On December 21 at 10:44 UTC ( 3:44 a.m. EST), we experience the shortest period of daylight of the year, which we call Winter Solstice. That means that the northern hemisphere of the earth is more tilted (23 degrees) away from the sun than any other time of the year. Many people believe that the earth is farther away from the sun on December 21st, but this is not true. The distance from the sun is not related to the seasons, since the distance changes over millions of years of time At this particular moment in time, the sun is closer during the winter in the northern hemisphere. If you were living in Australia, the sun would also be closer at this time, but the tilt of the earth in the Southern Hemisphere makes it summer there now.
Although Christians celebrate December 25 as the birthday of Jesus Christ, few claim any knowledge of the exact day he was born. So maybe I have come up with the reason we celebrate Christmas close to the longest, coldest, most depressing night of the year: to help us through the long cold winter! Just think, what is Christmas? This is the time when the days are short and the wind is cold, so why not brighten up the world with Christmas lights and joy? What a great idea! Since people are depressed about the weather and lack of daylight, they may be more prone to buy lots of gifts in an attempt to improve their mood. This will also help the economy by employing lots of people, as shoppers try to cure their Seasonal Affective Disorder (SAD) by spending money.
Throw into this mix the celebration of the New Year seven days later and you have a long length of time to celebrate in all kinds of ways. We surround ourselves with lots of Christmas lights and seasonal joy to help us through this deary time of the year.
So I, in the wake of all this depressing stuff, along with a short earth science lesson, would like to wish everybody a merry Christmas and a happy new year! Oh, yeah, the most important thing is that the days are getting longer now!