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# Seasons: Four Times of the Year (page 2)

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Author: Janice VanCleave

### Try New Approaches

How does the angle at which radiation strikes a surface affect the intensity of the radiation? Repeat the experiment three times, first holding the flashlight perpendicular to the paper. Then, without moving the end of the ruler touching the paper, tilt the flashlight about 45° from the paper. Finally, tilt the flashlight about 10° from the paper. Use a different color pen to trace the outline of each lighted area on the paper. Note that the amount of radiation leaving the flashlight is the same regardless of the angle of the flashlight. So the size of the lighted areas indicates how concentrated or intense the radiation from the flashlight is. Science Fair Hint: Display the overlapping circles, labeling each with its estimated area and the angle of light that produced it.

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1. Design an experiment to measure the change in the intensity of solar radiation during the day. One way is to secure graph paper to a board so that it will lie flat. Place the board outdoors on a level surface in a sunny area. Bend a large paper clip to make a stand for a 2-inch (5-cm)–diameter Styrofoam ball. Stand the ball on the graph paper. Using the technique in ''Try New Approaches," determine the area of the ball's shadow at different times during the day. Note: As the area of the light increases, its intensity decreases.
2. To determine the changes in intensity of solar radiation from season to season, repeat the previous experiment at noon on the first day of each week for as many weeks as possible.
2. Design an experiment to relate light intensity to the angle of the Sun's rays. One way is to record the angle of the Sun's rays each time the light intensity is measured. Determine these angles by hammering a large nail, such as a 16d nail into a block of wood until it stands straight and strong. Set the block outdoors, using a carpenter's level to ensure that the block is level. Tape a string to the top of the nail. Ask a helper to stretch the string from the nail to the end of its shadow. Use a protractor to measure the angle between the nail and the string, as shown in Figure 9.3. This is the angle of the shadow. Determine the angle of the Sun's rays using this formula:
angle of Sun's rays = 90° – angle of shadow

For example, in Figure 9.3 the angle of the shadow is 50°, so the angle of the Sun's rays is:

### Get the Facts

Solstice is combined from two Latin words, sol (Sun) and stare (to stand). Solstices are the times when the Sun, in its apparent annual motion, is at its greatest angular distance north or south of the celestial equator, which is an imaginary line in the sky projected from Earth's equator. On the days of the solstice, in summer and winter, the periods of daylight or 'darkness are the longest of the year. How does the position of the Sun affect the angle of the Sun's rays? Where is the Sun at the equinoxes? How do these positions affect the angle of its rays? For information, see Richard Moeschl, Exploring the Sky (Chicago: Chicago Review Press, 1993), pp. 12–15.

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