Happy Winter Solstice to all Earthlings!

The year is 2007 AD. My calendar reads December 21, the special date called Winter Solstice. Or Summer Solstice south of the equator.

The solstices and the equinoxes each mark the beginning of the four seasons. There is a Summer and a Winter Solstice. And there are two equinoxes as well (Spring and Autumn).

So what is Winter Solstice? It's the day on which Winter season starts in the northern hemisphere (and Summer starts below the equator).

And it's also the shortest day/longest night of the year north of the equator (or the longest day in the southern hemisphere).

Solstice was known as a special moment of the year since Neolithic times, as is confirmed by archaeological sites such as Stonehenge.

Many cultures celebrate the Winter and Summer solstices, the equinoxes, and even the midpoints between them, leading to LOTS and LOTS of holidays!

So many holidays around the world are linked to the winter solstice.

Christmas is the most popular midwinter celebration. The birth of Christ is observed on December 25th, since that was the winter Solstice when the Julian Calendar was created way back in 45 BC.

So why two solstices per year? Because the Earth's axis tilting furthest from or toward the Sun causes the Sun to be farthest north or south at noon.

It must be really amazing to witness the Winter solstice in places way up north in the Arctic Circle, where you see the Sun above the horizon the entire day! They call that the midnight sun (or midsummer-night sun or polar day). And the reverse happens down south in the Antarctic Circle - the Sun never even comes up at all. That is the polar night. And by now you surely guessed that during the Summer solstice the effects on both hemispheres are just the opposite.

Here's something that not everyone knows... the seasons are NOT caused by Earth being cloeser or farther from the Sun. The orbital eccentricity of the Earth's orbit does make a small contribution, but the main reason is because of Earth's tilt!

Oh, did I mention my favorite reason for celebrating Winter Solstice? Simple, the days are getting longer again (here in the northern hemisphere). That's right, for the next six months we get a bit more sunlight every day.

So have a happy Winter Solstice! And even if you are covered in snow and the skies are grey, rest assured the turning point has been reached. Out with the old, in with the new!