Winter

"No matter what you learn today, nine of you will go back to saying winter is caused by the earth being farther away from the sun," my high school science teacher told us. We were a class of ten.

While the elliptical orbit of the earth around the sun does cause it to be farther in some time periods, it does not fully account for those winter months.

The axis of the earth, the point around which it rotates, is tilted relative to the sun at about 23 degrees. A line drawn through the axis would point to the same position in space even as the earth moves around the sun.

So, as the earth revolves, different hemispheres are leaning either toward or away from the sun.

As a result, the sun's rays strike the earth at different angles. In summer, the angle is more direct, a sort of concentration of heat radiation. In winter, the angle is more obtuse, spreading the summer concentration over a larger area.

Suppose each yellow line represents 20 degrees Fahrenheit of the sun's heat energy. In summer, the small area receives 4 lines, about 80 degrees. In winter, a larger area receives the same energy that would have amounted to 80 degrees in the summer, but, being spread out, each locale is about 20 degrees. But remember, this is a very simplified explanation.