First Day of Winter

Yesterday was the Winter Solstice in the Northern Hemisphere--the shortest day of the year and the beginning of winter.

From June to December, the days gradually grow shorter until the far North falls into the complete darkness of winter. At the Winter Solstice, the point during the year when the Northern Hemisphere is most inclined from the Sun, this trend reverses and the days begin to lengthen.  

On Winter Solstice, the polar North receives no energy from the Sun, a contrast to Summer Solstice, when the North Pole receives 30 percent more solar energy than the Equator. This images show the amount of sunlight that is reflected from the Earth during Winter Solstice 2004 as measured by the CERES instrument on NASA's Terra satellite. The far North is dark blue, indicating that no sunlight is being reflected back into space.

The most sunlight is being reflected out of the Southern Hemisphere, where December 22 marked the longest day of the year. The Southern Hemisphere reflects so much light because Antarctica is nearly entirely covered in bright white snow, which reflects light well. Bright white clouds also stand out because they are reflecting so much light back into space.

--Bjorn Carey

Amazing Images: Science & Nature Photos from Our Readers

Credit: CERES Science Team at NASA Langley Research Center