Seasonal Science
Each year we experience the four seasons: spring, summer, fall, and winter, but what causes the changes in the season?
Everyone knows we measure a year as one complete orbit of the earth around the sun. Consequently many believe the changes
in the seasons are somehow related to this orbit. If this were true than how can it be that in the northern hemisphere we
are closer to the sun during the winter?
As the Earth travels in orbit around the sun, it also spins on an axis. The axis is an imaginary line which passes through the earth, exiting at the poles. One complete revolution on this axis takes approximately twenty four hours, hence the measurement of one day. The axis makes a 23.5 degree angle measured with the perpendicular to the celestial equator (a projection of the Earth’s equator into space). As the Earth orbits the sun, the axis always stays pointing in the same direction; because of this, part of the year the northern hemisphere will lean toward the sun, and the other part of the year the southern hemisphere will.
So now that we know about the tilt, how does this tilt bring about the changes in the seasons? When the northern hemisphere tilts away from the sun its rays hit this part of the Earth at a smaller angle. This causes the light created by the sun’s rays to be distributed over a larger surface; therefore these areas receive less heat than others. Consequently the southern hemisphere experiences summer while the northern hemisphere experiences winter. Note: On the equator the Earth’s tilt has a very limited effect and hence spring, summer, fall, and winter do not exist there however, weather patterns may cause a "wet season" and a "dry season".
This means the seasons are a result of the tilt of the Earth’s axis. If this tilt did not exist there would never be a change in how the rays from the sun hit the Earth’s different regions and the seasons would not exist. Now that we know the scientific reasons for the seasons we may find ourselves asking one last question. Without this scientific knowledge, how did our ancient ancestors know when the weather would warm up and when winter was approaching?
Our ancestors paid close attention to the sun. By tracking the sun’s rising and setting points throughout the year the changing of the seasons could be determined. On the Spring and Autumn Equinoxes the sun travels through the celestial equator and equal amount of day and night occur. The sun also rises due east and sets due west. As June 21st (the summer solstice) approaches, the days grow longer and the sun rises higher in our sky at noon. At the same time the sun is also rising and setting further north of east and west. During this time the northern hemisphere is pointing toward the sun. Alternatively, as December 21st (the winter solstice) approaches, the days grow shorter and the sun is lower in our sky at noon. The sun is rising and setting south of east and west. During this time the northern hemisphere is pointing away from the sun. These are observations that we today can make, and possibly feel closer to our ancestors.
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