5. 怪异云层的形成（Weird Cloud Formations）
Last October, footage of a giant halo in an overcast sky over Moscow surfaced on YouTube. The video had everything needed to ignite UFO rumors. It's grainy. At one point, a dark pointy object appears to bolt out of the ring. There's even a panicked-sounding Russian radio broadcast in the background.
今年10月份，莫斯科阴天上空的巨大光环的连续镜头浮现在视频网站上。视频具有可以用来谣传UFO所需要的一切。它是有条有理的。在某一时刻，一个模糊、尖尖目标似乎要匆忙地离开了这个环状物。在视频的背景上，甚至还有个惊慌音响的俄罗斯广播电台。
Cool-headed meteorologists were quick to put the story to bed: It was just an optical illusion, the cause of sunlight hitting a cloud disturbed by wind or plane traffic in just the right way. Most likely it was what is known as a hole-punch cloud. These occur in cirrus or cirrostratus clouds, which are often composed of ice crystals and super-cooled water droplets – water that is below freezing temperature, but still in liquid form. The physical properties that hold these clouds together are delicate, and when disturbed – by a jet plane, wind or even cloud seeding efforts – the droplets can freeze instantly or evaporate, the latter of which will form the hole.
头脑冷静的气象学家很快把这件事搁置起来：认为它只是一种光的幻觉，起因于阳光击中了一朵云彩，刚好能以一种合适的方式被风或飞机交通而使人感到不安。最有可能的是所谓冲孔云。这些云层发生在卷云或卷层云，它们通常包含着冰晶和过冷的水滴——温度低于冻结温度却依然能保持着其液体的状态。把云层聚合在一起的物理性质是很微妙的，当它们受到扰动的时候——喷气式飞机、风，甚至是云种散播效应——水滴就可能会立即冻结或蒸发，如果是后者就会形成洞眼。
