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"Why is the sky blue?" is, like, the classic curious-kid question. People wonder about it all the time.
"为什么天空是蓝色的？”这是一个典型的好奇宝宝问题。是人们一直都想了解的问题。
But for all those people asking why the sky is blue, for some reason you don't get too many questions about why the ocean is blue.
只是那些问天空为什么是蓝色的人却不常问海洋为什么是蓝色的。
Maybe that's because the ocean sits under the sky. So you might just assume that the oceans look blue because they reflect the sky.
也许这是因为海洋在天空的下方。所以，人们就假设蓝色的海洋是因为海洋倒映出天空的颜色。
But if science has taught us anything, it's that just because something seems obvious, that doesn't mean it's true — like in this case.
如果说科学教会我们一点什么的话，那就是显而易见的东西并不意味着真实——比如，海洋。
Because the real reason the ocean is blue has more to do with the fact that water is just … inherently blue.
因为海洋呈蓝色的真实原因与水固有的蓝色有着很大的关系。
The sky is blue because of Rayleigh scattering, where bluer light bounces off air molecules better than redder light.
天空的蓝色是因为瑞利散射，蓝色的光比红色的光更容易反射空气分子。
And some of that blue does reflect off the ocean's surface, but that's not the main reason the ocean is blue.
并且一些蓝光确实会反射到海洋表面，但是这并不是海洋呈蓝色的原因。
The ocean is blue mostly from absorbing light, not from reflecting it. Different types of light can make water molecules vibrate different ways.
海洋的蓝色更多地是来源于吸收的光而不是反射的光。不同的光会使水分子以不同的方式震动。
When light, like from the sun, hits water, light on the redder side of the spectrum has just enough energy to get those molecules wiggling.
当来自太阳的光射入水中，红色光谱面的光将获得充足的能量使这些分子了摆动起来。
So water absorbs red, yellow, and green light better than blue.
因此相比蓝光，水能更好地吸收红、黄和绿光。
Most water molecules can't do much with blue light, though, so it basically just goes right on by.
大多数水分子与蓝光没啥联系，因此，蓝光主要只是负责正常运转。
A small amount of water, like in a cup, might look like it lets every color through equally well, since it's transparent.
似乎每种颜色都能穿透一杯水，因为水是透明的。
But that cup of water actually lets slightly more blue light through than red.
但是这一杯水中穿透的蓝光比红光要稍微多那么一点点。
And in the ocean, by the time you get to about a hundred meters deep, almost all of the red light has been absorbed, so the water is a deep blue color.
在海洋之中，一旦深入约100米时，几乎所有的红光都会被吸收，因此，海洋是呈深蓝色的。
Water still absorbs some blue light, though, which is why the oceans are completely dark below about a kilometer deep.
水仍然会吸收一些蓝光，因此千米以下的海洋深不见光。
Some blue light also gets reflected back toward the surface instead of absorbed on its way down, giving the Earth its beautiful blue oceans.
一些没有被吸收的蓝光也会反射回表面，这才赋予了地球漂亮的蓝色海洋。
There are some places with water that's a different color — it might be blue-green, for example, because of algae that reflects green light.
有一些地方的水有着不同的颜色，比如，蓝绿色，这是因为海藻反射了绿色的光。
And near mouths of big rivers, the ocean can look brown because of all the dirt and silt in the river.
在靠近大河的河口处，海洋看起来是棕色，因为河流中有泥土和淤泥。
But no matter what's in it, deep water looks pretty blue, because that's the only color of sunlight left after the other colors were absorbed.
但是不论其中有什么，深层水都是蓝色的，因为当其中一种颜色被吸收后，另一种阳光的颜色是唯一留存下来的颜色。
Some animals have even evolved to take advantage of this by being red instead of blue.
一些动物进化后，也利用了这一特点，它们身体呈现红色而非蓝色。
Blue animals in deep water will reflect that blue light, so they'll be easier for predators to find — or for prey to avoid.
一些深水蓝色动物会反射蓝光，因此它们更容易被捕食者发现，而被捕食者也能更容易避开它们。
But with little to no red light to reflect off of red animals, animals with red skin or scales or whatever just look black in deeper water, which makes them harder to find.
对于几乎很少或不反射红光的红色动物来说，它们有着红色的皮肤或鱼鳞，在深水中呈黑色，因此很难发现它们。
So, no matter what the sky looks like today, just remember that deep water is always blue.
不论如今天空呈什么颜色，只要记住深海永远是蓝色的。
Thanks to Patreon patrons Arraffa Piédiferro and someone who just put their name as a pair of brackets for asking this question,
谢谢Patreon的观众Arraffa Piédiferro以及括号里的那些观众，
and thanks to all our patrons, who keep these answers coming.
谢谢所有的不断提问的观众。
If you'd like to submit a question to be answered, you can go to patreon.com/scishow. And don't forget to go to youtube.com/scishow and subscribe!
如果你想提问，请登录patreon.com/scishow。不要忘记去youtube.com/scishow订阅我们哟~
