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Darken a room, turn on a slide projector, and slowly rotate a globe of the earth counterclockwise in the light beam. The turning of the earth is called rotation. One complete rotation takes twenty-four hours (one complete day).

Now imagine how the eastern portion of the United States
experiences sunrise as the earth turns into the light and how the western portion eventually disappears into the shadow at sunset.

Try reversing the direction of rotation and comparing the
images. If Mother Nature allowed the rotation of the earth
to run in reverse (clockwise), would we go back in time? If so, would we all grow younger? Now, that's quite an image!

Back to reality! Place a piece of metal windowscreen into a 2 inch by 2 inch slide frame and project it onto a globe of the earth. The projector represents the sun and the globe presents the earth in its summer position.

You will see that the squares of the grid elongate toward the top and bottom of the globe.

Using this model, you should be able to realize that the
sun's radiation spreads out more toward the poles because of the greater angle at which it strikes the globe, and thus infer that light and heat are less intense toward the poles.

Now place a square piece of paper the size of one square of
the projected grid over the city where your school is
located. With a grease pencil, trace the square. Next,
revolve the globe so that it moves to its winter position.

The earth's tilted axis continually points 23 1/2 degrees in one direction throughout its revolution. One revolution
takes about 365 rotations (days). Are there any differences between the shape of the square and the square of light now cast on the same spot? You will note that the light is more spread out and can infer from that, that vertical radiation produces more warmth and light than slanted radiation.)

Other times of the year can be compared, as can other
locations on the globe (e.g., the Equator, Tropic of Cancer, Tropic of Capricorn).


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