Answer · confidence: strong
Why is the sky so blue when the air is clear, not dusty?
Research question: What is the fundamental difference between Rayleigh scattering and Mie scattering, and why does the former dominate in clear skies?
The fundamental difference is that Rayleigh scattering occurs when particles are much smaller than the wavelength of light, while Mie scattering applies when particle sizes are comparable to the wavelength 6. Rayleigh scattering intensity is strongly dependent on wavelength, scattering shorter blue wavelengths much more than red ones, whereas Mie scattering is roughly independent of wavelength 78. Rayleigh scattering dominates in clear skies because the air molecules are very small, causing the blue color of the sky at large angles to the sun 14.
Checked 2026-10-10. Only documented and supported facts are used.
Dig deeper on this questionSources
[1] supported
Rayleigh scattering applies specifically when the scattering particle is very small, with a size less than 1/10 of the wavelength, causing the whole surface to re-radiate with the same phase.
"Rayleigh scattering applies to the case when the scattering particle is very small (x ≪ 1, with a particle size < 1/10 of wavelength [ 10 ] ) and the whole surface re-radiates with the same phase."Rayleigh scattering
[2] supported
In Rayleigh scattering, the intensity of scattered light is proportional to the inverse fourth power of the wavelength and the sixth power of the particle size.
"it is incoherent and the resulting intensity is just the sum of the squares of the amplitudes from each particle and therefore proportional to the inverse fourth power of the wavelength and the sixth power of its size."Rayleigh scattering
[3] supported
Mie scattering involves interference effects that develop through phase variations over the object's surface when the size parameter is intermediate (x ≃ 1).
"he intermediate x ≃ 1 of Mie scattering , interference effects develop through phase variations over the object's surface."Rayleigh scattering
[4] supported
Rayleigh scattering causes the blue color of the sky at large angles to the direction of solar rays and yellow or orange colors for light from the direction of the Sun.
"Rayleigh scattering causes the blue color of the sky at large angles to the direction of solar rays and yellow or orange colors for light from the direction of the Sun."Rayleigh scattering
[5] supported
The amount of scattering in Rayleigh scattering is inversely proportional to the fourth power of the wavelength, meaning blue light is scattered much more than red light.
"the amount of scattering is inversely proportional to the fourth power of the wavelength (e.g., a blue color is scattered much more than a red color as light propagates through air)."Rayleigh scattering
[6] supported
Rayleigh scattering describes light scattering by particles much smaller than the wavelength, whereas Mie scattering applies when particle sizes are comparable to the wavelength.
"Rayleigh scattering describes the elastic scattering of light by spheres that are much smaller than the wavelength of light. ... Mie scattering (sometimes referred to as a non-molecular scattering or aerosol particle scattering ) takes place in the lower 4,500 m (15,000 ft) of the atmosphere , where many essentially spherical particles with diameters approximately equal to the wavelength of the in"Mie scattering
[7] supported
Rayleigh scattering intensity is strongly dependent on wavelength, being much greater for shorter wavelengths like blue light, which causes the blue color of the sky.
"The blue colour of the sky results from Rayleigh scattering, as the size of the gas particles in the atmosphere is much smaller than the wavelength of visible light. Rayleigh scattering is much greater for blue light than for other colours due to its shorter wavelength."Mie scattering
[8] supported
Mie scattering is roughly independent of wavelength and scatters light more strongly in the forward direction than in the reverse direction.
"It can be shown, however, that scattering in this range of particle sizes differs from Rayleigh scattering in several respects: it is roughly independent of wavelength and it is larger in the forward direction than in the reverse direction."Mie scattering
[9] supported
The Rayleigh scattering model breaks down when particle size exceeds approximately 10% of the incident radiation's wavelength.
"The Rayleigh scattering model breaks down when the particle size becomes larger than around 10% of the wavelength of the incident radiation."Mie scattering
[10] supported
Clouds appear white or grey because water droplets are comparable in size to visible light wavelengths, causing Mie scattering that affects all wavelengths approximately identically.
"In contrast, the water droplets that make up clouds are of a comparable size to the wavelengths in visible light, and the scattering is described by Mie's model rather than that of Rayleigh. Here, all wavelengths of visible light are scattered approximately identically, and the clouds therefore appear to be white or grey."Mie scattering