Winter solstice: What is it?

Last updated at 11:12
Mountain sunshineGetty Images

On Friday 21 December the northern hemisphere experiences something called the Winter solstice.

The date marks the 24-hour period with the fewest hours of daylight in the year, which is why it is known as the shortest day and longest night.

So what's the science behind it?

It happens because at this particular moment the North Pole is tilted furthest away from the sun as the Earth continues on its orbit - which is why it's winter in the Northern hemisphere at this time of the year

In the southern hemisphere it's exactly the opposite story - the South Pole is pointing towards the Sun, making it summertime 'down-under'.

Summer Winter Solstice ChartGetty Images

In Sydney, Australia, they're having their summer solstice - mornings will start getting darker from the middle of December, and evenings will get lighter until early January.

But in the UK (and rest of the northern hemisphere) it means the sun rising earlier and setting later as we journey again towards the spring equinox.

Vector diagram illustrating Earth seasons. equinoxes and solsticesGetty Images

But even though this is the point with the least hours of daylight, it's not the earliest sunset of the year, or the latest sunrise.

The mornings continue darkening until early in the new year.

The reason why is that a day - a solar day that is - is not always exactly 24 hours.

Winter Solstice has been celebrated in cultures the world over for thousands of years.

In the olden days it was known as Yule, and was a celebration of light and the rebirth of the Sun.

'Yule' is still celebrated in Germany and Scandinavia, and this is where we get many many of our Christmas customs, including Christmas trees and putting wreaths on the front door.

Thousands of people gathered at Stonehenge in Wiltshire to watch the sun rise on the shortest day of the year.Getty Images
UK: Thousands of people gather at Stonehenge in Wiltshire to watch the sun rise on the shortest day of the year
Visitors attend the Firewalking Winter Solstice event in Baltezers, Latvia, 15 December 2018EPA
LATVIA: Visitors attend the Fire walking Winter Solstice event in Baltezers
People lighting a lanternGetty Images
CANADA: In Vancouver a special Winter Solstice Lantern Festival is held every year
Rice balls called tang yuan.Getty Images
CHINA: The Winter solstice marks the end of the harvest season and is celebrated with family gatherings and a big meal, including rice balls called tang yuan.

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