5. Students find their ratio from dividing the distance they moved the paper from the index card by the size of the little sunlight spot. They then can use the ratio relation described above to find out the size of the Sun!



DISCUSSION:

Is the size of the Sun surprising when students consider the size of the Earth is 8,000 miles across? Is the Sun really anything similar to the Earth? Was the ratio relation easy to understand and use? Did students find the math difficult or powerful? How could students use the ratio relation to measure other things? What about the size of the Moon? Try holding a pencil out at arm's length towards the full moon. The pencil width should just wink out all of the moon's face. If you know the width of the pencil and the distance between it and your eyes, now you can find the ratio! Divide the distance to the moon (250,000 miles) by this ratio, and you have found the size of the moon!

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If you ask students what a particular season means to them, they'll probably mention the weather usually associated with it. Summer is hot. Winter is cold. Spring and Fall are in between. (For those of us living close enough to the poles, winter means snow, too!) A common misconception (even among a disturbingly large number of college graduates) is that the Earth is closer to the Sun during the summer, causing summer's warmer temperatures. This model, of course, is inconsistent with the fact that while the Northern Hemisphere has summer, the Southern Hemisphere has winter. Furthermore, while it is summer for the Northern Hemisphere, the Earth is actually slightly farther away from the Sun than during the Northern Hemisphere winter.

During the Northern Hemisphere's summer, the North Pole is tilted towards the Sun. During the winter, it is tilted away. This tilt causes the Sun to appear higher in the sky during the summer than during the winter. The higher Sun causes more hours of daylight and more intense, direct sunlight, or hotter conditions on the surface of the Earth. Questions to ask the class include: How is summer different from winter? What changes as winter gives way to spring? What changes are there as summer becomes fall? What about when winter approaches?

It is important to note that even without the tilt of the Earth, there would still be variations in temperature from one location to another, caused mainly by the curvature of the earth. Locations closer to the equator would still, on the average, be warmer than locations closer to the poles. Light and heat (radiation) from the Sun would still strike polar regions at more of an angle than nearer the Equator. This angle tends to "spread out" the same amount of energy over a larger area, thereby decreasing its intensity and the amount of heat it brings to the Earth. The activities addressing this topic demonstrate and test this assertion.

Students discuss results of these experiments. What caused the highest or hottest temperature? Was this related to the time of day? What were students able to discover from their measurements? How accurate were their predictions? What factors helped them to predict well? What conclusions can they make about the effect of the Sun's rays on the Earth? If done at intervals over a period of time, did earlier experiments help their predictions? What would happen if the experiment were done in a couple of months?

ACTIVITY: How Angle Spreads Sunlight

Be sure to remind students that looking at the Sun can cause permanent eye damage -- never look at the Sun directly!

The previous activity allowed students to observe the energy of the sunlight. However, since the angle of the sunlight influences the amount of energy it creates, it is important for students to observe this effect to understand why the winter on the Earth is colder than the summer is. This activity shows how light falling upon a tilted surface is less intense than if it were falling directly, demonstrating this "spreading out" of light by measuring how quickly and by how much the sunlight can warm two sheets of paper: one tilted, one not.

Materials: Two sheets of black construction paper; two pieces of cardboard or plywood; bricks or blocks to prop up board; masking tape; two thermometers.