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  3. As countless photos from space can prove, the Earth is round the "Blue Marble," as astronauts have affectionately dubbed it. App

As countless photos from space can prove, the Earth is round the "Blue Marble," as astronauts have affectionately dubbed it. App

admin2009-04-23  4
问题     As countless photos from space can prove, the Earth is round the "Blue Marble," as astronauts have affectionately dubbed it. Appearances, however, can be deceiving. Planet Earth is not, in fact, perfectly round. This is not to say the Earth is flat. Well before Columbus sailed the ocean, Aristotle and other ancient Greek scholars proposed that Earth was round. This was based on a number of observations, such as the fact that departing ships seemed to be smaller as they sailed away, as one might expect if sailing across a ball says scientist Bill Carstensen of Virginia Tech in Blacksburg.
     Isaac Newton first proposed that Earth was not perfectly round. Instead, he suggested it was an oblate spheroid(扁球体) a sphere that is squashed at its poles and swollen at the equator. He was correct and, because of this bulge, the distance from Earth’s center to sea level is roughly 21 kilometers greater at the equator than at the poles.
    Our globe, however, is not even a perfect oblate spheroid, because mass is not distributed evenly within the planet. The greater a concentration of mass is, the stronger its gravitational(重力的) pull, "creating bumps around the globe," says scientist Joe Meert at the University of Florida. Also Earth’s shape changes over time due to a number of other dynamic factors. Mass shifts around inside the planet. Mountains and valleys emerge and disappear due to plate construction. Occasionally falling stars make the surface cave in. And the gravitational pull of the moon and sun not only cause ocean tides but earth titles as well. In addition, the changing weight of the oceans and atmosphere can cause the crust to be out of shape.
    Moreover, to even out Earth’s distribution of mass and stabilize its spin, "the entire surface of the Earth will rotate and try to redistribute mass along the equator, a process called true polar wander", Meert says.
    To keep track of Earth’s shape, scientists now position thousands of Global Positioning System receivers on the ground that can detect changes in their rising of a few millimeters, Meert says. Another method, dubbed satellite laser ranging, fires visible-wavelength lasers from a few dozen ground stations at satellites. Any changes detected in their orbits correspond to gravitational pulls and thus mass distributions inside the planet. It may not take much technology to understand that Earth is not perfectly round, but it takes quite a bit of effort and technology related above to determine its true shape.
选项 A、A number of photos from space show us that the earth is not round.
B、People think the earth is fiat, since its appearance deceived people.
C、Aristotle denied that the earth is flat, basing on the fact that Columbus sailed the ocean.
D、Tile fact that ships appeared smaller when they sailed away showed the earth is round.
答案D
解析 根据第一段的第四、五句可知亚里士多德和其它古埃及的学者认为地球是圆的。这样的认识是基于许多观察，例如驶离的船只看起来会越来越小，就像行驶在一个球体上所发生的情况一样。也就是说行走的船看起来变小了可以显示地球是圆的。本段前三句指出从太空拍摄的无数照片都证明地球是圆的，但是表面现象是欺骗人的，地球并不是绝对的球体。故可排除A；本段第二句说的表面现象是欺骗人的是指从太空拍摄的照片而言，不是指普通人们观察地面是平的，故排除B；亚里士多德否认地球是平的是基于许多观察而非哥伦布的航海，故可排除C。
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