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Problem Set 6 Solution

# Problem Set 6 Solution - Astronomy 201 Problem Set 6...

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Astronomy 201 Problem Set 6 Assigned: 8 November 2004 Due: 29 November 2004 Remember: No late homework and homework counts 40% of the total grade. Each question / problem is of equal weight and equals 5 points. Chapter 13: Review and Discussion – 1, 3, 9, 15, 18 Problems: 1, 4, 7, 9, 13 REVIEW AND DISCUSSION 1. How was Uranus discovered? Uranus was discovered by the British amateur astronomer William Herschel in March 1781. Herschel was engaged in charting the faint stars when he came across an odd-looking object that he described as “a curious either nebulous star or perhaps a comet.” It appeared as a disk in the Herschel's telescope and moved relative to the stars, but too slowly to be a comet. Herschel had found the solar system’s seventh planet. 3. How did Uranus come to be spinning “on its side”? It may have been hit by a large, planet-sized object when young or forming but there is no direct evidence for this either. 9. Why are the icy moons of the outer planets so dark? The icy moons of the outer planets are mostly dark because they may be coated with a thin layer of organic matter formed from the reaction of the surface material with light and solar radiation. 15. How do the rings of Neptune differ from those of Uranus and Saturn? Neptune has four dark rings, two quite narrow and two quite broad and diffuse. One of the rings is apparently “clumped” in places for unknown reasons, producing the appearance of partial ring arcs from Earth. 18. In what respect is Pluto more like a moon than a jovian or terrestrial planet? Pluto’s size and density are more similar to the moon Triton than they are to any other object in the solar system. It is neither rocky like the terrestrial planets nor gaseous and liquid like the jovian planets. Pluto also has an icy surface like Triton. Problems

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1. Calculate the time between successive closest approaches of (a) Neptune and Uranus (b) Pluto and Neptune (approximately—just compute the synodic period neglecting Pluto’s orbital eccentricity). Compare your answers with Neptune’s sidereal orbital period. Use the formula for synodic period from Chapter 9. 1/S = 1/P U – 1/P N for the closest approach timing. The orbits are “circular” so this suffices. (a) For Neptune and Uranus: 1/ S = 1 / 84.01 - 1/164.8 S = 171.37 years. (b) For Pluto and Neptune: 1/ S = 1 / 164.8 - 1/248.6 S = 488.9 years. The first synodic period is just over one of Neptune's periods; Uranus's period is about half of that of Neptune. The second synodic period is almost exactly three times Neptune's period and almost twice Pluto's period, Because of these near coincidences there has been speculation that these planets have been trying to synchronize their orbits with each other. 4.
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Problem Set 6 Solution - Astronomy 201 Problem Set 6...

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