Astronomy > Solar > EARTH - MOON - PLANETS - STARS

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Grade Category: Middle School

Subject Category: Astronomy

Sub Category: Solar


Draw a 20 inch diameter circle on a chart or chalkboard. The circle represents the earth. Imagine that you are above the North Pole looking down upon the earth. Draw longitude lines across the diameter of the earth, intersecting the lines at the center of the circle (North Pole), and number them.

Now draw a 5 inch diameter circle 4 feet away from the "earth" to represent the moon. The earth and moon attract each other. The moon's attraction causes the ocean to bulge directly outward toward the moon, and there is another bulge on the opposite side of the earth. Draw the bulges, and letter the high and low positions of the ocean.

Describe the various tides from the longitudinal positions you drew, as the earth turns.

For example, you might say that from position 1, the tide seems to be coming in or rising (because the earth is moving into the bulge) and that from position 4, the tide seems to be going out.

You should be able to tell that there are 12 hours between one high tide and the next high tide and 6 hours between changes in tides.

Obtain a globe of the earth, and a ping-pong ball to represent the moon. Demonstrate that as the earth rotates on its axis, the moon goes around the earth in the same direction but much more slowly.

As you turn the globe and move the ball, gesture with your hand to show how the water on the globe is pulled toward the moon. (Although it is pulled almost directly in line with the moon, the tides lag just a bit.)

Try to carry a shallow pan of water across the room without spilling any water. (This will be very difficult to do.)

The sloshing motion is similar to the motion set up in great ocean basins around the world (e.g., the Bay of Fundy).

Use models of the sun, moon, and earth to show that:

  1. When the sun and moon are in line, their gravitational influences combine to produce the highest possible tides (spring tides);
  2. When they are at right angles to each other, their influences divide and produce lower tides (neap tides).

Use styrofoam balls of different sizes, and a bright light source, to explain the differences between stars and planets. (Stars produce their own light; planets reflect light.) You have books that tell the proportional differences among planets and the sun. Arrange your styrofoam balls in a pattern that shows their relative sizes and distances from each other. You could even label them.

If your books tell you which directions (orbits) the planets go, you can see how the planets revolve around one star, our sun. Is our sun a star? How do we know that?

Smaller objects, called moons, also reflect light, but they revolve around some planets. The Earth has one moon; Mars has two; Jupiter has thirteen; Saturn has ten; Uranus has five; and Neptune has two. (Pronounce: "YOOR-ann-us".)

The planets and moons orbiting around the sun make up the Solar System, which is but one tiny part of the universe.

How many planets are there?

How many stars are there? Probably, bazillions. Any person who is smart enough to be able to count that high is too smart to waste his or her time doing that. Bazillions is as good a word as any.

Is the universe the same thing as the galaxy?

Since I'm so nice (and brilliant), I will explain the difference: Galaxy is any of numerous large-scale aggregates of stars, gas, and dust, having one of a group of more or less definite overall structures, containing an average of 100 billion solar masses, and ranging in diameter from 1,500 to 300,000 light-years. The Milky Way is a galaxy.

Universe refers to all existing things, including the earth, the heavens, the galaxies, and all therein regarded as a whole. (Both definitions are from the American Heritage Dictionary.)

You might be interested in researching information on other objects in the Solar System such as asteroids, comets, and meteors.