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Today is the winter solstice and the shortest day of the year in the northern hemisphere.

It also marks the first day of winter from an astronomical point of view with the sun directly overhead the Tropic of Capricorn in the southern hemisphere at 05.30 GMT this morning.

During the winter solstice, the sun is closer to the horizon than at any other time in the year.

A lot of people think the winter solstice is always on December 21 and it often is, but the date does vary. It can occur as early as December 20 and also on December 23 but this is rare.

The last December 23 solstice occurred in 1903 and will not occur again until 2303. The next December 20 solstice will be in 2080.

The date of the summer solstice in June and the winter solstice in December varies mainly because of our modern calendar which does not correspond exactly to the solar year.

The Gregorian calendar consists of 365 days and 366 days in a leap year but the length of time the Earth takes to orbit around the sun is about 365.24 days.

In Antarctica, the penguins may be enjoying the midnight but spare a thought for the polar bears at the North Pole. They won't see the sun for another three months.

For us in Wales, the days will slowly get longer until June 20 2012, the summer solstice. Many people celebrate the winter solstice and in there is festival called "Alban Arthan", Welsh for "Light of Winter.

Today maybe the winter solstice but the weather doesn't seem to know it. In fact it feels more like early spring with temperatures a mild 11 to 13 Celsius but there is a change on the way.

Tomorrow an active cold front will bring a spell of heavy rain followed by brighter weather, a few showers plus a drop in temperature.

Tomorrow night will be much colder than tonight with some ground frost but over Christmas we're still on course for it to turn milder again but windy too.

This is my last blog for 2011 but you can keep up to date with the latest weather news by .

Nadolig Llawen!

Derek