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2. 1.The Parts of the Solar System 2

3. We live on the planet Earth Vocabulary Planet A large, solid object that travels around a star 3

4. Earth is one of nine planets circling a star we call the sun The sun and the nine planets make up our solar system 4

5. Vocabulary Solar system The sun and the nine planets 5

6. The most common theory of how the solar system was formed was by circulating gases and dust 6

7. 7 A chemical reaction occurred with heat to cause an explosion causing objects to form during cooling

8. 8 Video Birth of a Solar System

9. Each of the nine planets move in an orbit around the sun Vocabulary Orbit A curved path that each of the planets moves around the sun 9

10. The size of a planet’s orbit depends on the distance of the planet from the sun 10

11. Closer planets have smaller orbits. Planets far from the sun have large orbits 11 MercuryVenusEarthMars

12. All the planets are held in orbit by a force called gravity Vocabulary Gravity A force that acts like a pull between the sun and planets 12

13. Without gravity, the planets would drift into space 13 The space shuttles sent to space by NASA are held into orbit around the Earth by gravity

14. Some planets have smaller objects called moons 14 Vocabulary Moons A small object in orbit with a planet

15. There are more than 50 moons orbiting the planets of the solar system Each moon is held in orbit by the gravity between the moon and its planet 15

16. One moon orbits Earth 16

17. Asteroids and comets are smaller objects in the solar system 17

18. 18 Vocabulary Asteroids An object made of rock and metal that orbits the sun Asteroids orbit the sun in a belt between the planets Mars & Jupiter

19. 19 Vocabulary Comet An object made of ice, gas, and dust that orbits the sun A comet has a bright fiery head and a long tail of light

20. 20 Comets have very large orbits and travel to the edge of the solar system