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Summer solstice: celebrating the longest day of the year

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From the new-age festivities surrounding England's Stonehenge to the Midsummer's Eve celebrations in Scandinavia, people still gather each year to mark the summer solstice, which officially occurs Saturday, June 21 this year at 6:51 a.m. ET.

Summer solstice campfire celebrations are popular in cooler northern countries like Iceland, Poland, Latvia, Denmark, Sweden and Russia.

While in Canada, Aboriginal Day coincides with the summer solstice. It was selected in 1996 after the Assembly of First Nations called for a day to unite and celebrate native cultures.

The date had meaning because aboriginal societies traditionally marked the summer solstice one way or another.

The Seminole of Oklahoma and New Mexico's Zuni perform corn dances — for rain and the bounty of maize, bean and squash crops. Similarly, Mohawks do Wainodayo, a dance for ripe strawberries, a fruit believed to renew the spirit.

The Dakota hold annual sun dances in North Dakota around the summer solstice, which has been a long tradition of many First Nations from the central North American plains region.

​In some instances, the summer solstice celebrations can court significant controversy.

Residents in a southern Chinese city have come under fire for an annual summer solstice festival in which thousands of dogs are slaughtered for food. So they held their feasts earlier this year to avoid the attention, state media reported earlier this week.

Under the Yulin tradition, eating dog and lychee fruit and drinking liquor on the solstice is supposed to make people stay healthy during winter. It is unclear if the supposed health benefits diminish if the feast occurs before the actual solstice.

Date can vary

The date for the summer solstice can vary from June 20 to 22. But in the Northern Hemisphere in 2014, June 21 is the longest day of the year, as measured in daylight hours.

This year, the solstice occurs at 6:51 a.m. ET, the moment when the Earth's access is tilted most toward the sun, ushering in the official arrival of summer.

The solstice — derived from the Latin words sol (sun) and sistere (stand still) — results from the 23.5-degree tilt in the Earth's axis as it orbits the sun. 

Although the arrival of the summer solstice cannot be seen per se, it is the time when the North Pole is tilted as much as it can possibly be toward the sun, which is directly above the Tropic of Cancer.

When the winter solstice occurs, around Dec. 21, the tilt is as much as possible in the opposite direction and the sun is directly above the Tropic of Capricorn.

In the Southern Hemisphere, the summer solstice is usually celebrated on or around Dec. 21.

Astronomy at work

Astronomical factors and the need for a leap year every four years play into the exact timing of the solstice.

"A year of 365 days is only how we humans have chosen to divide time into convenient chunks," Somak Raychaudhury, a reader in astrophysics at Birmingham University in the U.K., told the BBC.

While we commonly think of a year as 365 days, its average duration is actually 365 days, five hours, 48 minutes and 45 seconds, Raychaudhury said, creating a situation that effectively pushes the solstice six hours later each year, and leads to the addition of an extra day to the end of February every four years.

"This makes the June solstice jump back to the previous date for each leap year," said Raychaudhury

While some may not think of the solstice as a cause for celebration, it is a day of deep historical and cultural significance.

Solstice celebrations were a highlight of the pre-Christian calendar, and bonfires, maypole dances and courtship rituals linger on in many countries as holdovers from Europe's pagan past.

One British landmark has become a particularly popular solstice party destination, with as many as 30,000 people, including hippies, ravers and modern Druids, waiting there some years for the sunrise on solstice morning.

"Stonehenge is an ancient prehistoric site and has been a place of worship and celebration at the time of summer solstice since time immemorial," English Heritage, the monument's caretaker, says on its website.

But the celebrations at the World Heritage Site can also attract their share of troublemakers. Police closed the site in 1984 after repeated clashes with revellers. English Heritage began allowing full access to the Stonehenge again in 2000.

This year, the site in Wiltshire will be closed to visitors later on Saturday "to clear up" after the summer solstice, English Heritage said.