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:
- 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).
- 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.
- 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.
- 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.
- 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.
- 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."
