THAT'S WHY THEY CALL IT SPACE

Category:modeling

Learning Objectives:
Student will be able to:
1. Calculate scale distances and sizes for modeling the solar system. Choose an appropriate and usable scale.
2. Set up a scale model using their calculated distances.
3. Relate actual distances to difficulties in discovering and exploring the planets.

Materials, equipment and/or facilities:
metric rulers
yellow poster board for suns
long metric tape measure or rolling measurer
card stock and tape
markers and fine point pens
modeling clay
1 or more binoculars (optional)
notebook paper
compass for drawing circles
wires, sticks, or blocks to support model planets
calculators

Sequence and duration of each part of lesson:
Most representations of the solar system use one scale for the size of planets and a different scale for the distance between them. By producing a model with just one scale, students can get a much more accurate idea of the true size of the solar system and the difficulties of space exploration.

Students design and set up an outdoor solar system model using just one scale. These models will tend to be very large. A kilometer in length is not unusual. The model is then viewed from different positions to see how hard it is to see other planets from the Earth, how small the sun looks from the outer planets, etc.

2 class periods total.

First Class Period: Students can work in teams that range from 3 or 4 students up to the whole class. For best results, each student should have a specific research and calculation assignment. Assign students to research the dimensions of our solar system. Provide several sources of this information so that values given differ. Encourage students to evaluate the sources and choose which value to use.

Review calculations of proportions and metric units as needed. Have students fill in actual diameters and distances on a chart like the following:

Object	Diameter (km)	Model Dia. (mm)	Ave. Dist. from sun (km)	Model Distance (m)
Sun			------------
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto

Have students choose a size in centimeters they think would be appropriate for the sun. Have them use this diameter to set up the proportion:
model diameter : actual diameter = model distance : actual distance.

Using the proportion, have them calculate the model distance from the sun to Pluto. Will this model distance fit within the area available? Have them adjust the model sun diameter and re- calculate or think of another way of adapting their model until they have a size that will fit. Models should not simply fold back and forth across the area or the sense of great distances will be lost. When their model sun diameter is set, they should complete the rest of the chart. Have each team draw and cut out a model sun of their chosen size from poster board. Next they should choose how to represent the planets (drawn on cards, holes in cards, clay balls, or other). Have them prepare their model planets.

Second Class Period: Teams measure off distances and set up models. If possible, mark off 10 meter intervals ahead of time to speed up model setup.

SPECIAL SAFETY CONSIDERATION Models will be large. The visible part of the sun is 1,390,000 kilometers across. If students use 13.9 centimeters for the sun (a logical a simple choice) the model distance to Pluto becomes 590 meters. Because the class is spread out so far it helps to arrange for assistance from a second adult. If models are set up near streets, emphasize traffic safety and supervise carefully.

Have the team stand by Earth and see how hard it is to see the outer planets. Try looking at them through binoculars to simulate using a telescope to study the planets from Earth. Have them stand by an outer planet and see how tiny the sun looks compared to the size it looks from Earth. Point out how much closer together the inner planets are than the outer ones.

Clean up models and return to the classroom.
Discuss the following questions:
1. Why were the planets beyond Saturn not known anciently? [too far away, fainter than many stars]
2. What would the sun look like from Pluto? [a bright star]
3. Why are we unlikely to send manned missions beyond Mars until far in the future? [so far the trip would take many years]
4. Proxima Centauri, the nearest known star, is about 40.68 million million kilometers away. Using your scale, what would the model distance be to Proxima Centauri? [With a 13.9 centimeter sun, it would be 4,068 kilometers, about from Utah to New York.]
5. The shuttle flies about 40,000 km per hour. How far across your model would it go in a month? [720 hours = actual distance of 28.8 million kilometers; on the above scale, just 2.88 meters.]
Invite students to come up with their own "Gee whiz!" comparisons.

Evaluation: based on team models and charts and individual participation in discussion. 

Related Resources: Once students have chosen a size for the sun in centimeters, multiply this number by 10,000 and then divide by the actual size of the sun in kilometers. Enter the answer on your calculator as a constant. This constant times the number of millions of kilometers from the sun to a planet will give the scale distance in meters. For example, if I choose 13.9 cm. for my model sun to represent 1,390,000 kilometers of diameter, the calculation would be:
13.9 x 10,000 ö 1,390,000 = 0.1
If my source says Mercury is 57.9 million kilometers from the sun, my model distance is 57.9 x 0.1 = 5.79 meters.
To find the size of a planet model in millimeters, multiply the planet size in kilometers by this same number, then divide by 1,000. If my source says Mercury is 4,900 kilometers in diameter, I multiply 4,900 x 0.1 = 490. 490 divided by 1,000 is 0.49 millimeters for the size of Mercury. So in this scale Mercury is about 1/2 millimeter. Jupiter would be 14.3 millimeters (just over 1/2 inch) on this scale. This gives you an idea of the size your model planets will be.