It is a time of year in the Northern Hemisphere that marks the return of the sun as the days lengthen and summer approaches.

Anthropologists hypothesize the discovery of the solstice occurred back around 5000 BC with the Mesopotamians.

The ancient culture would celebrate with a 12-day festival designed to help the god Marduk tame the monsters of chaos for another year.

Traditionally, winter solstice is celebrated on or about Dec. 21, which has long been regarded as the shortest day of the year (the winter solstice this year is Saturday at 6:14 p.m.).

Scientifically, the shortest day of the year does not necessarily occur right on the winter solstice.

In fact, the date of the "shortest day of the year" can vary, depending on your latitude. The science surrounding the phenomenon is a little complicated. And, unless you are planning a major in physics or are an astronomy buff, the explanation would likely put an insomniac to sleep. But for the sake of clarity, let's attempt to simplify the explanation.

The longest and shortest days of the year, depending on the season, occur in relation to the Earth's elliptical orbit around the sun and the tilt of the Earth's axis along its orbital plane.

For the solstice to occur on the same day every year the speed of the Earth's orbit would have to be constant. Due to the elliptical orbit of the Earth during certain months, as the Earth moves closer to the sun, the speed of the orbit is altered.

The closer to the equator the earlier the shortest or longest days occur; the farther north the later.

At timeanddate.com, a world clock can demonstrate the shortening of the days.

Here in Yellowknife the shortest day of the year is actually Friday. In Calgary, the shortest day of the year will be Thursday.