問題詳情
(二)You may have heard references made to the “dark side” of the moon. This popular termrefers to the fact that the same physical half of the moon, the “near side,” is always facing theearth, which in turn means that there is a far side or so-called “dark side” that is never facing theearth and can only be seen from space. This phenomenon has nothing to do with the periodic light and dark we see as the phasesof the moon change. Sometimes people refer to a new moon as a “dark moon” because themoon is fully in shadow as viewed from the earth, but that’s not the same thing as the dark sideof the moon. The side of the moon facing us during a new moon is the same as any other moonphase, such as a full moon when we can see the entire face So why can we only see one side of the moon from the earth? We all know that the earthrotates on its own axis, so theoretically, the moon should also do the same, allowing us to get afull picture of the planetoid. Why are we limited to seeing only half the picture? It turns out thatthe speed at which the moon rotates has led to this particular phenomenon. Millions of yearsago, the moon spun at a much faster pace than it does now. However, the gravitational influenceof the earth has gradually acted upon the moon to slow its rotation down, in the same way thatthe much smaller gravitational influence of the moon acts upon the earth to create tides. Thisinfluence slowed the rotational period of the moon to match that of its orbit – about 27.3 days –and it is now “locked in” to this period. Another interesting fact is that actually a little bit more than half of the moon’s surface isobservable from the earth. Since the moon’s orbit is elliptical, and not circular, the speed of itsorbital travel increases and decreases depending on how close it is to our planet. However, therotational speed of the moon is constant. This difference between orbital speed and rotationalspeed means that when the moon is farthest from the earth, its orbital speed slows down justenough to allow its rotational speed to overtake it, giving observers a small glimpse of theusually hidden area. The term for this “rocking motion" of the moon is called libration and itallows for 59 percent of the moon to be seen in total Finally, one reason that the far side of the moon is frequently referred to as the “darkside” is because many people mistakenly think that it never sees any light from the sun. In thatsense the term “dark side” is wrong and misleading. In fact, since the moon is constantlyrotating on its own axis, there is no area of the planetoid which is in permanent darkness, andthe far side of the moon is only completely devoid of sunlight during a full moon – when thesun is facing the moon with the earth in between.
【題組】73. What is mentioned in this passage?
(A) A space mission that unveiled the hidden side of the moon.
(B) The reason why the moon is indispensable to the earth.
(C) A misconception about the moon.
(D) A possible threat the moon is facing.
參考答案
答案：C
難度：非常困難0
統計：A(0),B(0),C(0),D(0),E(0)