Demonstration: The Plane of the Ecliptic

©1995 The Regents of the University of California

by Beth Napier

Structure:

As explained in the Introduction section of this lesson, the path in the sky defined by the apparent motion of the Sun against the background stars (which is actually the plane of the Earth's revolution about the Sun) is called the Plane of the Ecliptic. This demonstration should help to explain to your students the concept of the Plane of the Ecliptic:

Bring in an aluminum pie pan or other flat, round container with a rim. Also bring some clay or play dough and a few marbles.

1. Place the lump of clay in the center of the pan.
2. Roll some thin strips of clay and make circular clay rings around the central lump.
3. Identify the central lump as representative of the Sun.
4. Identify the tracks formed by the clay rings as the orbital paths of the planets as they revolve around the sun.
5. Gently swirl the pan so that the marbles roll around the central lump in the tracks you have created.

The students should get the idea that if one were to look at the solar system from its outer edges, we would see that the planets revolve on a particular plane (the pan) and along a particular path (along the almost circular tracks).

Worksheets:

Have students name the planets and indicate the Asteroid Belt on Figure 1: "The Plane of the Ecliptic."

Have each student answer the following questions:

1. Which planet is not included in the diagram? [PLUTO]
2. Why was this planet left off the diagram? [BECAUSE PLUTO'S ORBIT IS QUITE INCLINED WITH RESPECT TO THE PLANE OF THE ECLIPTIC.] (Draw as much of this planet's orbit as you can fit onto the diagram).

Assignments:

Have your students describe, in writing, how this demonstration depicts the Plane of the Ecliptic. Encourage the students to experiment with the demonstration as they work on their compositions.