Instructions and Questions

Carry out the steps below in collaboration with your permanent group. Refer to the accompanying handout Figures 2-1 and 2-5 as needed.

1. In Figure 2-1, the angle of the sun above the horizon varies between figures (a), (b), and (c). The same "unit" of solar radiation (say, in calories per second) between pairs of parallel lines strikes the earth's surface in each case. In each case, how much solar radiation strikes each single "unit" of surface area (say, one square meter). This is called the intensity of solar radiation. How does the intensity vary with sun angle?

2. In Figure 2-5, how does the sun angle (the angle between the sun's rays and a horizontal surface) generally vary with latitude? What does this imply about the intensity of sunlight at high vs. low latitudes?

3. Choose one of the three globes on the tables in the room, each illuminated by a slide projector (which plays the role of the sun, though if we had things positioned "to scale", the projectors would have to be about two miles away!). Notice that globes (should be) positioned so that the axis of rotation of each globe points in the same direction, just as it does (pointing toward Polaris, the North Star) when the real earth obits the sun.

1. What time of year is it at your particular globe? How can you tell?

2. In Figure 2-5, which figure (a, b, or c) corresponds to your globe? What perspective (that is, from where in space) does the figure show your globe?

3. How does the length of daylight seem to vary with latitude? How can you tell?

4. Note the (approximate) length of daylight at San Francisco's latitude, and compare it with the other globes. (Do the same on Figure 2-5.)

5. Note the sun angle at San Francisco's latitude, and compare it with the other globes. Does it seem to vary with time of year? (Does Figure 2-5 show the same variation?)

4. How do variations in the length of daylight and in sun angle each contribute to the cause of the seasons? Why do they vary? At what latitudes does this variation seem to be the greatest? What are the seasons like there, compared to here?

5. Bonus Questions: In Figure 2-5, in each of the figures (a), (b), and (c), when does the sun rise (before 6 am, at 6 am, or after 6 am)? When does it set (before 6 pm, at 6 pm, or after 6 pm)? How can you tell? In each figure, in what direction (that is, where on the horizon) does the sun appear at sunrise and sunset? Does this vary with latitude in each figure? [Hint: east is always in a direction along a latitude circle; north is along a longitude circle toward the North Pole.]

(There are many more questions of this sort that these diagrams can help you answer—the topic is very rich.)