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Why Rainbows Are Curved?
為什么彩虹是彎曲的？
To see why rainbows are curved, it helps to understand what causes them in the first place.
要明白彩虹為什么是彎曲的，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.
下雨時，背對著太陽，我們就會看見彩虹。
When sunlight enters raindrops most of it passes straight through.
當光線射進雨滴時，大多數光線會直接穿過雨滴。
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線，會發生色散，形成不同顏色的光線。折射光線又在雨滴的背面發生反射。
Each color is reflected at a slightly different angle, but all between forty and forty-two degrees.
每一種顏色的光線亦以不同的角度反射。反射角度有細微差別，但均在40至42度范圍內。
The narrow range of angles at which the colors are reflected is the key to why rainbows must the curved.
彩虹彎曲的關鍵在于不同顏色光線的反射角度。
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.
下次看見彩虹，注意一下，你就會發現你處在圓弧中心的位置。
This is because even though all the raindrops out there are reflecting rainbow colors, they do so in very narrow beams.
這是因為即使所有的雨滴都反射光線，但是都是以極其狹窄的光束為單位進行。
You see the colors from only those drops whose beams shine on you.
只有經雨滴反射的光束射入你的眼睛，你才會看見彩色的光。
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線連接起來，只能形成圓弧或者是以你為中心的圓圈。因此你與弧形上任何一點總是保持著同樣的距離。
