Winter officially begins on Dec. 21, marking the slow return of the sun making the days become longer for those north of the equator. The day itself is the darkest and shortest day of the year, when the sun reaches its southernmost point in the sky.

For those unfamiliar with the event, below are five answers to common questions about the Winter Solstice.

When does the Winter Solstice begin?

The Winter Solstice begins Dec. 21, 2013, at 5:11 Coordinated Universal Time or 12:11 p.m. Eastern time. On that day, the continental United States will receive nine hours and 32 minutes of daylight.

Why does the solstice occur?

The solstice occurs due to the Earth’s axis of rotation, which for the Winter Solstice in the Northern Hemisphere, is faced the furthest away from the sun. At this time, the sun is at the southernmost point in the sky -- 23.5 degrees south of the celestial equator known as the Tropic of Cancer.

How is the solstice celebrated?

The word “solstice” comes from the Latin words “sol” for sun and “sisto” for “stop.” On Dec. 21, the sun will stop moving southward, pause and begin moving northward. The date has held special meaning throughout history.

"Culturally, the solstices and equinoxes are typically used to denote either the beginnings of the seasons or the center points of the seasons," as in England, Rick Kline, of the Spacecraft Planetary Imaging Facility at Cornell University in Ithaca, N.Y., tells USA Today. "Christmas, Hanukkah, Kwanzaa and other holidays have arisen out of the solstices, equinoxes and the midpoints between them."

Other traditions see the Winter Solstice as the turning point in the year. It's a "cosmological crisis point, in which the outcome of the coming year would be determined," Edwin Krupp, director of the Griffith Observatory in Los Angeles, says.

How is Christmas tied to the Winter Solstice?

Long before there was a man called Jesus, the winter solstice was celebrated as a the return of the sun. In Scandanavia, the time would be marked by burning large logs -- believing that each spark from the fire would represent a new pig or calf in the new year. In Rome, early Romans observed Saturnalia, a holiday in honor of Saturn, the god of agriculture, and Juvenalia, a feast honoring the children of Rome.

The early Christian Church decided to “adopt” Dec. 25 as the day to celebrate the birth of Christ in an effort to absorb the pagan celebrations and popularize the holiday.

"First, we don't really know when Christ was born, it's that simple," Krupp says. "It had its antecedents in Rome, which already had a celebration called Dies Natalis Solis Invictus, the Birthday of the Unconquerable Sun."

Is it the coldest day of the year?

While the it may be the day where the Northern Hemisphere is furthest away from the sun, that doesn't necessarily make it the coldest day of the year. There's a “lag” between the shortest day and the coldest temperature, according to the National Weather Service.

“This lag in temperature occurs because even though the minutes of daylight are increasing, the earth's surface continues to lose more energy than it receives from the sun,” the weather service explains on its website.

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