; according to the astronomical calendar the seasonal transition occurs then, on the date of the Autumn equinox. However under the meteorological definition, which is based on the Gregorian calendar, autumn has already begun - on September 1.

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. 

The changing colours also bring joy - however this year that might be more short-lived than usual. After the dry spell over the summer, the usual change in leaf colours will be briefer and browner than last year.  According to the Met Office and Forestry Commission, trees now lack the necessary sugars to make the typical red, yellow and orange that we have come to expect. 

Here is everything you need to know about the third season of the year, from how the equinox works to what you can look forward to over the next few 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's autumn equinox takes place on Sunday, September 23 in 2018.

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 23.5° 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 a little 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. In 2018, this happens at 02.54 UTC (GMT).

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 festival takes place in Alba, Italy, from October 6 to November 25. 

The truffle festival has become one of the biggest cultural events in Northern Italy, and a autumn tradition  - Credit: Christopher Pillitz/Getty
The truffle festival has become one of the biggest cultural events in Northern Italy, and a autumn tradition Credit: Christopher Pillitz/Getty

Thanksgiving, North America

A day spent with family, close friends and a traditional North American feast. Thanksgiving, which falls on November 22 in the United States and October 8 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. 

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. 

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.  

A woman paints a wall in Rajasthan, Inida, during the Diwali celebrations  - Credit: Christophe Boisvieux
A woman paints a wall in Rajasthan, Inida, during the Diwali celebrations Credit: Christophe Boisvieux

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.

Diwali celebrations can be found closer to home, too. This year London's Trafalgar Square will host the annual party of music, dance, yoga, henna art and Indian foods on October 28.

Bonfire Night, UK 

In the UK, November 5 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. 

Halloween 

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

Teenage boy carving pumpkins outdoors - Credit: Moretti/Viant
The event that put pumpkins on the cultural map Credit: Moretti/Viant

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.  

Warming autumn recipes 

Chole chickpea masala

A spiced chickpea dish, partnered with almost-too-hot-to-handle fried bhutara breads. Not only a marvellous crowd-pleaser, but perfect for Diwali celebrations. 

Chole chickpea masala
Chole chickpea masala

Roast pumpkin with burrata and hazelnut pesto

Full of texture and flavour, and a great way to use pumpkin with the perfect ciabatta or sourdough. 

Roast pumpkin with burrata and hazelnut pesto - Credit: Haarala Hamilton
Credit: Haarala Hamilton

Thai red chicken and pumpkin curry

Ginger, garlic and chilli make this curry a warming meal on a cold Autumn night. 

Thai red chicken and pumpkin curry - Credit: Haarala Hamilton
Credit: Haarala Hamilton

Apple and blackberry calzone

An alternative to traditional ­autumn staples such as apple and blackberry crumble,  and delicious served cold or piping hot.

Apple and blackberry calzone
Apple and blackberry calzone