The winter solstice happens every year when the Sun reaches its most southerly declination of -23.5 degrees. In other words, when the North Pole is tilted furthest – 23.5 degrees – away from the Sun, delivering the fewest hours of sunlight of the year.
The Sun is directly overhead of the Tropic of Capricorn in the Southern Hemisphere during the December solstice and is closer to the horizon than at any other time in the year, meaning shorter days and longer nights.
The day after the winter solstice marks the beginning of lengthening days, leading up to the summer solstice in June.
In the Southern Hemisphere, it's opposite. Dawn comes early, and dusk comes late. The sun is high and the shortest noontime shadow of the year happens there. In the Southern Hemisphere, people will experience their longest day and shortest night.
What does 'solstice' mean?
The term 'solstice' derives from the Latin word 'solstitium', meaning 'Sun standing still'.
On this day the Sun seems to stand still at the Tropic of Capricorn and then reverses its direction as it reaches its southernmost position as seen from the Earth.
Some prefer the more teutonic term 'sunturn' to descibe the event.
Shouldn't it be on December 21st?
While it more often than not falls on December 21st, the exact time of the solstice varies each year.
Winter Solstice by Barbara Hepworth (1970)
In the Northern hemisphere the winter solstice is the shortest day of the year, because it is tilted away from the sun, and receives the least amount of sunlight on that day.
However, the earliest sunset does not occur on the solstice, because of the slight discrepancy between 'solar time' and the clocks we use.
The shortest day of the year often falls on December 21st, but the modern calendar of 365 days a year - with an extra day every four years - does not correspond exactly to the solar year of 365.2422 days.
The solstice can happen on December 20, 21, 22 or 23, though December 20 or 23 solstices are rare.
The last December 23 solstice was in 1903 and will not happen again until 2303.
Why is Stonehenge important?
Stonehenge, the prehistoric monument located in Wiltshire, is carefully aligned on a sight-line that points to the winter solstice sunset (opposed to New Grange, which points to the winter solstice sunrise, and the Goseck circle, which is aligned to both the sunset and sunrise).
Archaeologists believe it was constructed from 3000 BC to 2000 BC and it is thought that the winter solstice was actually more important to the people who constructed Stonehenge than the Summer solstice.
The winter solstice was a time when cattle was slaughtered (so the animals would not have to be fed during the winter) and the majority of wine and beer was finally fermented.
Sunrise between the stones at Stonehenge on the Winter Solstice in 1985 Photo: Mark Grant
Entrance to the stones is free on December 22nd and will be available from about 7.45am until 10am, when the site will close before re-opening as normal.
The only other megalithic monuments in the British Isles to contain a clear, compelling solar alignment are Newgrange in County Meath, Ireland and Maeshowe situated on Mainland, Orkney, Scotland.
Both famously face the winter solstice sunrise.
Keep up, Druids...
In 2009, a crowd wearing traditional costume, met at Stonehenge on December 21st morning to mark the rising of the sun on the shortest day of the year.
But unfortunately their calculations were slightly out meaning they had in fact arrived 24 hours prematurely.
The '09 solstice fell at exactly 5.47pm that day, and because the sun had already set, the official celebrations should have taken place at sunrise the next day.
English Heritage, who manage the ancient site in Wiltshire, decided to open the gates anyway and welcome those who had made a miscalculation.
A spokesman for English Heritage said at the time: "About 300 people turned up a day early. We took pity on them and opened the stone circle so they could celebrate anyway. They were a day early but no doubt had a wonderful time as well.
"People always assume that because the Summer solstice is the June 21st, the winter solstice will be the 21st December. They should always check because it does change."
Arthur Pendragon during the winter solstice at Stonehenge in Wiltshire Photo: PA
Pagan leader Arthur Pendragon said: "It is the most important day of the year for us because it welcomes in the new sun.
"There were hundreds of people there. If we'd celebrated on the 21st it would have been the right day but the wrong sun – when the whole point of the occasion is about welcoming in the new sun."
The December solstice marks the 'turning of the Sun' as the days slowly get longer. Celebrations of the lighter days to come have been common throughout history with feasts, festivals and holidays around the December solstice celebrated by cultures across the globe.
Ther winter solstice festival Saturnalia began on December 17 and lasted for seven days in In Ancient Rome.
These Saturnalian banquets were held from as far back as around 217 BCE to honor Saturn, the father of the gods.
The holiday was celebrated with a sacrifice at the Temple of Saturn, in the Roman Forum, and a public banquet, followed by private gift-giving, continual partying, and a carnival atmosphere that overturned Roman social norms.
The festival was characterised as a free-for-all when all discipline and orderly behaviour was ignored.
Wars were interrupted or postponed, gambling was permitted, slaves were served by their masters and all grudges and quarrels were forgotten.
Saturnalia by Antoine-Francois Callet (1741-1823) Photo: Oil on canvas. Musée du Louvre
It was traditional to offer gifts of imitation fruit (a symbol of fertility), dolls (symbolic of the custom of human sacrifice), and candles (reminiscent of the bonfires traditionally associated with pagan solstice celebrations).
The Saturnalia would degenerate into a week-long orgy of debauchery and crime – giving rise to the modern use of the term 'saturnalia', meaning a period of unrestrained license and revelry. A mock 'king' was even chosen from a group of slaves or convicts and was allowed to behave as he pleased for seven days (until his eventual ritual execution).
The poet Catullus considered it to be "the best of days."
Feast of Juul
The Feast of Juul (where we get the term 'Yule' from at this time of year) was a pre-Christian festival observed in Scandinavia at the time of the December solstice.
People would light fires to symbolise the heat and light of the returning sun and a Juul (or Yule) log was brought in and dropped in the hearth as a tribute the Norse god Thor.
The Yule Log often was an entire tree, carefully chosen and brought into the house with great ceremony and sometimes, the largest end of the log would be placed into the fire hearth, while the rest of the tree stuck out into the room.
The Yule log is introduced to the proceedings
The log would be lit from the remains of the previous year's log which had been carefully stored away and often slowly fed into the fire through the Twelve Days of Christmas. Tradition dictated that the re-lighting process was carried out by someone with clean hands.
The log was burned until nothing but ash remained. The ashes were then collected and either strewn on the fields as fertilizer every night until Twelfth Night or kept as a charm and or as medicine.
A piece of the log was kept as both a token of good luck and as kindling for the following year’s log.
French peasants believed that if the ashes were kept under the bed, they would protect the house against thunder and lightning. The present-day custom of lighting a Yule log at Christmas is believed to have originated in the bonfires associated with the feast of Juul.
Santo Tomas in Guatemala
December 21 in St Thomas's Day in the Christian calendar. In Guatemala on this day, Mayan Indians indulge in the ritual known as the Palo Volador, or “flying pole dance”.
Three men climb on top of a 50-foot pole as one of them beats a drum and plays a flute. The other two men wind a rope attached to the pole around one foot and jump.
Mayan Indians take part in the Palo Volador in Guatemala Photo: Alamy
If they land on their feet, it is believed that the sun god will be pleased and that the days will start getting longer.
The ancient Incas celebrated a special festival to honour the sun god at the time of the December solstice.
In the 16th century ceremonies were banned by the Roman Catholics in their bid to convert the Inca people to Christianity.
A local group of Quecia Indians in Cusco, Peru, revived the festival in the 1950s. It is now a major festival that begins in Cusco and proceeds to an ancient amphitheatre a few miles away.