The Nature of Winter Solstice
by Suzanne Petersen, education specialist
Lamprey River Advisory Committee
What does solstice mean?
Solstice comes from two Latin words, “sol”, meaning sun, and “stitium” meaning pause or stop. Solstice is commonly understood as the day when the length of day is shortest (winter solstice) or longest (summer solstice). It is also recognized as the first day of winter or summer, respectively. The winter solstice usually occurs December 21 or 22.
Every day, the Earth spins on its axis and makes a full rotation. Day length is based on how long a certain location receives the sun’s rays. If the Earth were to rotate around a vertical axis, every day almost every place on earth would have twelve hours of light and twelve hours of dark. Just as a classroom globe is tilted on its axis, the real Earth is also tilted on its axis. The angle of this tilt is 23.5 degrees off horizontal. Because of this tilt, day length varies over the course of a year.
Each year, the Earth makes a full revolution around the sun. The tilt of the Earth, regardless of time of year, is always 23.5 degrees and the north axis always points to the north. Imagine holding the globe, with the base flat on your hands, revolving around your house, the sun. As you walk, you must always keep the North Pole pointing north. When you are south of the house, the North Pole will point toward the house. When you are north of the house, the South Pole will point toward the house.
WINTER SOLSTICE DIAGRAM HERE
(Winter solstice. The sun in this illustration is much smaller and closer than reality, but it does show that at the Tropic of Capricorn, the sun’s rays hit the earth at a perpendicular angle during winter solstice. The rays hitting elsewhere do so at an angle, and the sun’s energy is less intense. Note that points north of the Arctic Circle get no sun at all.)
In the winter, the northern hemisphere points away from the sun and the southern hemisphere points toward the sun. In the north, days become shorter. The sun’s daily course across the sky is low, creating long shadows. At points north of the Arctic Circle, the days become so short that there is hardly any day light, and the sun barely rises above the horizon. In the northern hemisphere, winter solstice is the extreme of these conditions. The length of day is the shortest and the length of night is longest. For a person standing outside at noon, the shadow will be longer than at any other noon during the year. Above the Arctic Circle, the sun does not rise at all and there is only the darkness of night.
Scientists can define the exact moment of the winter solstice, but to do so, they must look to the southern hemisphere. The winter solstice occurs when the sun’s angle is exactly 90 degrees at noon somewhere along the Tropic of Capricorn (23.5 degrees south of the Equator). When this happens, a straight pole erected there will cast no shadow at all. In terms of Earth’s daily rotation, the Earth does not stand still. In terms of the Earth’s revolution, however, the Earth does "stand still", for just a moment. At that moment, the North Pole is pointing as far north and away from the sun as is possible. After that moment, the earth begins its journey back around the sun and the sun’s reach in the north gradually increases. Before the winter solstice, day length in the north gets slightly shorter each day. After the winter solstice, day length gets slightly longer each day. As the sun’s position in the sky gets higher, the Earth receives more direct radiation from the sun, and, therefore, greater warmth.
What Does the Winter Solstice Mean for Nature?
Nature does not note the solstice as such. One might think that the winter solstice would mark the coldest day of the year, because it is the darkest day of the year. That, however, is not true. Just as humans mark the winter solstice as the first official day of winter, the solstice for nature is just a beginning. After the solstice, days get a bit longer and the sun shines more directly, but the earth is so big that there is a lag between the amount of sunshine and warmth. The peak of cold winter weather usually comes about halfway through winter, from late January into mid-February.
What Does the Winter Solstice Mean for People?
People in the northern hemisphere have long had customs to mark and celebrate the winter solstice. Most cultures recognize the significance of the longest night that will yield to increasing daylight. They know that the darkness and cold can be dreary, and even difficult to survive. The winter solstice is recognized as an opportunity to celebrate the beginning to a return of light and eventual warmth, even though spring will not actually come for a few more months. Many late December festivities make use of candle light, feasts, singing and dancing, and opportunities to start fresh. Let us all join in a celebration of the longest night and the beginning of winter. Remember that the days will again get longer and that darkness will not rule the day.
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