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These are optical phenomena in which light rays are bent due to thermal variations in the refractive index of air, producing displaced or heavily distorted images of distant objects. Other optical phenomena associated with this include the Novaya Zemlya effect , in which the Sun has a distorted shape and rises earlier or sets later than predicted.
The Rayleigh sky model describes the observed polarization pattern of the daytime sky. Within the atmosphere, Rayleigh scattering of light by air molecules, water, dust, and aerosols causes the sky's light to have a defined polarization pattern. The same elastic scattering processes cause the sky to be blue.
The blue sky spectrum contains light at all visible wavelengths with a broad maximum around 450–485 nm, the wavelengths of the color blue. Diffuse sky radiation is solar radiation reaching the Earth 's surface after having been scattered from the direct solar beam by molecules or particulates in the atmosphere .
Rayleigh scattering causes the blue color of the daytime sky and the reddening of the Sun at sunset. Rayleigh scattering (/ ˈ r eɪ l i / RAY-lee) is the scattering or deflection of light, or other electromagnetic radiation, by particles with a size much smaller than the wavelength of the radiation.
Diagram showing displacement of the Sun's image at sunrise and sunset Comparison of inferior and superior mirages due to differing air refractive indices, n. Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height. [1]
Optical phenomena are any observable events that result from the interaction of light and matter. All optical phenomena coincide with quantum phenomena. [ 1 ] Common optical phenomena are often due to the interaction of light from the Sun or Moon with the atmosphere, clouds, water, dust, and other particulates.
Particles in the air scatter short-wavelength light (blue and green) through Rayleigh scattering much more strongly than longer-wavelength yellow and red light. Loosely, the term crepuscular rays is sometimes extended to the general phenomenon of rays of sunlight that appear to converge at a point in the sky, irrespective of time of day. [3] [4]
When the day's sky is overcast, sunlight passes through the turbidity layer of the clouds, resulting in scattered, diffuse light on the ground . This exhibits Mie scattering instead of Tyndall scattering because the cloud droplets are larger than the wavelength of the light and scatters all colors approximately equally.