How far can people see the sky at the farthest of the naked eye?

You look up and look up, can you see the sun? The sun is about 150 million kilometers away from us. You look at the starry sky last night. Can you see the cowherd star and the weaver actress? That is not a galaxy at all. So people can see the distance of the light grade with the naked eye.

Of course, this is looking up. The height of the atmosphere is limited. In the case of clear the weather, the light of the stars can be seen through the atmosphere, and you can naturally see it. But when you look at it, you need to look at the air quality of the atmosphere, so there is a concept of visibility in meteorology.

Visibility refers to the maximum distance that people with normal vision can recognize the target from the background. This is actually a very subjective indicator. The visibility obtained by different people may be different. Therefore, the value of visibility has never been absolute. Visibility depends on the current meteorological environment. Fog, haze, sand, dust and even rain and snow will cause visibility. Usually we measure visibility are manual measurement and equipment measurement. Artificial observation visibility generally refers to effective level visibility. Effective level visibility refers to the maximum horizontal distance of the target that can be seen in the range of more than one -half of the field of vision. At present, most meteorological stations use equipment measurement, but in the weather such as floating dust and sand, manual measurement is more accurate. The visibility of equipment measurement is represented by meteorological optical vision. Meteorological optical vision refers to the optical flux of parallel beams with a high temperature of 2700k in incandescent light, which weakens the path length of the path passed by 5%of the initial value in the atmosphere.

When I return to the question, how far can people with normal vision be seen? In the case of clear the weather, the visibility can reach 20 kilometers to 30 kilometers. In the polar place where the air is very clean, humans can see things other than 70 kilometers away. This is the source of "Wangshan running to death". Under normal circumstances, people can really see far.

Reference materials:

[Popularization reading] Scientific understanding visibility and observation

By Frost Bai

Q.e.d.

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