“夜光”云(‘Night shining’ clouds)

大约在每年的这个时候，一些幸运的人能够目睹这些罕见、神奇的云朵。夜光云是我们天空中最高的云，只有在夏天才能看到。它们是由在太空边缘发光的冰尘组成的，距离地球表面大约50英里。看到它们的诀窍是在黄昏时抬头仰望天空，这时太阳已经落在地球表面，但高海拔的夜光云仍在阳光下。这些云几乎只出现在高纬度地区，大约在南北50°到70°之间。
原文：
It’s around this time of year when some lucky people get to witness these rare, wondrous clouds. Known as noctilucent, or ‘night shining,’ clouds, they’re the highest clouds in our sky and are only visible during summer. They’re made up of icy dust glowing at the edge of space, roughly 50 miles above the planet’s surface. The trick to seeing them is to gaze up into the sky at twilight, when the sun has already set on the Earth’s surface, but the high-altitude noctilucent cloud is still in sunlight. These clouds occur almost exclusively at high latitudes, roughly between about 50° and 70° North or South.
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