Winter solstice, shortest day of the year, arrives Thursday evening

On rare occasions, the solstice can happen as early as Dec. 20 or as late as Dec. 23, according to timeanddate.com. To avoid confusion between different time zones, the official time of the solstice is based on Coordinated Universal Time (UTC), which is five hours ahead of Eastern time. By that standard, a Dec. 23 solstice last occurred more than a century ago — in 1903 — and will not happen again until 2303. An early Dec. 20 solstice will happen sooner, in the year 2080.

What is the meaning of the winter solstice?

The December solstice marks the beginning of astronomical winter in the Northern Hemisphere. During the solstice, the noon sun appears directly over the Tropic of Capricorn, a line of latitude 23.5 degrees south of Earth’s equator. It’s the southernmost point at which the sun can be seen straight overhead (90 degrees above the horizon).

In the Northern Hemisphere, we see the sun take its lowest and shortest path across the southern sky. The low sun angle means you will cast your longest midday shadow of the year on the winter solstice, assuming skies are clear.

The word “solstice” comes from the Latin word solstitium, which means “sun standing still.” On the December solstice, the sun’s daily southward movement in the sky appears to pause, and the sun rises and sets at its southernmost points on the horizon. After the solstice, the position of sunrise and sunset shifts northward again and we slowly begin to gain daylight.

Why do we have a solstice?

Solstices and seasons occur because Earth doesn’t orbit the sun completely upright. Instead, Earth’s axis is tilted from the vertical by about 23.5 degrees, which causes each hemisphere to receive different amounts of sunlight throughout the year.

In December, the Northern Hemisphere is tilted away from the sun, bringing us less direct sunlight and colder weather. Meanwhile, in the Southern Hemisphere, Dec. 21 marks the first day of astronomical summer and the longest day of the year. Halfway between the winter and summer solstice are the equinoxes, when the length of day and night are nearly equal everywhere on Earth.

When does winter begin?

Though the winter solstice is often referred to as the “first day of winter,” there are different ways to define the season’s start and end date. Dec. 21 is the first day of astronomical winter in the Northern Hemisphere, which runs until the spring equinox in March. Meteorological winter, however, coincides with the three coldest months of the calendar year, and runs from Dec. 1 to the end of February.

Solar winter, defined as the darkest three-month period of the year, begins in early November and lasts until early February. Many ancient cultures considered the winter solstice to be “midwinter,” as it occurs halfway into the darkest calendar quarter of the year.

When is the shortest day of the year?

The shortest daylight period of the year in the Northern Hemisphere is always on the winter solstice. However, the earliest sunset and latest sunrise of the year do not happen on the same day. D.C. sees 9 hours and 26 minutes of daylight on Dec. 21 (sunrise at 7:23 a.m. and sunset at 4:49 p.m.). The earliest sunset, however, was at 4:45 p.m. on Dec. 7, while the latest sunrise is at 7:27 a.m. on Jan. 5.

The exact dates of the earliest sunset and the latest sunrise depend on one’s latitude. In most of the Lower 48, the earliest sunset and the latest sunrise occur about two weeks before and after the solstice, respectively. Closer to the Arctic Circle, the earliest sunset and latest sunrise occur on or near Dec. 21.

When do the days start getting longer?

Like a swinging pendulum, daylight starts to increase as soon as we get past the solstice, though you probably won’t notice it at first. D.C. gains less than one second of daylight Dec. 22 but gains four seconds of light Dec. 23, according to timeanddate.com. By early January, daylight increases by more than 30 seconds per day.

Cities at higher latitudes closer to the North Pole start gaining sunlight more rapidly. In Anchorage, daylight begins to increase by more than two minutes per day during the first week of January.

How is the winter solstice celebrated?

Humans throughout history have celebrated the solstices with rituals such as bonfires and ceremonial dances to mark the passage of the seasons. The ancient Romans held a week-long pagan festival called Saturnalia, dedicated to the god of time and agriculture, around Dec. 17 to celebrate the return of the sun’s light.

The modern-day association between Christmas and “Yule” comes from the Norse word jól, a pre-Christian winter solstice festival held in Scandinavia. The custom of lighting a Yule log at Christmas is believed to have originated in the bonfires associated with the Feast of Juul, according to timeanddate.com.

Numerous prehistoric monuments and landmarks around the world were built to mark the sun’s changing path in the sky. Stonehenge, which was built more than 5,000 years ago in modern-day England, is perhaps the best known of these prehistoric landmarks. Some historians say the large circle of free-standing stones was once a solar calendar used to track the seasons. Today, thousands gather at Stonehenge each year to celebrate the solstices, equinoxes and the changing of the seasons.