Chapter 10.2, Problem 4P

Many people mistakenly believe that the seasons are caused by the earth’s varying proximity to the sun. In fact, the distance from the earth to the sun varies only slightly during the year, and the seasons are caused by the tilt of the earth's axis. As the earth travels around the sun during the year, the tilt of the earth's axis causes the northern hemisphere to vary between being tilted toward the sun to being tilted away from the sun. Figure 10.50 shows the earth as seen at a certain time of year from a point in outer space located in the plane in which the earth rotates about the sun. The diagram shows that the earth's axis is tilted 23.5° from the perpendicular to the plane in which the earth rotates around the sun. Throughout this problem, assume that the sun rays are parallel to the plane of the page.

 
Figure 10.50 Earth and sun.

1. Locations A and B in Figure 10.50 are shown at noon. Is the sun higher in the sky at noon at location A or at location B? Explain how you can tell.
2. During the day, locations A and B will rotate around the axis through the North and South Poles. Compare the amount of sunlight that locations A and B will receive throughout the day. Which location will receive more sunlight during the day?
3. Based on your answers to parts (a) and (b), what season is it in the northern hemisphere. and what season is it in the southern hemisphere in Figure 10.50 Explain.
4. At another time of year, the earth and sun are positioned as shown in Figure 10.51 . At that time, what season is it in the northern and southern hemispheres? Why

Flgure 10.51 Earth and sun at another time of year.

At yet another time of year, the earth and sun are positioned as shown in Figure 10.52 . At that time, what season is it in the northern and southern hemispheres? Why? Give an either-or-answer. (Notice that Figure 10.51 still shows the tilt of the earth’s axis.)

Figure 10.52 Earth and sun at another time of year.