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# Chapter 2 - Chapter 2 Review Question Answers 1 Who wrote...

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Chapter 2 Review Question Answers 1. Who wrote down the equation for the law of gravita-tion? Newton proposed and developed the law of gravitation. 2. Which of the following most accurately describes the shape of Earths orbit around the Sun? (b) The Earth orbits the Sun in an elliptical orbit. 3. Of the following planets, which takes the longest time to orbit the Sun? (b) Uranus takes the longest because it is the farthest from the Sun. 4. What is a Sun- centered model of the solar system called? A Sun-centered model is a heliocentric model. 5. How long does it take Earth to complete a sidereal orbit of the Sun? A sidereal period is measured with respect to the distant stars. The sidereal period of the Earth is 365.26 days. 6. How did Copernicus explain the retrograde motions of the planets? By placing the Sun at the center of the solar system, the retrograde motion of the superior planets can be explained by visualizing the Earth on an inside track overtaking and passing the superior planet on the outer track. 7. Which planets can never be seen at opposition? Inferior planets, Mercury and Venus, can never go through opposition, which is when planets are on the opposite side of the Earth from the Sun. Which planets never pass through inferior conjunction? Superior planets can never be seen at inferior conjunction, which is when the planet is between the Earth and the Sun. 8 At what configuration ( superior conjunction, greatest eastern elongation, etc.) would it be best to observe Mercury or Venus with an Earth- based telescope? At what configuration would it be best to observe Mars, Jupiter, or Saturn? Explain your answers. In either case, the best time to observe a planet is when it appears farthest in angle from the Sun. Mercury or Venus can therefore be seen best at greatest eastern or western elongation. Mars, Jupiter, and Saturn are best seen at opposition. 9. What are the synodic and sidereal periods of a planet? The sidereal periods are the true orbital periods. They are measured with reference to the position of a planet or other body compared to the background stars. The synodic periods express the time taken to cycle through the configurations, such as superior conjunction to superior conjunction. 10. What are Keplers three laws? Why are they important? Kepler deduced three laws of planetary motion from Tycho Brahe’s observational data. The first law states that the planets orbit around the Sun in elliptical paths with the Sun at one focus. His second law says that a line joining a planet and the Sun sweeps equal areas in equal times. The consequence of this second law is that planets move faster the closer they are to the Sun, while slowing down the further they are away from it. The third law states that the square of a planet’s sidereal period around the Sun is directly proportional to the cube of the length of its orbit’s semimajor axis. This law implies that for any pair of planets, the one that has the greater average distance from the Sun has the longer year. The

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Chapter 2 - Chapter 2 Review Question Answers 1 Who wrote...

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