for National Geographic News
The winter solstice is again upon the Northern Hemisphere, and though the year's shortest day heralds the onset of winter it also promises the gradual return of the sun after a prolonged period of darkness.
That there are holidays at the time of this astronomical event is no coincidence. Since ancient times, people have celebrated the solstice and observed it with many different cultural and religious traditions. Some of them survive to the present daythough not always in the form you might expect.
In the Northern Hemisphere, the winter solstice always occurs on or about December 21 and marks the beginning of the winter season. As many people notice, it's the shortest day of the year, featuring the least amount of daylight between sunrise and sunset.
In the Southern Hemisphere, this is the time of the summer solstice and the longest day of the year. From now on, as the northern days grow longer so do the southern days get shorter.
The term solstice means "sun stands still." On the year's two solstices (winter and summer) the sun appears to halt in its incremental journey across the sky and change little in position during this time. Of course, contrary to appearances from Earth, the sun's "changing position" throughout the year is actually caused by the rotation of the Earth on its tilted axis as it circles the sun each year.
The solstice occurs twice a year (around December 22nd and June 21st) when the sun is farthest from the tilting planet's celestial equator.
For half of each year the North Pole is tilted toward the sun, and for half of the year the South Pole enjoys that privilege. This phenomenon creates our changing seasons, because the hemisphere facing the sun receives longer and more powerful exposure to sunlight.
In the Northern Hemisphere, the winter solstice occurs in December when the tilting of the earth makes the sun appear to be furthest to the south and furthest away. In the Southern Hemisphere, both the seasons and solstices are reversed.
Winter Solstice Has Been Celebrated Since Ancient Times
The holiday timing of the winter solstice is rooted in ancient religions. Throughout history, humans have observed this seasonal milestone and created spiritual and cultural traditions to celebrate the rebirth of sunlight after the darkest period of the year.
Modern pagans attempt to observe the solstice in the traditional manner of the ancients. "There is a resurgent interest in more traditional religious groups that is often driven by ecological motives," said Harry Yeide, a professor of religion at George Washington University. "These people do celebrate the solstice itself."