要获得夜光云，你需要的气温要比我们在那里看到的平均温度冷约20度绝对温度。
"To get the noctilucent clouds you need temperatures that are about 20 degrees Kelvin colder than what we see on average up there," Wickwar said.
最近在各种纬度进行的夜光云观察，提供了了解天上发生着什么的特别动力。
The recent observations of noctilucent clouds at all kinds of latitudes provide an extra impetus to understand what is going on up there.
通过测量夜光云反射的光的变化，他们发现夜光云从盛到衰的周期大约为27天。
By measuring changes in the light reflected from the clouds, they found that the clouds appear to wax and wane in prevalence over a 27-day cycle.
利用拉塞尔NASA项目获得的数据绘制的夜光云效果图。
Captured by flickr user, breff 3. A rendering of the noctilucent clouds created from data obtained by Russel’s NASA project, AIM.
以下可以对比自然形成的夜光云看起来来是怎样的
Here's what a naturally-occuring noctilucent cloud looks like, for comparison
奥哈马、巴黎、西雅图和其它地区的摄影师及天空观察家们跑到野外去捕捉夜晚发光的云，科学家们称其为“夜光云”（noctilucent cloud)。
Photographers and other sky watchers in Omaha, Paris, Seattle, and other locations have run outside to capture images of what scientists call noctilucent (”night shining”) clouds.
这些云也被称为“noctilucent”，也就是“夜光云”，因为他们一般出现在黄昏时分。
The clouds are also called noctilucent, or "night-shining," clouds because they are usually seen at twilight.
极地中层云也被称为夜光云层（noctilucent）（就是在夜晚还闪光的云）。这一特点在这张太空照片上显露无疑。
Polar mesospheric clouds are also known as noctilucent or “night-shining” clouds—a property that is clearly visible in this astronaut photograph.
到了观看极地中气层云的时候，在太空中使用高β角度，我们能捕捉到日落时刻这层薄薄的夜光云。
It is the season for viewing Polar Mesospheric Clouds, and with our high beta-angle we were able to capture this thin layer of noctilucent clouds at sunset (6-25-2010).
利用拉塞尔NASA项目获得的数据绘制的夜光云效果图。
The sky over Omaha on July 14th, snapped by Mike Hollingshead at Extreme Instability 2. A rendering of the noctilucent clouds created from data obtained by Russel’s NASA project, AIM.
我们还不清楚它们为什么会从极地迁移下来，也不知道在过去的二十五年里，为什么极地地区出现越来越多的夜光云，而且光芒更灿烂。
Or why, over the last 25 years, more of them are appearing in the polar regions, too, and shining more brightly.
尽管我们认为夜光云由裹着冰的小微粒组成，但仍有许多未知有待研究。
Although noctilucent clouds are thought to be composed of small ice-coated particles, much remains unknown about them.
最近有线索表明，至少部分夜光云是由航天飞机上排出的水蒸气结冰所导致的。
Recent evidence indicates that at least some noctilucent clouds result from freezing water exhaust from Space Shuttles.
下图拍摄于本月上旬，图中是夜幕降临后，网状的夜光云给加拿大阿尔伯达省埃德蒙顿的夜空织出的奇异景色。
Pictured above earlier this month, a network of noctilucent clouds cast an eerie white glow after dusk, above the the city of Edmonton, in Alberta, Canada.
下图拍摄于本月上旬，图中是夜幕降临后，网状的夜光云给加拿大阿尔伯达省埃德蒙顿的夜空织出的奇异景色。
Pictured above earlier this month, a network of noctilucent clouds cast an eerie white glow after dusk, above the the city of Edmonton, in Alberta, Canada.
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