The motion of the sun along the ecliptic is, of course, merely a reflection of the revolution of the earth around the sun, but the ancients believed the earth was fixed and the sun had an independent motion of its own, eastward among the stars. The glare of sunlight hides the stars in daytime, but the ancients were aware that the stars were up there even at night, and the slow eastward motion of the sun around the sky, at the rate of about thirty degrees each month, caused different stars to be visible at night at different times of the year.
The moon, revolving around the earth each month, also has an independent motion in the sky. The moon, however, changes its position relatively rapidly. Although it appears to rise and set each day, as does nearly everything else in the sky, we can see the moon changing position during as short an interval as an hour or so. The moon's path around the earth lies nearly in the same plane as the earth's path around the sun, so the moon is never seen very far from the ecliptic in the sky. There are five other objects visible to the naked eye that also appear to move in respect to the fixed background of stars on the celestial sphere. These are the planets Mercury, Venus, Mars, Jupiter, and the Saturn. All of them revolve around the sun in nearly the same plane as the earth does, so they, like the moon, always appear near the ecliptic. Because we see the planets from the moving earth, however, they behave in a complicated way, with their apparent motions on the celestial sphere reflecting both their own independent motions around the sun and our motion as well.
The ancient people believed that______.
A.the earth was spinning on the axis of the sky
B.the sky was a hollow sphere spinning around the earth
C.the patterns of stars on the sky would never change
D.the stars around the sky were not stationary
第5题
A.0.2MPa,2.5MPa*L
B.0.1MPa,2.0MPa*L
C.0.1MPa,2.5MPa*L
第6题
A.0.2MPa,2.5MPa*L
B.0.1MPa,2.0MPa*L
C.0.1MPa,2.5MPa*L
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