Winter solstice

Winter solstice is a term used for an astronomical event that marks the shortest day of the year. It is the day when an area of Earth receives the fewest hours of daylight and winter begins. Solstices are determined by the position of Earth’s axis in relation to the sun. There are two winter solstices each year, one in the Northern Hemisphere and one in the Southern Hemisphere. As far back as prehistoric times, solstices were commemorated with festivals and celebrations. In contemporary times, people often continue these commemorations by traveling to one of the sites where ancient people are believed to have marked the solstice.

Background

The word solstice comes from the Latin words sol, which means “sun,” and stitium, which means “stoppage.” Together, the word solstitium refers to the day when the light from the sun appears to be cut short. The solstice marks the point when the hours of daylight are at the absolute minimum. After the passage of the solstice, the hours of daylight gradually increase.

The seasons are determined by the position of Earth in relation to the sun. The planet revolves around an imaginary axis that ends in the North and South Poles. This axis is tilted at an angle of 23.4 degrees from Earth’s orbit, or path, around the sun. This tilt means that different parts of the planet get different amounts of sunlight at different times in Earth’s orbit around the sun, which takes a year. This alters the temperature and other weather conditions and is the cause of Earth’s seasons.

Earth is divided in half by an imaginary line that stretches around the planet at its midpoint. This is called the equator, from the Latin aequare, meaning “make equal.” This line theoretically divides Earth into two equal halves known as the Northern and Southern Hemispheres. For part of the year, the Northern Hemisphere is closer to the sun and experiences warmer weather, while the Southern Hemisphere is farther away and experiences the colder seasons. The rest of the year, the angle of Earth towards the sun changes, causing the Northern Hemisphere to experience colder weather while the Southern Hemisphere receives more sun and warmer weather.

There are other imaginary lines that also have an influence on Earth’s climate. These are lines of latitude, which run parallel to the equator and surround Earth. The lines are numbered, with the equator being designated as 0 and the lines nearest the poles being labeled as 90 for those closest to the North Pole and -90 for those closest to the South Pole.

Because Earth is tilted at a 23.4–degree angle to the sun, the lines of latitude at 23.4 degrees and -23.4 degrees line up directly under the sun at noon on specific days during the year. The line is called the Tropic of Cancer in the Northern Hemisphere and the Tropic of Capricorn in the Southern Hemisphere. The sun is directly over the Tropic of Cancer in the Northern Hemisphere in June, and the day is known as the June solstice. In the Southern Hemisphere, the Tropic of Capricorn lines up with the sun in December; this is known as the December solstice. These solstices mark the point of the longest day of daylight in each area.

In the Northern Hemisphere, the solstice that occurs in December is known as the winter solstice; in the Southern Hemisphere, the same day is known as the summer solstice. Likewise, the June solstice is known as the winter solstice in the Southern Hemisphere and the December solstice is the summer solstice. The exact day varies, with the December solstice landing between December 20 and 23 and the June solstice occurring between June 20 and 23. However, the solstices most commonly occur on December 21 and June 21, respectively.

The solstice actually occurs at a specific moment in time, marked by the exact instant the appropriate pole is tilted at the 23.4–degree mark from the sun. This time is officially recorded in Coordinated Universal Time, or UTC. Each area determines the exact time of the solstice by converting the appropriate UTC time to the time for the local time zone. This is because the solstice occurs at the exact same instant all around the world.

Overview

The winter solstice has long held significance for humankind. Ancient people are known to have seen it as a time representing death and rebirth because it was the point at which the days were shortest and then began lengthening. The realization that the days were getting shorter was frightening to the ancient people, who had little understanding of Earth’s relationship to the sun. They feared that the sun would not return, and would mean no light, heat, or food. This is why many celebrations of the solstice include the use of fire, as a way of honoring the light and inviting its return.

Many ancient monuments appear to be aligned to recognize the winter solstice. These include Stonehenge on the Salisbury plain in England, Newgrange in Ireland, and Machu Picchu in Peru. Sections of these monuments align directly with where the sun appears at the moment of the solstice, and may have been important gathering sites for people in ancient times. In contemporary times, many people gather at these sites to mark the solstice. In some cases, lotteries are held to select those who will be able to be present at the moment of the solstice because the demand is so great.

Other cultures also put special emphasis on the time of the solstice. For instance, in ancient Rome, midwinter festivals called Saturnalia after Saturn, the god of agriculture, were held that corresponded with the solstice. Some experts believe that these celebrations are also the reason the Christian holiday of Christmas is held in December instead of in springtime, when conditions would have been more in keeping with the events described in the Bible. Experts theorize the birthday of Jesus Christ was assigned a date in December to replace the pagan solstice festivals and make it easier for ancient people to accept new beliefs.

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