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Download Planets orbit the Sun at different distances.
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Transcript
KEY CONCEPT Planets orbit the Sun at different distances. STANDARDS 8–4.1 Summarize the characteristics and movements of objects in the solar system (including planets, moons, asteroids, comets, and meteors). BEFORE, you learned NOW, you will learn • Earth orbits the Sun • The Moon is Earth’s natural satellite • The Moon’s features tell us about its history • What types of objects are in the solar system • About sizes and distances in the solar system • How the solar system formed EXPLORE Planet Formation How do planets form? PROCEDURE 1 VOCABULARY astronomical unit (AU) p. 657 ellipse p. 657 Fill the bowl about halfway with water. 2 Stir the water quickly, using a circular motion, and then remove the spoon. MATERIALS • • • • bowl water spoon wax pieces 3 Sprinkle wax pieces onto the swirling water. WHAT DO YOU THINK? • In what direction did the wax move? • What else happened to the wax? Planets have different sizes and distances. MAIN IDEA AND DETAILS Put sizes and distances in the solar system into a chart. You may have seen some planets in the sky without realizing it. They are so far from Earth that they appear as tiny dots of light in the darkened sky. If you have seen something that looks like a very bright star in the western sky in the early evening, you have probably seen the planet Venus. Even if you live in a city, you may have seen Mars, Jupiter, or Saturn but thought that you were seeing a star. Mercury is much more difficult to see. You need a telescope to see the large but distant planets Uranus and Neptune. Like the Moon, planets can be seen because they reflect sunlight. Planets do not give off visible light of their own. Sunlight is also reflected by moons and other objects in space, such as those called comets and asteroids. However, these objects are usually too far away and not bright enough to see without a telescope. Why do planets look bright? Chapter 19: Our Solar System 655
