What is Rayleigh scattering
Rayleigh scattering refers to the scattering of light by particles in its path of size up to one-tenth the wavelength of the light and occurs without any loss of energy or change of wavelength.
For light frequencies well below the resonance frequency of the scattering medium (normal dispersion regime), 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.
Applications
The Sun still shines at the atmosphere, but at a sharp angle beneath the horizon.
In this hour, we see the sky glow because molecules in the air scatter these sunlight in different directions, including ours.
This is also why the evening sky appears red at the horizon.
Both this effect and the sky being blue-hued in daytime is the result of Rayleigh scattering
As the Sun continues to set, a smaller amount of sunlight strikes the upper atmosphere.
Nightfall truly kicks in only when the Sun is at least around 18 degrees beneath the horizon.
The arrival of daylight happens in a similar process, in reverse.
When the Sun is at least 18 degrees below the horizon in the east, the sky starts to turn reddish again near the horizon.
When the star’s position crosses the horizon (as seen by the observer), daylight breaks out and the day begins.
COMMENTS