The Winter Solstice Arrives Today; Here's What That Means

Brian Donegan and Jonathan ErdmanPublished: December 21,2019

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On Saturday, Dec. 21, 2019, the winter solstice marks the official astronomical start of winter in the Northern Hemisphere.

However, many of you already have seen at least some cold and snow for weeks prior to the winter solstice.

(MORE: White Christmas Outlook)

So let's walk through what the winter solstice actually means.

Shown above is the orientation of the Earth relative to the sun's most direct rays around the time of the Northern Hemisphere's winter solstice.

A Tilted Earth Gives Us Our Seasons

Looking from space, the Earth isn't aligned in such a way that a line going through the planet's poles is vertical.

Rather, the Earth has a tilt of roughly 23.5 degrees off a vertical axis.

Because of that tilt, the Northern and Southern hemispheres are tilted either toward or away from the sun at different times of the year as the Earth makes its orbit around its closest star.

Therefore, the most direct sunlight shifts between a band of latitudes, specifically between the Tropic of Cancer and Tropic of Capricorn, throughout the year, leading to the change of seasons seen in the middle and higher latitudes.

The sun's most direct rays are positioned over the Tropic of Capricorn on the Northern Hemisphere's winter solstice.

The Solstice: One Moment in Time

Typically around Dec. 21 or 22 – though on rare occasions, it can be as early as Dec. 20 or as late as Dec. 23 – the sun is directly overhead at the Tropic of Capricorn (23.5 degrees south latitude).

That precise instant in time – in 2019, at 11:19 p.m. EST on Dec. 21 – is the solstice.

Around the time of the winter solstice, the sun is farthest south in the sky at noon in the Northern Hemisphere. Less direct solar radiation means less heating of the ground in the winter hemisphere.

The day of the winter solstice features the least amount of possible daylight hours and the longest night in the Northern Hemisphere. The reverse is true in the Southern Hemisphere.

(MORE: Why Winter Should Really Start on December 1)

Below are some sunrise and sunset times for the winter solstice:

Data: National Weather Service; Table: Infogram

Soon after the winter solstice, the number of daylight hours in the Northern Hemisphere will gradually grow longer each day until the summer solstice in late June, when the greatest amount of daylight hours occurs.

(MORE: How Early the Sun Sets on the Days With Least Daylight Each Year)

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.