Winter solstice 2015: Everything you need to know about the shortest day of the year
Today we celebrate the December solstice, marking the longest night and shortest day of the year with the latest dawn and the sun at its lowest point in the sky
The December solstice happens at the same instant for all of us, everywhere on Earth. This year the solstice occurred today Tuesday December 22nd at 04:49 GMT (Universal time) with the sun rising over Stonehenge in Wiltshire at 08:04.
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.
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.
Sunrise between the stones at Stonehenge on the Winter Solstice in 1985 Photo: Mark Grant
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 isn’t the earliest sunset on the year’s shortest day?
Solar noon - the time midway between sunrise and sunset is when the sun reaches its highest point for the day, but the exact time of solar noon, as measured by Earth’s spin, shifts.
A clock ticks off exactly 24 hours from one noon to the next but actual days – as measured by the spin of the Earth – are rarely exactly 24 hours long.
If the Earth’s spin is measured from one solar noon to the next, then one finds that around the time of the December solstice, the time period between consecutive solar noons is actually 30 seconds longer than 24 hours.
Therefore two weeks before the solstice, for example – the sun reaches its 'noontime' position at 11:52 a.m. local standard time.
Two weeks later - on the winter solstice – the sun reached that noontime position at 11:59 a.m. - seven minutes later.
The later clock time for solar noon also means a later clock time for sunrise and sunset. The result? Earlier sunsets before the winter solstice andincreasingly later sunrises for a few weeks after the winter solstice.
The exact date of earliest sunset varies with latitude but the sequence is always the same.
For the Northern Hemisphere the earliest sunset occurs in early December and the latest sunrise in happens in early January.
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.
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).
The sun rises over Salisbury Plain as light illuminates the mist shrouding Stonehenge (Getty)
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.
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.
• Revellers celebrate the 2014 winter solstice at Stonehenge
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.
Arthur Pendragon during the winter solstice at Stonehenge in Wiltshire Photo: PA
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."
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."
Story and photo source: Telegraph By Cameron Macphail
