OBJECTIVES:

• Describing and comparing motions in our Solar System.
• Distinguishing between rotation and revolution.

VOCABULARY:

• axis
• orbit
• revolution
• rotation

MATERIALS:

• worksheet
• Solar System Placemats

Students learn about rotation and revolution.

BACKGROUND:

Students should now be aware of the great movements that occur in the Universe. Movement is also present throughout our Solar System. Even the Sun moves within the Milky Way Galaxy! You may want to ask them what evidence suggests to us that the Earth moves. The rising and setting of the Sun and Moon implies that one of the objects is moving. The changing positions of the stars, Sun, and Moon also implies movement of longer occurrence.

The key concepts to emphasize are that the Earth revolves around the Sun or orbits around a central point. The Earth also rotates on its axis or on itself. Although simple, these terms are easily confused. Use the worksheet to help student understand.

An example of revolve and rotation is a person who is sitting on a horse attached to a Ferris wheel. The person in the horse is revolving around the center, however rotation of the horse and person would occur if the person in the horse spins. The Earth, spinning on its axis, revolves around the Sun. The Moon, rotating on its axis, revolves around the Earth.

Rotation is a little more involved because students need to understand an axis. An axis is an imaginary line around which an object spins on itself. The Earth's axis is an imaginary line that runs through the north and south poles. You can use a basketball spinning on a finger as an example of rotation. Rotation causes day and night, and the tilt of the axis (23 ½ ^o) causes the seasons. The quality of the sunlight caused by the tilting of the axis is the major factor causing the seasons, not the distance from the Sun.

PROCEDURE:

1. Ask the students what evidence suggests to us that the Earth moves. Explain how the passing of day and night are cause by rotation.
    
2. You may want students to work in groups of 4 or 5 and have them illustrate to you the difference between revolution and rotation. Students should revolve around a central student, but they should also be rotating on their axis as they revolve.
    
3. The placemats are a way to get students to learn to observe and collect information. The orbit of each planet defines their revolution around the Sun. Point out the rings around Jupiter, Saturn, Uranus, and Neptune to the students. Tell them that the rings define the planet’s rotation. These objects circle the planet in a band . The planet’s axis is perpendicular to this band.

4. Draw a picture of the orbits using the diagram below as a model. Ask students to look closely at the orbits. Point out that the planets revolve in very defined areas, along the lines. Tell them the orbits are not wild! The only planet that has an eccentric (a little on the wild side) orbit is Pluto. Its orbit actually brings Pluto closer to the Sun than Neptune during some years.

5. Have the students use the Solar System placemat to help answer the questions on the worksheet.
    
   Answers: A = revolves; B = rotates; 1. An axis is an imaginary line through an object around which it spins. The point on the axis does not move. 2. The Earth revolves around the Sun. 3. The Earth rotates on its axis. 4. Yes. The axis points away from the Sun as it rotates. 5. The orbits of Mercury through Neptune are "flat" - they all lie in the same plane. The orbits of these planets are also almost circular. Pluto is the exception: its orbit is tilted about 20^o from the other planets, and it has an elliptical (oval) shape.

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