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# Solar System Scale: Miniature Model

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Author: Janice VanCleave

Our solar system consists basically of the Sun, the eight planets (celestial bodies that orbit a sun), and their moons, asteroids, comets, and space debris. The boundary of the solar system is called the heliopause, which is the limit the solar winds reach. Solar winds are streams of charges escaping from the Sun's atmosphere and flowing into the solar system. From the heliopause, the solar system is about 18.6 billion miles (29.8 billion km) across. The Sun is the largest celestial body in the solar system, having a diameter of about 870,000 miles (1,392,000 km). Pluto is the smallest planet at about 1,434 miles (2,294 km) across. All of the millions of asteroids and comets are much smaller than Pluto.

In this project, you will make a 3-D model to represent the sizes of celestial bodies in the solar system. You will also learn how to represent the distances between planets and between planets and their moons.

### Materials

• drawing compass
• metric ruler
• sheet of colored poster board
• scissors
• index card
• pen

### Procedure

Rounding the number to the closest centimeter, the model Earth's diameter would be 4 cm.

1. The diameter of Earth is about 7,973 miles (12,757 km). Using the metric scale of 1 cm = 3,000 km, calculate the diameter of the model Earth as follows:
• Earth's actual diameter ÷ 3,000 km/cm = model Earth's diameter
•                  12,757 km ÷ 3,000 km/cm = 4.252 cm
2. Use the compass to draw two circles with diameters of 4 cm (radius 2 cm) on the poster board.
3. Cut out the circles, then cut along a straight line (radius) from the circumference to the center of each circle.
4. Fit the two circles together at a 90° angle to each other (see Figure 10.1)
5. Prepare a legend showing the scale of the model by folding the index card in half. Write the scale, "1 cm = 3,000 km," on one side of the card. Stand the card alongside the model.

### Results

You have made a scale model of Earth.

### Why?

A scale model is a replica made in proportion to the object it represents. A solar system is a group of celestial bodies that orbits a star called a sun. Planets are large celestial bodies that orbit a sun. Models of bodies in our solar system, such as Earth, are valuable because they allow an observer to compare the relative sizes and distances of large things more easily.

### Try New Approaches

How does the size of Earth compare with the other planets in the solar system? Make more scale models, using the diameters of the planets given in Appendix 3. Science Fair Hint: Attach threads to the models and suspend them from a 4-foot (1.2-m) or longer dowel. Support the ends of the dowel, then take a picture of the models. Use the photo and models in your science fair display.

1. A satellite is a celestial body or man-made body that revolves about another celestial body. Earth has one natural satellite, the Moon. Design a scale model that accurately represents the size of both Earth and the Moon and the average distance between them. The Moon's diameter is 2,173 miles (3,476 km). The average distance between the centers of Earth and the Moon is about 240,250 miles (384,400 km). Use the scale 1 cm = 3,000 km. Make one sphere to scale for Earth and another for the Moon. Label the models "Earth" and "Moon." Calculate the length of string needed to represent the distance between them. Measure and cut string of the necessary length. Tape one end of the string to the center of the model Moon and the other end to the center of the model Earth. Ask helpers to hold the models, stretching the string taut between the models, while you take a photo (see Figure 10.2). Display the photo along with a legend indicating the actual sizes and distances along with the scale you used.
2. The planet jupiter has many moons. Its four largest are collectively called the Galilean satellites because they were discovered in 1610 by Galileo (1564-1642). Make a model of jupiter and the Galilean called Ganymede. The diameter of this moon is 3,293 miles (5,268 km). It orbits 668,750 miles (1,070,000 km) from jupiter. jupiter's diameter is 89,875 miles (143,800 km).
3.

Rounding the answer to the nearest tenth, Mercury is 0.4 AU from the Sun.

Prepare a data table like Table 10.1, giving the average distances of the planets in miles (km) from the Sun (distances shown are from Appendix 3) and in AU units. Calculate the AU distance to the nearest tenth as in the preceding example.

Table 10.1 Planets' Average Distances from the Sun

#### Distance, AU

Mercury 36 (58) 0.4
Venus 68 (108)
Earth 93 (149) 1.0
Mars 143 (228)
Jupiter 486 (778)
Saturn 892 (1.427)
Uranus 1,794 (2,870)
Neptune 2,810 (4,497)

1. The average distance between Earth and the Sun is about 93 million miles (149 million km). This distance is called an astronomical unit (AU) and is used as a measure of distance in the solar system. The AU measurement for any planet can be calculated by dividing the planet's distance in miles (km) by 93 million miles (149 million km). For example, Mercury is about 36 million miles (58 million km) from the Sun, thus the AU distance between the Sun and Mercury is:
•        36,000,000 miles + 93,000,000 miles = 0.387 AU
• 58,000,000 km + 149,000,000 million km = 0.389 AU
2. Use the AU distances to draw a scale model of the solar system.

### Get the Facts

1. By definition, natural satellites (moons) are smaller than the planets they orbit. Even the smallest known planet in our solar system, Pluto, has a satellite called Charion. Pluto is smaller than Earth's moon, and Charion is even smaller. Find out more about the natural satellites of the planets. Do all the planets have satellites? How do their sizes compare with the size of the planets they orbit? Make models of the planets and their satellites. For information, see Patrick Moore and Will Tirion, Guide to Stars and Planets (Cambridge: Cambridge University Press, 1993).
2. The sixth planet from the sun, Saturn, is known for particles that orbit the planet, creating what looks like rings as observed from Earth. Make a model of Saturn. How many rings are there? What are they made of? How large are they? What causes them to change in visibility? For information, see Ann-Jeanette Campbell, New York Public Library Amazing Space (New York: Wiley, 1997), pp. 124–128.