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大家好，欢迎大家收看今天关于月食的第三部分视频 Hey guys and welcome to another video. Today is part three of our lunar
接下来，我们开始观察月食 series. We're going to be looking at the lunar eclipse. The lunar eclipse and the
我们经常很难分清日食和月食 solar eclipses are quite often confused with one another, however if you watch my
然而，如果你看过我之前介绍日食的视频， 你就会发现这两者有很大不同 other video on solar eclipses you will see that the two events are quite
首先，我们来了解一下月食是怎样发生的 different. First of all let's look at why the lunar eclipse happens. As the moon
就像我们之前看到的视频一样， 当月球围绕地球运行时，它会经历数个阶段 orbits the earth, as we have seen in the previous video, it goes through various
其中一个便是满月，回看第一个视频的示意图 phases. One of these is the full moon. Going back to the diagram from the first
我们可以看到月球围绕地球运行时会有轨道倾角 video we can see that the lunar orbital inclination means that as the moon
当发生满月的时候它仍然接受来自太阳的光 orbits around the Earth, when it is at full moon it is still receiving light from
因为月球的运行轨道要略低于黄道平面 the Sun because it orbits slightly under the ecliptic plane. About two to three
一年大约有两到三次月球的运行轨道会穿过黄道平面 times a year the moon's orbit crosses the ecliptic plane. As with the solar
此时，就像经历日食一样我们正经历着月食 eclipse this is when we experience a lunar eclipse. However, this time instead
然而，在这个阶段月球不是在地球和太阳之间运行 of the moon moving between the earth and the Sun it is the earth which moves
而是地球在太阳和月球之间运行,这意味着月食只能发生在满月期间 between the Sun and the moon. This means that a lunar eclipse can only occur
就像日食会在地球上形成阴影 during the full moon. As with the solar eclipse the earth forms a shadow. There
这个阴影有两部分，分别是本影和半影 are two parts to this shadow, the Umbra and the Penumbra. There are three types
月食有三种类型。第一种是月偏食 of lunar eclipses. The first is the penumbral eclipse. These are very faint
它很模糊，并且很难看到，一般不被称为月食 and hard to see and quite often aren't included in the list of lunar eclipses
因为它没有发出相似的红光 as they don't cause the familiar red glow. As you can see the photo of the
大家看图片上的月球在发生月食时光会慢慢变暗 moon during the Eclipse look slightly dimmer but unless you knew what you were
但是除非你知道自己能发现什么 looking for you can see why these eclipses are not quite a sought after as
你才可以看到为什么月食会这样变化，为了让这个变化更鲜明 their more dramatic counterparts. To highlight this here is an animation of
我们制作了一个动画来解释月偏食是怎样开始的和月食是怎样形成的 the start of a penumbral eclipse and even knowing that the Eclipse is
但还是有些难以注意到这两者的区别 occurring it's still quite difficult to notice the difference.
接下来的月食会看的稍微容易些 The next Eclipse is slightly easier to see,
这是月食的一部分，这时月球的一部分会进入到本影的阴影中 this is the partial lunar eclipse. This is when the moon is partially crossing
并且我们看到一部分红光会穿过月球的表面 into the umbral shadow and we see the red glow partially cross over the moon's
在月食的开始和结尾你仅能看到月球第一次进入到半影中 surface. At the very start and end of the Eclipse you can just see the moon first
在我们看到这种相同的红光的时候，月球有会有轻微的暗淡 enter the penumbral shadow. The moon has a slightly shaded appearance before we
现在到了最重要的时刻，满月。 see the familiar red glow. Now on to the main event, the full lunar eclipse. This
这时月球完全被本影遮住了 is when the moon is fully immersed in the umbral shadow. When this happens all
当这种景象发生时来自太阳的光被完全遮蔽 of the light from the Sun is blocked. The reason that the moon is still visible to
我们用肉眼也可以看到的原因是由于地球的大气层 the naked eye is due to the Earth's atmosphere. If we were able to stand on
如果我们可以站在月球上，我们会看到地球周围会有光圈存在 the moon at this point the earth would appear to have a glow around it, similar
和我们见到的日全食很相似 to how we see the moon during a full solar eclipse. Rather than the corona of
但不是像我们看到的日食的日冕层 the Sun being visible as with the solar eclipse, this glow is from the Earth's
这些光来自地球的大气层，当来自太阳的射线穿过太空到达地球时 atmosphere. As the rays from the Sun pass through space they are stopped by the
这些光被阻挡，从而造成了本影 earth producing the umbral shadow, however these rays can still pass
然而，这些光可以穿越大气层。 如果地球没有大气层，那么月食发生时就仅仅是一片黑暗 through the atmosphere. If the earth had no atmosphere the lunar eclipse would
没有一点点红色 just be dark, there wouldn't be a red tinge. But our
但是，在地表之上约有80公里的大气层阻挡了高强度的光 atmosphere extends about 80 kilometers above the Earth's surface leaving this
这便是月全食时月亮的形状 distinctive glow. This is what the moon looks like during a full lunar eclipse.
接下来一个重要的问题是为什么它是红色的？ So the next major question is why is it red? So as we explored earlier the sun's
我们之前说太阳的射线会穿越地球的大气层 rays pass through the Earth's atmosphere. If you've studied physics before you may
如果你之前学习过物理， 你对这个光照射到棱镜上会折射的动画会比较熟悉 be familiar with this diagram of light being refracted through a prism. This
这种现象的出现是由于不同波长的光在不同的角度折射会有不同 happens because the different wavelengths of light are refracted at
观看我的关于光波的视频可以了解到更多 different angles, see my video on light waves to learn more. A similar thing
同样的事情在地球大气层也会发生，由于大气有不同的组成成分 happens in the Earth's atmosphere. Due to the composition of our atmosphere the
从绿色到紫色端的光会被过滤过去 light from the green to violet ends of the spectrum are filtered out. This leaves
最后光谱只剩下大部分红色光没有被改变 the red end of the spectrum fairly untouched and allows this wavelength of
并且允许这个波长的光穿过大气层 light to pass through the atmosphere. This then reflects off
然后它照射到月球再反射到地球上，这时也被称为血月 the moon and back to earth giving us this red glow, also known as the Blood
好了，我们回到原话题，这便是我们在地球上体验到的不同过程的月食 Moon. So there we go. That is the different types of lunar eclipses we
我将会在文章里放一个链接 experience on the earth. I'll put a link in the description so you can look to
这样你就可以知道在你的家，你何时可以观看到下一次月食 see where the next lunar eclipse is where you are.
非常感谢您的观看，如果您喜欢我们的视频 Thanks very much for watching this video I hope you enjoyed it if you did please
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