I'm writing this on Monday, December twenty-first, which happens to be the Winter Solstice, the shortest day of the year.

This is the day that the sun turns around in the sky and starts its trek back northwards toward summer, or at least so it seems to those who are thinking in earthbound terms. The change in the amount of daylight is actually a function of the Earth's axial tilt; simply put, in our summer, the northern hemisphere is pointed more toward the sun.

It's summer now in the southern hemisphere, and my daughter's English in-laws know it since they are visiting Australia right now. They are used to the damp if not terribly cold English winters, so are suffering under 95 degree (F) temperatures and lots of sun. I could manage that, but it would be a reach since I'm acclimatized toward winter now.

Interestingly, the Earth's orbit is slightly egg-shaped, and in northern hemisphere winter we are slightly closer to the sun than we are in summer, not that it makes any difference in the temperature.

The amount of daylight we get changes slowly this time of year, but now that the Winter Solstice is out of the way, the days are slowly getting longer, but so little it's hard to tell unless you're a keen observer. In a month the change will come more quickly. By the Vernal Equinox, the first day of spring, the change will amount to several minutes each day.

The shortest day of the year has been important in many cultures and has been for centuries. Stonehenge was probably built to keep track of the solstices and equinoxes, and that was thousands of years ago. There are the remnants of other primitive observatories in many parts of the world, and most were probably used for the same purpose.

Many peoples around the world have celebrations around the Winter Solstice, either on the day or a few days away. Why the fixation on partying in midwinter, anyway? According to historians, it's a natural time for a feast. In an agricultural society, the harvest work is done for the year, and there's nothing left to be done in the fields.

"It's a time when you have some time to devote to your religious life," said Philip Shaw, who researches early Germanic languages and Old English at Leicester University in the U.K, commented on a website. "But also it's a period when, frankly, everyone needs cheering up."

"The dark days that culminate with the shortest day of the year -- the winter solstice -- could be lightened with feasts and decorations. If you happen to live in a region in which midwinter brings striking darkness and cold and hunger, then the urge to have a celebration at the very heart of it to avoid going mad or falling into deep depression is very, very strong," he said.

The celebration in the heart of darkness takes many forms, and Hanukkah and Christmas are the ones we are most familiar with. Some things have changed from the old Pagan days, and others, not so much -- it's a time for banquets, partying, and for many, for celebrating religous tradition.

Some scholars believe that the birth of Christ took place in the spring, and in the early history of the church the celebration of the birth was moved to the Winter Solstice so that people could pay more attention to it -- and to co-opt the traditional pagan Yule holiday and Roman Saturnalia, which took place on the Winter Solstice.

These days the Winter Solstice itself doesn't make all that much different, because you can get rid of the darkness with the flick of an electric light switch. But that doesn't matter, since the winter holiday celebation is still a very powerful season. Behind the Jingle Bells and Christmas sales lies a very powerful tradition that predates the word "Christmas" itself.

Happy Holidays, Merry Christmas, Happy Hanukkah, Spectacular Saturnalia, Cheerful Yule and Warm Solstice to you!