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Ch11 - Assignment Chapter 11 Class Astronomy I Date October...

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Assignment: Chapter 11 Class: Astronomy I Date: October 3 rd , 2007 Review Questions 1. Mercury and Venus are both inferior planets whose orbits around the Sun are smaller than the Earth’s. They appear after sunset over the western horizon and as a morning star before the Sun in the eastern sky. But they are impossible to see during midnight because it is between the Earth and the Sun. 2. Naked-eye observations of Mercury are best made at dusk or dawn, but the best telescopic views are obtained in the daytime when the planet is high in the sky, far above the degrading atmospheric effects near the horizon. 3. Mercury orbits so close to the Sun that it is exposed to sunlight that on average is about 7 times as intense as on the Earth. So even when Mercury is at nearest to the Earth, we can’t see the details of Mercury’s surface because of such strong sunlight. 4. Since Mars is a superior planet with an orbit larger than the Earth’s orbit, Mars is best seen at opposition when it is on the opposite side of the Sun from Earth. Some oppositions provide better views of Mars than others because Mars has a noticeable elongated orbit. Therefore, we get the best view of Mars when it is simultaneously at opposition and near the perihelion of its elliptical orbit. 5. During retrograde motion, Mars is best seen from Earth because it is closer to Earth than in forward motion, and it slows down in its orbit to less the Earth’s orbit pass it by. 6. The picture of Venus in Figure 11-4b shows a faint ring surrounding the planet. This is from the sunlight scattering by Venus’s atmosphere, producing that luminescent ring around the planet. Therefore, the photo must have been taken during daytime when the sunlight was strong. 7. Larry Niven assumed that Mercury exhibited synchronous rotation with the Earth. However, Rolf B. Dyce and Gordon H. Pettengill proved using Doppler Effect that as Mercury rotates, one side of the planet approaches the Earth, while the other side recedes from the Earth. 8. 3-to-2 spin-orbit coupling explains that the planet makes three complete rotations on its axis for every two complete orbits around the Sun. The Sun’s gravitational force on the near side of Mercury’s long-axis is greater than the force on the far side. This tends to twist the long axis to point toward the Sun. Therefore, from one perihelion to the next, alternate sides of Mercury face the Sun. The Doppler Effect experiment proved this rotation to be true. 9. Venus’s perpetual cloud cover makes it impossible to measure the planet’s rotation using visible-light telescopes. So in order to penetrate the planet’s perpetual cloud cover, astronomers used radio waves and the Doppler Effect to measure the rotation of Venus.
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