Blackout: What Causes a Solar Eclipse?
What causes a solar eclipse?
dime or any small coin
CAUTION: Never look at the sun directly, because it can permanently damage your eyes.
- Close one eye and look at a distant tree with your open eye.
- Hold the coin near and to the side of your open eye.
- Move the coin until it is in front of your open eye and about even with the end of your nose.
As the coin nears the front of your face, it comes between your eye and the tree. Less of the tree is seen, until finally all or most of the tree is no longer visible.
In this experiment, the tree represents the sun; the dime, the moon; and your eye, the earth. The coin is smaller than the tree, just as the moon is smaller than the sun, but they are both able to block out light and cast a shadow. The closer they are to the observer, the more light they block. The sun is so far away that it looks like a disk in the sky. The moon is close to the earth; thus, it can block out the sun's light when it passes directly between the sun and the earth. The blocking of the sun's light by the moon is called a solar eclipse.
Since the moon revolves (moves in a curved path around an object) around the earth about once a month, why don't eclipses happen each month? Solar eclipses occur when the moon passes directly between the sun and the earth. Repeat the experiment, changing the location of the coin. Hold the coin up so that it is slightly above your eye, then move it down so that it is slightly below your eye. Notice that the coin only blocks your view of the tree when the tree, coin, and your eye are in line with each other. A solar eclipse occurs only when the sun, moon, and earth are in line with each other.
- Determine why the whole earth is not darkened by a solar eclipse. Use a compass to draw a 20-inch (5O-cm)-diameter circle in the center of a poster board. Label the circle "Earth." Place the poster board on the ground in a sunny area outdoors. Stick a lemon-sized ball of clay on the eraser end of a pencil. The clay ball represents the moon. Push the point of the pencil through the center of the circle and into the ground so that the pencil stands upright. Observe the size of the shadow cast by the clay ball and the amount of the circle that it covers. If the shadow of the ball falls outside the circle, push the pencil farther into the ground. The shadow of the moon, like that of the clay ball, covers only a small portion of the earth.
- Does the shadow cast by the moon during a solar eclipse stay in one place on the earth? Repeat the previous experiment, making a mark on the poster board in the center of the clay ball's shadow. Mark the poster board every 30 minutes six or more times during the day. Use your results and the fact that the earth rotates (turns on its axis) to determine whether the shadow of the moon falls on different areas during a solar eclipse. Use diagrams to create a display to represent the results.
- During a total solar eclipse, the moon blocks the glaring light from the sun's photosphere (the visible surface of the sun), allowing the less intense layer of glowing gas around the sun, called the corona, to be studied. Demonstrate this by asking an adult to make a pinhole in the center of an index card with the point of a compass. Close one eye and hold the card over your open eye. Look through the pinhole in the card at the glowing bulb in a lamp. The print on the outside of the bulb can be read when looking through the pinhole. CAUTION' Do not look at the sun through the pinhole.
- Determine why some areas of the moon's shadow are darker than others during a solar eclipse by laying a sheet of typing paper on a table. Position a desk lamp about 14 inches (35 cm) from the paper. Place your hand between the light and the paper about 1 inch (2.5 cm) above the paper. Notice that the shadow of your hand is darker in the center than on the outside. Draw and display a diagram of a solar eclipse. Label the two parts of the shadow: the umbra (the darker inner part of a shadow) and the penumbra (the lighter outer part of a shadow).
Check it Out!
An eclipse of the moon is called a lunar eclipse. What is the position of the sun, moon, and earth during a lunar eclipse? Find out more about solar and lunar eclipses. What is an annular eclipse? Which type of eclipse occurs more often?
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