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# 3-D Model of Earth

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Author: Janice VanCleave

### Miniature Model

Our solar system consists basically of the Sun, the nine planets and their moons, 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—gaseous layer surrounding it—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.

### Getting Started

Purpose: To build a 3-D scale model of Earth.

### Materials

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

### Procedure

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

3. Use the compass to draw two circles with diameters of 4 cm (radius 2 cm) on the poster board.
4. Cut out the circles, then cut along a straight line (radius) from the circumference to the center of each circle.
5. Fit the two circles together at a 90° angle to each other (see Figure 1.1).
6. 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?

Celestial bodies are groups of natural objects in the sky, such as suns, stars, planets, and moons. A solar system is a group of celestial bodies that revolves around the sun. This means they move in a curved path around another object, which is also called orbiting. A sun is a star (glowing sphere of gas) that is the celestial body at the center of a solar system. If capitalized, Sun is the central body in our own solar system. Basically our solar system is made up of nine planets (celestial bodies that orbit a sun and shine only by reflected light), moons (small bodies in orbit around a planet) and other space debris (scattered pieces of something that has been broken). If capitalized, Moon refers to Earth's moon.

In this experiment you made a scale model (replica made in proportion to the object it represents) of the Earth, one of the planets of our solar system. A scale is a ratio between the measurements of a model and the actual measurements of an object. In a scale ratio the model measurement comes first. If the first value of the ratio is smaller, the scale drawing or model is reduced, such as the 1 cm/3,000 km in this experiment. Scale 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.

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