We define a year as the time it takes the Earth to complete one orbit around the Sun. Another way of defining a year is measuring the time it takes for the sun to reach certain points in the sky with the seasons. As the Earth revolves around the Sun, it also spins on its axis every 24 hours. If the Earth’s axis were not tilted the 23.5 degrees it is, the sun would shine directly on the equator at noon at all times of the year and there would be no seasonal changes of temperature and weather.
There would also be no winter or summer solstice or spring or fall equinox. We know that the summer solstice marks the longest day of the year, the winter solstice marks the shortest day of the year. In between are the vernal and autumnal equinoxes and we are approaching the vernal equinox this year on March 20th.
Our ancestors did not think about seasons in terms of the earth revolving around the sun, or axial tilt, but they were keen observers of the sun. They knew very well when the weather would warm up and days would get longer and when winter was approaching. For them, it was a matter of survival to be in touch with the changing seasons. These changes, they knew, were connected with the rising and setting points of the sun.
Almost every ancient culture we know had a sun priest or sun watcher. Perhaps the first astronomer, his job was to track the sun, and by observing its rising and setting points throughout the year, the changing of seasons could be foretold. One of the oldest markers of sunrise and sunset points is Stonehenge in England. Certain alignments of the giant standing stones marked the solstices and equinoxes. In the US, the ancient Anasazi Indians of the southwest were dedicated sun watchers. You too can try your hand at tracking the sun with a fun and educational exercise. You won’t need to erect large standing stones! You will only need a pencil and paper.
To see how much the sun’s rising or setting points change on a daily basis, try this. First decide whether you want to observe sunrise or sunset. Both will yield the same results, so you need only choose sunrise if you are normally an early riser. Next get paper and pencil and make a rough sketch of the horizon (obviously sketch west for sunset and east for sunrise.) The spot you sketch from will be your observing position, so choose a spot you can get to easily. You will want to sketch to the north and south of your east west points. These sketches don’t need to be a work of art, and you don’t need to locate exact east or west. A rough outline of trees and buildings will do fine. Picasso’s are not necessary!
Next, you want to watch for the sun to rise or set and mark the place on your horizon sketch. Dating the mark will serve as a reference. You may make the observations on a daily or weekly basis; twice a week will yield good results. The only thing you have to be sure to do is to make your observations from the very same place every day.
Unless you are normally an avid sun watcher, you will probably be surprised at your results. On March 20th, the sun will rise and set due east and west; after the equinox, the sun will continue its northward travel heading toward the summer solstice. Make your observations as long as you like. You will no doubt think about them in the future as you watch the seasons go by!
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