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In areas like the central United States that get lots of tornados, there's a common piece of celestial fortunetelling.
在龙卷风常有发生的美国中部地区，常有一种带有神话色彩的占卜。
People say that green skies mean a tornado is on its way.
人们说绿色的天空意味着一场龙卷风即将到来。
Research has shown that it isn't quite as simple as that
研究表明真相并没有那么简单
but scientists have found that if you see a green sky, you should probably go inside.
但是科学家发现，如果你看到天空是蓝色的，那么或许你应该躲进屋子了。
As far as most scientists can tell the green skies around powerful thunderstorms
据科学家所说，雷暴周围的绿色天空
are usually a combination of red sunsets and water droplets.
常是红色日落和水滴的结合。
Like we've talked about before,
如我们之前所说，
daytime skies are blue because blue or shorter wavelengths visible light
白天的空天是蓝色的，因为蓝色或较短的波长可见光
tends to bounce off air molecules better than red or longer wavelength light.
比红色或更长的波长光更善于反弹空气分子。
So the blue light gets bounced all over the sky and looks like it's coming from everywhere.
所以蓝光在空中到处反弹，看上去到处都是蓝光。
Meanwhile, around sunset, sunlight travels through so much atmosphere
同时，日落时分，阳光穿过大量大气
that just about all the blue is bounced away from the horizon,
几乎所有蓝光都从地平线上反弹而出，
leaving all those picturesque reds and oranges behind.
只留下所有那些鲜艳的红色和橙色。
But that quick summary hides something important.
但是这种简短的总结隐藏了一些重要的东西。
Sunsets might look exclusively red and orange
日落可能看起来只有红色和橙色
but there's still some green and even blue light hidden in there just far less than the other colors.
但是其中还有一些绿色，甚至有蓝色光线隐藏其中，只是那其他颜色那么显眼。
But for us to notice the residual green light, it needs to hit something that reflects green light much better than red.
但是如果我们想要看到残留的绿光，需要一些能够更好的反射绿光而非红光的事物。
That's where water comes in.
所以我们还需要水。
Big, tall, threatening storm clouds are made of water droplets and even though water is best at reflecting blue light,
巨大且可怕的乌云是由水滴组成，虽然水最善于反射蓝光，
it can still reflect green pretty well much better than reds and oranges.
但是相比红光和橙色光，水仍然可以很好的反射绿光。
So under just the right conditions,
因此只要在正确的条件下，
the water in and around a cloud can bounce the green light hidden in the sunset right into our eyes, making the sky look green.
云层之中和周围的水可以将隐藏在日落中的绿光反射至我们的眼睛里，所以在我们看来，天空就是绿色的。
This explains why most of these eerie skies are reported late in the day when there's not much blue light around a dominate.
这也就解释了为什么怪异的天空多数出现在没有蓝光的日子里。
Of course, green skies can happen in the middle of the day too,
当然，绿色的天空也常在中午发生，
enough blue light just has to get bounced elsewhere by the right combination of air molecules above the clouds and the water within them.
云层之上空气分子的正确组合和云层中的水分，能让充足的蓝光四处反弹。
Still, none of the conditions that can turn skies green are unique to the clouds that spawn tornadoes.
对于能够孕育暴风雨的云层而言，能够将天空变为绿色的空气条件，没有一个是单独出现的。
They're often associated with these twisters
它们常和这些龙卷风相结合
because the intense storms that produce green tinted skies can also produce tornadoes but they don't always.
因为那些能制造绿色天空的猛烈暴风也能孕育出龙卷风，但也并非总是携带龙卷风。
Sometimes they just lead to lots of rain and maybe some hail.
有时它们只是产生大量雨水，或者是一些冰雹。
So if you see huge storm clouds rolling in and a green tint in the sky,
所以，如果你看到巨大的暴风云在翻滚，看到天空中的有一抹绿色，
it doesn't necessarily mean there's about to be a tornado, but it does mean you should probably head indoors.
这并不一定意味着一场龙卷风的来临，但是这确实意味着你应该躲进屋里。
Thanks for asking and thanks to all of our patrons on patreon who help us keep answering questions like this.
感谢提问，感谢一直提问的patron赞助人。
If you'd like to support the show or ask a question of your own, you can go to patreon.com/scishow
如果想支持我们的节目或是想要提问，请登录patreon.com/scishow。
