What’s a Solstice?
This June 20th at 659 PM CDT marked the arrival of the Summer Solstice, most commonly referred to as the longest day of the year for us living on the Northern Hemisphere. We’ve been gaining daylight since December 22nd of last year. You remember that day, right? We called it the Winter Solstice, or shortest day of the year. So what is a Solstice anyway?
Literally Solstice comes to us from Latin where Sol is the sun and Sistere means to stand still. What it refers to is the oscillation that the sun makes through the year between its northern-most point to its southern-most point in the sky and back again. If you observe either the sunrise or sunset over a year’s time, you will find that the sun will rise or set at progressively different points on the horizon. At one point, it will stop its progression to the north or south and start a progression in the opposite direction. The point at which the sun stops, or stands still, only to reverse its course is called the Solstice. Its farthest point south is the Winter Solstice. This is characterized by its low path across the sky to the south. This low journey above the horizon is also a short trip, accounting for short days, long nights, and progressively colder average temperatures. The farthest point north then is the Summer Solstice where the sun is high in the sky and the days are long and warm. There are a few celestial motions involved that explain these apparent solar wanderings. These motions are rather simple once you construct the picture. Refer to the image below. The consequences of these motions account for the change in seasons and the varying types of weather we incur throughout the year.
.jpg)
I believe everyone knows that planet Earth spins like a top, alternating between day and night, and making a
complete spin in 24 hours. During the day, land masses will readily absorb heat from the sun and radiate much
of that heat back into space at night. If days are longer than night, we build up a resource of heat, gaining more
in the day than losing during the night. As days lose time to night, approaching the Winter Solstice, land masses
radiate more heat than they gain. Now this top that we live on leans in one direction while it spins. It leans at a 23.5
degree angle from the vertical. All the while that it’s spinning daily at this angle, the earth also makes a near circular
trip around the sun, completing this trip in 365 days. At one point in this circle, the Northern Hemisphere is leaning
away from the sun at 23.5 degrees. Halfway around the circle from that point, it will be leaning toward the sun at that
same 23.5 degrees. This latter position is the Summer Solstice. Leaning toward the sun exposes us to a high
incidence of solar radiation within a relatively long time span when compared to the shorter nighttime cooling
period. After the Summer Solstice this month, we end our sojourn toward summer and begin moving toward
winter again. This will take a while. So there’s plenty of summer to enjoy yet.
As an added note, these circles of latitude at 23.5 degrees north and south of the equator are referred to the Tropics of Cancer and Capricorn, respectively. You may have seen these annotated on your globe or in the atlas and can now question their significance no longer.
Return to News Archive
