Rayleigh Scattering
The elastic scattering of light or electromagnetic radiation by particles much smaller than the light's wavelength.
Governing formula
I_scattered ∝ 1 / λ⁴
SI unit
W/m²
In depth
Scattering intensity is inversely proportional to the fourth power of wavelength ($λ^4$). Short blue light ($~ 400 nm$) scatters nearly 10 times more effectively than longer red light ($~ 700 nm$).
Examples in the real world
The daytime sky appearing blue due to atmospheric Rayleigh scattering of solar light by $N_2$ and $O_2$ air molecules.