On earth, whenever the sun sets, the sky on earth will appear yellow orange or red.
In the solar system, the yellow orange sunset is not everywhere. Different planets in the solar system determine the color of the sunset. On Mars, the setting sun will be blue; on Uranus, it will change from blue to green; on Titan, it will change from orange to brown.
The atmosphere of the planet determines the color of the sunset
On the earth, the atmosphere is made up of tiny gas molecules. The main components of the earth's atmosphere are nitrogen and oxygen. The two kinds of gas molecules have different ability to scatter light.
Oxygen and nitrogen have more obvious scattering effect on the blue light in the light, while red light can travel farther in the earth's atmosphere.
At noon, the sunlight is very abundant. Although blue and purple light scatter, the light does not need to travel a long distance to reach our eyes, so we can hardly feel the effect of scattering.
But if the atmosphere is thicker or the haze is more serious, the scattering of blue and purple light will be more obvious, which is why the sky turns yellow in haze weather.
In clear weather, the sunlight scattering is not obvious, and the human eye is more sensitive to blue light, so we can see the blue sky.
In the evening, the sun began to shine on the other hemisphere, the sun is farther and farther away from us. At this time, if the sunlight wants to enter the human eye, it needs to go through a longer distance, and it will also be subject to stronger scattering.
The scattering effect increases with the distance from the sun. Blue and purple light are gradually scattered. Red and yellow light enter our eyes. At this time, the sky will appear yellow orange. Similarly, the stronger the atmospheric refraction effect is, the closer the sky is to red.
This is the principle of Rayleigh scattering, using Rayleigh scattering, we can explain the color of the sky, the color of the sunset.
The earth's atmosphere is unique:
The basis of Rayleigh scattering is that different gas molecules have different scattering ability for different wavelengths of light.
The composition of the earth's atmosphere is mainly oxygen and nitrogen, but in other planets, there may be completely different gas molecules. In Uranus, for example, the main components of the atmosphere are hydrogen, helium and methane.
Hydrogen, helium and methane molecules have strong ability to scatter blue and red light. If humans live in Uranus, they will see a bluer sky at noon (the same as the earth), and the setting sun is green.
The Martian atmosphere is only 80 / 1 of the density of the earth, so the degree of Rayleigh scattering is very low. On Mars, the sky is basically blue, whether it is day or evening.
The photos taken by the human Mars probe on Mars show that the sky on Mars is bluer than expected. This is because the Martian atmosphere is full of dust, which is different from gas molecules, and has a strong scattering effect on red light, making the blue light more obvious.
Every star or planet, as long as it has different atmospheric components, will have different sky and sunset colors.
Stars with gaseous atmosphere can often see longer wavelength colors at sunset, while stars without gas molecules in the atmosphere can only see shorter wavelength colors.
Because we often see yellow orange sunset on the earth, we will feel used to it. However, this kind of sunset is very rare in the universe~
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