Winter Solstice 2011 begins Dec. 21-22, but many in the Northern Hemisphere, who regard it as the start of winter, don't actually know where the idea of solstice came from, much less what time it begins for them and what the tradition actually means.

Below, scroll through a rundown of the major facts to know about Winter Solstice 2011, from when it begins around the world to how the solstice traditions got started.

What is the Winter Solstice?

In scientific terms, the Winter Solstice is when the earth's axial tilt of the polar hemisphere (aka the North Pole) is tiltest farthest from the sun, roughly 23.5 degrees away. For the northern hemisphere, the winter solstice occurs around Dec. 20 (on Dec. 22 for most this year) and happens six month later for the southern, when it's called the Southern Solstice.

What does that mean for me?

The start of the Winter Solstice marks the shortest day and the longest night of any given year. Once the solstice begins, nights will get shorter and days will get longer, which also means the days will seem a bit dark at first, especially for those further north. When the Summer Solstice occurs in June, the days will begin to get shorter again.

For many, Winter Solstice 2011 signals the beginning of winter as well as a symbolic returning of light into the world. the Talmud recognizes the Winter Solstice as Tekufat Tevet, and in China the Dongzhi Festival is celebrated as a solstice rite.

When is the Winter Solstice?

In the U.S., the Winter Solstice begins 12:30am EST on Dec. 22, and Americans can calculate when the solstice will begin for them from there. Because of time differences, some states and nations will begin Winter Solstice 2011 on Dec. 21 instead.

To calculate when the solstice begins for you, check out the Event Time Announcer and scroll down to the closest city.

How Did the Winter Solstice Tradition Begin?

The solstice played a huge role in ancient cultures, and the word itself is Latin for sun stand-still.

In ancient Rome, the Winter Solstice was celebrated at the feast of Saturnalia to honor the king of the gods (many rituals were later absorbed into Christmas traditions), and pre-Christian Scandanavia would hold the Feast of Juul, known today as the Yuletide celebrations that span 12 days at the end of December.

One of the most famous celebrations of the Winter Solstice today also follows an ancient tradition, that of the Celts.Thousands of druids and pagans gather each year even into 2011 to chant, dance and sing in anticipation of the first winter sunrise.