Slide 3 of 26
Notes:
Why is it warmer in summer than in winter?
The wrong answer is that we are nearer the sun during summer. The annual orbit of the earth around the sun is nearly circular, i.e. the distance from the center of the earth to the sun is approximately constant. In fact the orbit is slightly elliptical, with the earth closet to the sun in January during the northern hemisphere WINTER. Because of the tilt of the earth’s axis, we in Madison are during summer daytime slightly closer than the center of the earth, but because the sun is so far away the fractional change is distance is extremely small and has a negligible effect.
The right answer is that in summer the sun is higher above the horizon, so that the same amount of heat energy is distributed over a smaller area of the earth’s surface. The processes by which heat leaves the earth’s surface are unaffected by sun angle but increase with the surface temperature. Thus in spring time the surface then warms up until the heat loss per unit area balances the increased incoming heat from the sun.