Universe Cycle - Solar System (2)  Lab
 OBJECTIVES: Demonstrating how far the planets are from each other. Comparing the distance between planets. VOCABULARY: distance planet position MATERIALS: Meter tapes chalk Planet names Students compete to measure the distances of the planets from each Gas planets
BACKGROUND:

The planets revolve around the Sun, forming the Solar System. The orbits of all the planets are elliptical in shape, although on the scale of the Solar System they may seem circular. Measuring the distances from the Sun to the various planets was not an easy task. For early astronomers, this required making may difficult, often inaccurate observations through the Earth’s atmosphere. Today, using very sensitive ground- and space-based equipment we can measure these distances more precisely.

An accurate portrayal of the Solar System shows that the orbits of the planets are spaced further apart as distance from the Sun increases. For example, the orbits of Saturn and Neptune are further apart than the Earth and Venus. This observation was well known by the eighteenth century.

Bode’s Law gives a simple method for remembering the relative distances of the planets from the Sun. Bode’s Law is not a real physical law; it does not represent a real physical property of the Solar System. It just approximates the distances to the planets. This "law" gives the distance form the Sun to the planets when the numbers 0, 3, 6, 12, 24, etc., (doubling the previous number) are each added to 4, and the result is divided by 10. The results of this sequence are shown in the table on the next page. Note that Bode’s Law only works when the asteroid belt is included as a "planet" (current evidence suggests that no planet ever existed in the asteroid belt). One unit on the chart is equal to the distance from the Sun to the Earth. You will use these relative units in the Exercise below with the students.

 Planet Distance from the Sun,  via Bode’s Law Mercury 0.4 Venus 0.7 Earth 1.0 Mars 1.6 asteroid belt 2.8 Jupiter 5.2 Saturn 10.0 Uranus 19.6 Neptune 38.8 Pluto 77.2

In the lab, the students will measure these distances as meters e.g., "Venus" will be 0.7 meters, or 70 centimeters, from the Sun. Before the lab, we recommend that you use string to measure the correct distances. This can easily be laid out to see which student group has the correct answers.

PROCEDURE:
1. This lab is a game that demonstrates to the students how far the planets are from one another by making them think about placement of the planets (aka "students"). The object of the game is for the students to put themselves at the correct planetary order, but to also space themselves at the measurements that you give them. Eventually there should be a shape of a planet on a stick for each of the students (3 of each planet).

2. This lab works best outdoors. Divide the class into groups of eleven or more. Explain the lab to the students. Tell them that their groups will compete to see who can "measure" the relative distances of the planets from the Sun. Each student in the group will have a specific job. Nine of the students will be the planets. One student will measure, using the distances on the worksheet, and place the planets at the correct distances from the Sun. The remaining students should record the information and double check the measurements. Have the students meet before they go outside. They should decide which student will be each planet, and write the information on their worksheets. The designated students should then make a card with the name of their planet on it. This will make it clear to you which planet that person is representing.

3. Prevent cheating by having the groups start at 90 degrees from each other. Place an object to indicate the Sun in the center. You may want to make a round spot on the playground ground. This will make it easier to see which team is correct.

4. Go over how to measure with a tape measure. Emphasize that the students must cooperate, because they have to keep count of how far away they are from each other. Some students may realize that if they mark the ground off in meters using a piece of chalk and the tape measure they will complete the activity quickly. You may want to give them this technique as a hint if they get frustrated or confused.

5. After the groups finish the activity, check their results. The winner is the group that is finished first correctly. When all the groups have been measured, return to the classroom and have the students complete the remainder of the worksheet.

6. Some students may see that there seems to be some relationship between the distances. Do not try to explain Bode’s Law to the students, but acknowledge that they are observing a real relationship. If the students do not see a relationship, that is fine. The objective of the lab is just to experience the distances and to think about it. There are no right or wrong answers when you ask a student to "think."