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Why Rainbows Are Curved?
为什么彩虹是弯曲的？
To see why rainbows are curved, it helps to understand what causes them in the first place.
要明白彩虹为什么是弯曲的，首先要知道彩虹是怎么形成的。
We see rainbows when rain is falling in front of us and the sun is shining behind us.
下雨时，背对着太阳，我们就会看见彩虹。
When sunlight enters raindrops most of it passes straight through.
当光线射进雨滴时，大多数光线会直接穿过雨滴。
But some of the light strikes the drop at such an angle that it's separated into the rainbow colors and reflected back out the front of the drop.
但是以一定角度射入雨滴的光线，会发生色散，形成不同颜色的光线。折射光线又在雨滴的背面发生反射。
Each color is reflected at a slightly different angle, but all between forty and forty-two degrees.
每一种颜色的光线亦以不同的角度反射。反射角度有细微差别，但均在40至42度范围内。
The narrow range of angles at which the colors are reflected is the key to why rainbows must the curved.
彩虹弯曲的关键在于不同颜色光线的反射角度。
The next time you see a rainbow notice that you are in the center of the arc, and that if you move the rainbow moves with you.
下次看见彩虹，注意一下，你就会发现你处在圆弧中心的位置。
This is because even though all the raindrops out there are reflecting rainbow colors, they do so in very narrow beams.
这是因为即使所有的雨滴都反射光线，但是都是以极其狭窄的光束为单位进行。
You see the colors from only those drops whose beams shine on you.
只有经雨滴反射的光束射入你的眼睛，你才会看见彩色的光。
The only shape that will allow the light beams to shine on you at the precise angles is an arc or a circle with you at the center so that you are always the same distance and angle from any point on the arc.
把所有以一定角度射入眼球的光线连接起来，只能形成圆弧或者是以你为中心的圆圈。因此你与弧形上任何一点总是保持着同样的距离。
