earth and equinox.jpg

Satellite pictures show how sunlight falls on the Earth at different points in the year. The Earth is shown at the winter solstice on Dec. 21, 2010 (upper left), the spring equinox on March 20 (upper right), the summer solstice on June 21, 2011 (lower left), and the fall equinox on Sept. 20, 2011 (lower right). Each image was taken at 6:12 a.m. local time. (NASA)

Monday, Dec. 21, is the official start of winter for many -- the winter solstice. (Meteorological winter began Dec. 1.)

It is also the day that has the shortest daytime and longest night for those in the Northern Hemisphere.

This year's solstice is today at 10:48 p.m. CST. That's the moment when the sun reaches its farthest southward point for the year in the sky, according to EarthSky.org.

A few other things to know about the winter solstice:

(NASA)

*At the winter solstice, the sun shines directly on the Southern Hemisphere and indirectly on the Northern Hemisphere. The winter solstice is the the day in which the Northern Hemisphere gets fewest hours of sunlight during the whole year.

*The December solstice also has the longest daytime of the year in the Southern Hemisphere.

*Every place north of the equator, no matter where, will have fewer than 12 hours of daylight today.

*Daytime lengths vary depending on geographic location. For example, on Dec. 21 Huntsville will have 9 hours, 49 minutes and 32 seconds of daylight. Farther south, in Birmingham, the day length will be 9:55:46; in Mobile it will be 10:09:37.

*After the winter solstice, days in the Northern Hemisphere will progressively get longer. The day length will increase by less than a second on Dec. 22, then each day going forward will add several seconds of daylight.

*Even though today is the shortest day of the year, it's not the earliest sunset. Most places in the U.S. have their earliest sunset a week or so before the solstice and their latest sunrise sometime in January, according to EarthSky.org.

*Because the winter solstice marks when the days begin to lengthen, many cultures celebrate it as a holiday.

*Even though the winter solstice is the shortest day of the year, it won't be the coldest. The coldest period of the season typically comes about 4 to 6 weeks later due to accumulated hemispheric energy loss, according to the National Weather Service.