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# 3-D Model of Earth (page 2)

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Author: Janice VanCleave

### 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.

### Design Your Own Experiment

1. A satellite is a body that revolves about a celestial body. A natural satellite is a celestial body that revolves about a larger 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 1.2). 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 (any of the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto) because they were discovered in 1610 by Galileo (1564–1642). Make a model of Jupiter and the Galilean satellite 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).
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 km = 0.389 AU

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

Prepare a data table like Table 1.1, 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.

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 moon 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's and Will Tirion's, 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?
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