UPSC Geography The Earth and the Solar System Question Bank The Solar System, The Earth and The Moon

  • question_answer
    An observer on the earth's surface always sees the same face of the moon because

    A) ?Its path of revolution around the earth is the same as that of the earth around the sun.

    B) ?Its period of rotation is the same as that of the earth.

    C) ?Its period of revolution around the earth is the same as its period of rotation around its own axis.

    D) ?Its direction of rotation is the same as that of the earth.

    Correct Answer: C

    Solution :

    ?The main reason that an observer on the earth's surface always sees the same face of the moon is that its period of revolution around the earth is the same as its period of rotation around its own axis. As a result of this phenomenon, only one part of the moon is visible to an observer on the earth's surface and the other part is always away from the view of the observer. Thus only 59 percent of the moon's surface is visible at the earth and the remaining 41 percent is never visible to us. As a matter of fact, a maximum of 50 percent of the moon's surface can be seen from the earth at a given time. The remaining 9 percent can be seen at different times depending upon the shift of the apparent edges of the illuminated part of the moon due to the relative motions and changes in the angle of view from the earth.


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