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Trace and cut out a large circle on lined paper. Print
"North Pole" on the top of the circle and "South Pole" on the
bottom. Draw a heavy horizontal line through the middle of
the circle to represent the equator.

Place two sheets of lined paper on a flat surface, and mark
an "S" in the center between the two sheets to represent the
placement of the sun. The lines on the paper represent rays
of solar energy, some of which was converted into heat.

Place the cut-out earth on the left-hand lined sheet with the
North Pole at the top and the lines on the circle matching
those on the sheet.

Which part of the earth receives the most radiation from the
sun when it is this position?

Move the North Pole to the right, as if the earth were tilted
toward the sun (remember, the earth tilts 23 1/2 degrees).

Which part of the earth receives the most radiation from the
sun now? You will see that more rays strike the northern
regions than the southern. Arrow heads can be added to the
parallel lines to emphasize how the rays strike the earth.

Next, move the earth so that it travels around the sun to the
other side (place the earth on the right-hand sheet of lined
paper). Be sure the earth remains in the same tilted

Which areas on the earth receive more and which receive less
solar energy? You will see that, due to the tilt of the
earth, the polar regions alternate in receiving more or less
solar energy.

You will realize that the changing angles of the sun's rays
cause the changing seasons. In the northern hemisphere, the
sun is low in the sky in winter. In the summer, it is more
nearly directly overhead.

So what does this have to do with the Vernal Equinox?

Try this:

Shine a flashlight through a cardboard tube to keep the rays
from spreading outward. Aim the tube horizontally at the
equator of a globe, and describe the spot of light that is
projected. Move the light gradually toward the North Pole
while continuing to hold the tube in a horizontal position.

Decribe the spot of light that is now projected. (It is
larger because the rays strike the surface at more and more
of a slant as the light is moved toward the pole.)

Make an analogy to the radiant energy reaching the earth from
the sun.

Now attach several small thermometers to the globe. Place a
lamp 8 inches from the globe, so that the thermometer on the
equator is in the center of the lighted half of the globe.

After three minutes, compare the thermometer readings. You
will find that the temperature readings decrease as they
approach the poles.

And try this:

Fill two identical cardboard boxes or milk cartons with equal
amounts of soil or sand. Insert a thermometer at the same
depth in each box. Set both boxes in the sun, propping one
so that the sun's rays strike it directly. Record tempera-
ture readings every ten or fifteen minutes.

Results can be graphed. You will see that the temperature
rises more quickly and higher where the sun's rays strike the
soil directly.

Analogies can be made to various places on earth.

Fill one box with sand and another box with soil and prop
them so that they both lean toward the sun. After 15 minutes
in the sun, take temperature readings from both. Are they
the same, or not?

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