Five things to know about the winter solstice

You can say goodbye to shorter days and start welcoming back more sun as the winter solstice arrives. Winter solstice, marking the day with the fewest hours of daylight in the Northern Hemisphere, takes place this year on December 22 at 4:48 UTC -- that's 11:48 p.m. Eastern time Monday night, December 21.

What causes it?

The astronomical event is caused by Earth's tilt on its axis and continuous orbit around the sun. On this day in the Northern Hemisphere, the sun is at its maximum tilt from the sun (23.5 degrees).

In the Southern Hemisphere, it is the longest day of the year.

What "solstice" means

The word solstice derives from the Latin words sol (sun) and sistere (to stand still), because at the solstice the sun appears to pause at the lowest point in its arc before starting to rise again.

Timing is everything

Although most people think of solstice as the whole day, the winter solstice actually occurs at a specific time. It happens when the sun is directly overhead of the Tropic of Capricorn.

The date can vary

The date of the solstice can vary because of our calendar system. There are 365 days in a typical year and 366 in a leap year. But the solar year, which is the length of time it takes for the sun to appear in the same position from Earth every year, is approximately 365.242199 days. (The length of time can vary based on the positioning of other planets.)

The winter solstice can happen between December 20-23, but usually on December 21 or 22. The last time the solstice took place on December 23 was in 1903.

Cultural observances

Cultures around the world have celebrated the winter solstice for millennia. In Britain, crowds gather to watch the sunrise at Stonehenge as part of a traditional Druid observance of the winter solstice. In ancient times, Romans celebrated Saturnalia, the festival of lights, leading up to the solstice. Some say Saturnalia was a precursor to Christmas.