Summer solstice 2018 — here’s what to know about the longest day of the year

Click to play video: 'Thousands gather to celebrate summer solstice at Stonehenge' Thousands gather to celebrate summer solstice at Stonehenge
ABOVE: Thousands of people gathered at Britain's ancient monument Stonehenge on Thursday to celebrate summer solstice – Jun 21, 2018

It’s the longest day of the year for people in the Northern Hemisphere, causing many to mark the summer solstice with pagan rituals, fire dancing and even jumping naked into a lake.

The event may also be a bittersweet feeling for many, as after the summer solstice, the days start getting shorter.

READ MORE: Neo-pagans among thousands to greet summer solstice at Stonehenge

Here’s everything you need to know about the 2018 summer solstice and how people around the world are celebrating.

What is the summer solstice?

Following the winter solstice on Dec. 21, the Northern Hemisphere begins to get more sunlight as the earth’s axis starts slowly tilting more toward the sun.

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The summer solstice happens when the tilt of the Earth’s axis is most inclined towards the sun directly above the Tropic of Cancer.

WATCH: In 2016 the ‘Strawberry’ moon lit up summer solstice for first time in 49 years

Click to play video: '‘Strawberry’ moon lights up summer solstice for 1st time in 49 years' ‘Strawberry’ moon lights up summer solstice for 1st time in 49 years
‘Strawberry’ moon lights up summer solstice for 1st time in 49 years – Jun 21, 2016

During the cosmic event, “the sun shines directly on the Northern Hemisphere and indirectly on the Southern Hemisphere,” NASA explained.

The summer solstice happens every year between June 20 and June 22 when the sun reaches its highest level in North Hemisphere; the exact amount of daylight varies from city to city, but all places north of the equator will have at least 12 hours of daylight.

When is it?

The summer solstice in the northern hemisphere happens June 21, and this year it officially took place at 6:07 am ET.

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What does it have to do with Stonehenge?

The purpose of Stonehenge, which was built around 5,000 years ago, still remains a mystery. However, there are theories that it was designed to align with the sun, according to Salisbury Stonehenge Tours. During the summer solstice, the sun rises over the structure’s Heel Stone and hit the Alter Stone in the centre.

This is why every year thousands of people flock to the prehistoric site to see the sun rise above it.

Thousands of revellers celebrating summer solstice and the dawn of the longest day of the year at Stonehenge this morning on June 21, 2018, in Wiltshire, England. KIRAN RIDLEY / Barcroft Media via Getty Images

Pagan rituals for the summer solstice

In other parts of the world, such as in Europe, people celebrate the event with dancing, eating, drinking and even naked running.

In Russia and Ukraine, it’s a pagan celebration more commonly known as Ivan Kupala Day, which usually takes place shortly after the summer solstice. Teenagers and young adults also jump over bonfires, holding hands with a potential suitor as a courtship ritual.

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READ MORE: 4 things you might not have known about the winter solstice

“If you jump over the fire, and a boy and a girl are holding hands and they’re still holding hands when they’ve jumped over, they’ll get married,” Natalie Kononenko, a professor and the Kule Chair in Ukrainian Ethnography Arts, at the University of Alberta told TIME.

Young women also wear floral wreaths on their heads until later on in the festivities when they take the headpieces off, light candles in them and sail them down a stream.

TOPSHOT – Two girls put traditional wreaths near a bonfire as they take part in the Ivan Kupala Night celebration, a traditional Slavic holiday, outside the small town of Turov, some 270 km south of Minsk, on July 6, 2016. SERGEI GAPON/AFP/Getty Images

Scandinavians celebrate one of their main holidays around the summer solstice, referred to as Midsummer, which has roots in pagan rituals involving bonfires, fertility and folk dancing.

People in Austria light hundreds of fires in the Alps, a medieval tradition to mark the longest day of the year.

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Austria Lower Austria Scheibbs – mid summer festival on the Blassenstein mountain. Hackenberg/ullstein bild via Getty Images

And in Latvia, the summer solstice tradition is to head to the countryside, start a bonfire and stay up all night waiting for the sun to come up. Women pick flowers to make into crowns for their heads, while men are supposed to strip naked and jump into a nearby lake or river, according to the BBC.

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