In the record of his life at Walden Pond, Henry David Thoreau reported on an odd phenomenon. "As I walked on the railroad causeway," he wrote, "I used to wonder at the halo of light around my shadow." Thoreau was probably seeing a phenomenon called "heiligenshein," which is German for halo. This is a glowing light around the head and shoulders of your shadow. These days, it's likely to be seen by early morning golfers on dewy grass. Where does this halo come from?
在瓦尔登湖的生活记录里，亨利·大卫·梭罗报告了一个奇怪的现象。“而当我在铁路堤道上行走的时候，”他写道：“我常常惊奇地看到我的影子周围有一个光轮。”梭罗可能看到的是一个叫作"heiligenshein"的现象，"heiligenshein"是德语，意为“光环”。那是围绕在头和肩膀的影子周围的一圈耀眼的光芒。这些天，清晨在被露水打湿的高尔夫球场上很有可能看见这种现象。这些光环来自哪里？
Your shadow's halo is made by something called "back scattering." This happens whenever sunlight enters a dewdrop. The sunbeam enters the front of the drop, then a certain amount of light bounces off the back. This light streams back out the front, almost exactly in the direction it came from. Thanks to back scattering, every dewdrop on the golf course is shining a narrow beam of light directly back toward the sun.
影子周围的光环是由于“反向散射”形成的。当阳光射进水滴时，往往会发生这种现象。阳光从水滴前方进入时，总有一定数量的光线被反射回去。这些光线从水滴前方反射回去，反射角度几乎与入射方向一样。由于反向散射，高尔夫球场上的每一滴露珠都会向太阳发出一道狭小的光芒。
Heiligenshein is the glare from this backward bouncing sunlight. If every dewdrop bounces sunlight, why does the halo only appear around your shadow's head instead of over the whole fairway? Unlike a light bulb, which shines light in every direction, each dewdrop is reflecting a narrow, tightly focused beam, aimed directly at the sun. Your eyes must be in the path of these beams to see them. If you're looking down at your shadow, your eyes are only in the line of fire for those dewdrops near your shadow's head. The beams from the dewdrops a few feet to the side miss your eyes entirely. This is why you're likely to see a halo around your own shadow's head, but not around those of others.
Heiligenshein 就是这种反射光线较耀眼的部分。如果每一滴露水都反射阳光，那么为什么光环只出现在头部的影子周围？灯泡向四面八方发光，但与灯泡不同的是，露水反射的光只对着太阳，而且反射光线即狭小又集中。只有当这些光束射入你的眼睛，你才能看见。当你低头看向影子时，只有影子头部周围的露珠反射的光线才会进入你的眼睛，而旁边几英尺远的露珠反射的光芒就会错过。这就是为什么你可能在影子头部周围看到光环，而不是在影子的其它部位看到。
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