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如果你曾连续几周观察过月亮，你有可能会意识到 [music] Narrator: If you looked at the moon over the course of a few weeks, you'd probably
它每天看起来都有一点不一样。它阴影的变化是建立在月球在其轨道上的 notice that it looks slightly different every day. The change in its shadow is based on
位置决定的。我们把这个循环称之为月相，其周期也差不多 where the moon is in its orbit. We call this cycle the phases of the moon, and it occurs
是一周一次。然而每年至少会有两次非同寻常的事情发生。 roughly once a month. At least twice a year, however, something quite different
月亮经过地球的影子，使它在短时间内看起来及其特殊。 happens. The moon passes through the shadow cast by the Earth, causing it to look extremely
在地球上看，月亮在回到正常状态前会显得更暗 unusual for a short period of time. From the earth, the moon will appear to
且会呈现出一种深红色。这被称作月食。 darken and turn a deep red before eventually returning to normal. This is called a lunar
如果从宇宙的角度来看月食，看起来会像是这个样子。 eclipse. If we were to look at what happens from space during an eclipse, it would go
首先，月球会穿过一个叫做半影的地方， something like this. First, the moon passes through what's called the penumbra,
半影部分的阳光只有部分被遮挡。这只会造成月球亮度略微减弱。 where the sun's light is only partially obscured. This results in only a slight darkening
然而当月球继续沿着轨迹运动， of the moon. As the moon continues along its path, however, it enters what's
它会进入本影，那里所有来自太阳的直射光会被遮挡。但若是所有光都被遮挡了， called the umbra, where all direct light from the sun is blocked. But if the sun is blocked,
为什么月球会泛红呢?当阳光从地球边缘经过时， why does the moon turn red? When light from the sun goes by the side of the Earth,
阳光会穿过一层厚且长的地球大气层。波长较短的光 it passes through a long and thick layer of Earth's atmosphere. Shorter wavelengths
例如蓝光，被大气层分离。所以当阳光到达月球的时候， of sunlight, like blue, are scattered by the atmosphere, so by the time the light has finished
更多类似于红光的长波被留了下来。 its trip to the moon, more of the longer wavelengths, like red, are left over.
在地球上，同样的事情也会在你所处的地区逐渐进入夜色的时候发生。 On the Earth, the same thing happens at sunset as the ground you stand on gradually passes
当月食结束，月球离开本影，便回到了原来的颜色。 into night. As the eclipse ends, the moon leaves the umbra, returns
然后离开半影，变得更加明亮且回到原来的轨道上。 to its normal color, and then leaves then penumbra, brightening and resuming its original
总而言之，整个过程之持续几分钟至几小时， cycle. Overall, the whole process lasts only from a few minutes to a few hours,
所以你若是想见到这一现象就得快一点。但是，只要你还醒着， so you'll have to be quick if you want to see it. But, as long as you're willing to stay awake,
你就能找到那个非同寻常的月球. you'll catch the moon as you won't see it too often.
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