Written by Su Chengyu
Previously, a severe storm swept through South Dakota, USASioux Falls, the sky turned a strange apocalyptic green.
Many people posted photos of the "green" Amaterasu on the Internet, and those who didn't know thought the end was coming.
Why is there a green sky?
The sky has color because it is not completely "pure" and there are many tiny dusts floating in the air. Ice crystals, water droplets, etc. Because of the existence of these "impurities", sunlight will be scattered by the "impurities" when it penetrates the atmosphere and hits the ground.
If the sky is clear and there are not many particles in the atmosphere (the diameter of the gas molecules is much smaller than the wavelength of light, Rayleigh scattering occurs ), is relatively pure and is conducive to the scattering of short-wave light, so the shorter wavelength blue light and violet light in sunlight are easily scattered through the atmosphere and spread over the entire sky background. Since the human eye is not very sensitive to violet light, the sky looks It became blue.
If there is no atmosphere in the sky and these "impurities", there will be no scattering. Then during the day, you can Outside of the scorching sun, the sky background is completely dark.
Green skies are much rarer than the common blue skies. Of course, it was also caused by scattering, but the weather was before a storm, and the scattering medium was different from the tiny impurities in the blue sky. It was ice particles and water droplets.
The water droplets and ice particles in the storm are extremely dense, almost connected into one piece, blue light and some green light, the light waves are relatively Short, poor penetration, prone to scattering. At this time, the water droplets and ice droplets in the storm are blue, as shown below:
And the sun must be just setting in the west at this time. The sunset on the horizon is not blocked by clouds and scatters the sunset. Yellow, the blue of water droplets and ice droplets combined with the yellow of the sunset makes the sky look green.
"GreenSky" is naturally not a good omen. After all, there are a lot of water droplets and ice particles inside, which means heavy rain. Or hail weather is coming.
This reminds people of the blood-red sky that appeared in Zhoushan in May this year. At around 8 pm on May 7, many people took photos of the magical scene of a sky full of red light in Zhoushan, Zhejiang Province.
There were different opinions at the time, but in the final analysis it can be explained by the scattering of light. At that time, there was heavy fog in Zhoushan, and the air was Filled with water droplets.
At this time, anchored in Zhoushan was an ocean-going ship fishing for northern saury. In order to catch saury, A red "fish gathering light" will be used, and the saury will swim along with the red light source.
The stronger the light source, the easier it is to catch a large number of saury, so fishing boats emit strong and bright red light. And because this is an ocean-going ship that is about to go out to sea, the equipment was tested before that, including a red-light fish gathering light.
It happened to be a heavy fog that day, and the ocean-going ship happened to be going out to sea. The red light shone in the fog composed of water droplets, scattering the concentrated light source, allowing The sky turned blood red.
A few days later, blood-red skies also appeared in Fuzhou. On the same day, there were also offshore fishing boats. There are also foggy weather.
In fact, whether it is the apocalyptic green sky of Sioux Falls or the blood-red sky of Zhoushan, It can be explained by optical principles based on the environmental conditions at the time. However, it is still difficult to stop everyone’s various theisms...
The reproduced content only represents the author’s opinion< br>
Does not represent the position of the Institute of Physics, Chinese Academy of Sciences
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Original title: "The sky in the United States has turned strange green. Is it the end of the world?"
Source: Bringing Science Home
Editor: Lezi Superman
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