Lesson 5-3

1. Lesson 5-3 What Holds the Moon and Planets in Place?

2. How Planets Move Through Space A. The sun is slightly away from the center of the solar system B. All planets orbit the sun 1. Orbit – the path that a body follows as it revolves around another body 2. Planets orbit in an elliptical pattern (shaped like a flattened circle) 3. Because of elliptical orbits, each planet is closer to the sun at certain times during the orbit than others

3. 4. Orbits are caused when there is a balance between inertia and gravity. a. The 1st law of motion (Inertia): An object will continue to move in a straight line until an outside force acts on it. b. Gravity: A force that pulls everything toward the center.

4. c. Gravity and Inertia cause the planets to “fall” constantly in a curved path around the sun d. distance from a planet to the sun or from the moon to Earth never changes

5. The Moon A. The moon rotates as it orbits the Earth 1. A full rotation occurs every 29 ½ days 2. Same side of the moon always faces Earth B. The moon is bright at night because it reflects the sun’s light

6. C. Phases of the moon – Because the moon revolves around the earth we see it differently every night 1. crescent – less than half 2. gibbous – more than half 3. waxing – getting bigger 4. waning – getting smaller

7. D. Eight Phases 1. New Moon 2. Waxing Crescent 3. First Qtr 4. Waxing Gibbous 5. Full Moon 6. Waning Gibbous 7. Last Qtr 8. Waning Crescent