The annual pagan celebration, also known as midwinter, signifies the astrological start of the winter in the Northern Hemisphere.  It usually occurs on or around the December 21 of each year. 

The winter solstice takes place when the sun reaches its most southern point over the Tropic of Cancer, which is one of main lines of latitude around the Earth. 

The opposite is true in the Southern Hemisphere where the day is long because the sun will be at its highest point in the sky today.

Why is today the shortest day of the year? 

Unlike our ancestors, we know the astronomical phenomenon not to do with our distance from the sun but the tilt of the earth and how it orbits around the sun.

Earth has a tilt of about 23.5 degrees and as it moves around the Sun, the Northern and Southern hemispheres face opposite directions.

This affects how much warmth and light different places get.

On winter solstice, the Northern Hemisphere is leaning the most away from the sun meaning it receives the least amount of possible daylight hours and the longest night.

When is the shortest day of the year? 

Today is the shortest day with seven hours and 50 minutes of daylight. Sunrise was at 8.03am GMT and sunset is at 3.53pm.

While the cold weather will remain going forward, you should start to notice the days will be longer after December 21.

There may be other subtle changes that you see today during winter solstice, according to astronomical website EarthSky.

EarthSky said: “You might notice how low the sun appears in the sky at local noon. And be sure to look at your noontime shadow. Around the time of the December solstice, it’s your longest noontime shadow of the year.”

Winter solstice has been celebrated for hundreds of years in Britain, pre-dating Christianity.

It was traditionally celebrated by Celtic priests, known as Druids, and each year thousands gather at sacred site Stonehenge to mark the pagan celebration.