Astronomy

Rayleigh effect and Mie effect

Rayleigh effect and Mie effect

Why is the sky blue? Why a beautiful reddish sunset? And a gray day? The answer is in the scattering of light and the Rayleigh and Mie effects.

Sunlight is an electromagnetic radiation composed of different wavelengths. Our eye captures only the part of light that corresponds to certain wavelength frequencies. White light is the sum of all the wavelengths we perceive.

Each color is a unique wavelength. They follow the order of the rainbow: the color red has the longest wavelength, and the violet the shortest. The scattering of light is its decomposition into colors. The wavelengths take different angles and the colors separate. The longer the wavelength, the greater the angle.

When sunlight comes into contact with the atmosphere, it disperses. Our atmosphere is formed by small particles, and the degree of humidity favors the greater diffusion of some colors compared to others.

Rayleigh Effect

Light is a form of radiation, that is, energy. When colliding with small particles in the atmosphere produces the Rayleigh effect. Some of the energy is transferred to these particles, which vibrate and diffuse the light in all directions. That is why the light fills the whole sky.

Outside the atmosphere, the sky is dark, although the sunlight comes. Short waves are the ones with the greatest diffusion. That is, violets and blues. Since white light contains more blue light than violet, blue predominates. In addition, our eye is more receptive to blue. We see the yellow Sun because we have already subtracted the blue color to the white one. And, when it is high, yellow prevails over red because its wavelength is shorter.

Mie scattering

At dusk and sunset the sun is low. The waves travel a longer path through the atmosphere. So those of short wavelength are lost and those of long wave prevail. That's why reddish colors spread. It also influences the amount of dust accumulated in the atmosphere.

The Mie effect occurs when light collides with large particles or molecules. The particles absorb part of the light and reflect the rest, like small mirrors. Here the color depends on the composition of the particle. When the atmosphere is very charged and the clouds are thick, the Mie effect is accentuated and favors gray colors.

The Mie effect dominates the atmosphere of Mars. Its sky is not blue but of a red and yellow lead. Carl Sagan describes the disappointment of the press when they showed the first photos of the sky from Mars. Nothing comparable to our beautiful blue sky.

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