Why do the upper and lower latitudes of the Earth experience changing seasons?
One might answer the question this way. The earth is tilted on its axis. This causes sunlight to be distributed unevenly on the Earth’s surface. Because of this different parts of the Earth become warmer and cooler through a year’s time. Now of course this is quite true, but it hardly is a complete response to the question since the background understanding relevant to the explanation of the seasons is not covered. Notice, as well, that this answer would fail the test for completeness quite miserably: a person who lacked an understanding of astronomy would simply be confused by this response. Consider this alternative, and far more complete, answer to the question. The Earth as well as the other planets move within the solar system in two different ways. First, they revolve around the Sun in elliptical orbits. The period of a complete revolution around the Sun for any given planet is the period of one year for that planet. The second motion is the rotation of the planet around its axis
