phys0001_assignment01_ans

phys0001_assignment01_ans - In 19 years, there are 365.24 x...

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Solutions of Assignment 1 Due date: October 5, 2009 1) a) 1 A.U. = 1.5x10 11 m. b) The diameter of the Moon is about 3.5x10 6 m, and the mean Earth-Moon distance is about 3.9x10 8 m. c) The mean angular size of the Moon is tan -1 (3.5x10 6 / 3.9x10 8 ) = 0.51° d) The Sun has about the same angular size with the Moon. Hence, the diameter of the Sun is about (3.5x10 6 / 3.9x10 8 ) x 1.5x10 11 = 1.3x10 9 m 2) The sidereal day would be longer than a solar day. This is because if the directions of rotation and revolution were not the same, the advancing of the Earth in its orbit would take it to a position that it did not need to rotate a full turn to face the Sun again. This led to a shorter solar day. (Recall that in the actual Sun-Earth system, the Earth has to rotate a bit more than a full turn to face the Sun again.) 3) Looking up some websites or astronomical almanac, one will find that both Venus and Mercury are morning stars. 4)
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Unformatted text preview: In 19 years, there are 365.24 x 19 = 6939.56 days, and hence, there are 6939.56 / 29.53 = 235 months. In 19 years, there are 19 x 12 = 228 ordinary months. Finally, there are 235 - 228 = 7 leap months. 5) Recall that the ecliptic is defined as the apparent path of the Sun as the Earth revolves around the Sun. Hence, the ecliptic of Mars is the apparent path of the Sun as Mars revolves around the Sun. It has nothing to do with the rotation of Mars. Now, because the orbital planes of Mars and Earth coincide, the apparent paths are the same, i.e. the ecliptics are the same. The zodiacs are the same. However, because Mars' inclination angle is not the same as ours, its north celestial pole is not same as ours. Lastly, Earth is an inner planet as observed from Mars, and we do observe the retrograde motion of the inner planets. Hence, they can observe retrograde motion of the Earth....
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