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Autumn Equinox 2019: The science behind the changing seasons

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

When leaves begin to fall, temperatures drop and days become shorter, it can only mean autumn is on its way. No matter how hot the summer has been, the next season of the year will soon be upon us with 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 September 23, the date of the Autumn equinox. However under the meteorological definition, which is based on the Gregorian calendar, autumn begins earlier on September 1.

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 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, the autumn equinox takes place on Monday, September 23.

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. In 2019, this happens at 08.50 BST.

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 5 to November 24. 

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 Sunday, October 27.

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.

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 November 3.

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.  

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.  

Many American Halloween traditions have come over to Europe Credit: Susan K/Getty Images

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. 

Thanksgiving, North America

A day spent with family, close friends and a traditional North American feast. Thanksgiving, which falls on November 28 in the United States and October 14 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 

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. 

Credit: Emli Bendixen

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. 

Thai red chicken and pumpkin curry

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

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.