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Sky brightness refers to the visual perception of the sky and how it scatters and diffuses light. The fact that the sky is not completely dark at night is easily visible. If light sources (e.g. the Moon and light pollution ) were removed from the night sky , only direct starlight would be visible.
Scattering effects also partially polarize light from the sky and are most pronounced at an angle 90° from the Sun. Scattered light from the horizon travels through as much as 38 times the air mass as does light from the zenith, causing a blue gradient looking vivid at the zenith and pale near the horizon. [9]
A colorful sky is often due to indirect sunlight being scattered off air molecules and particulates, like smog, soot, and cloud droplets, as shown in this photo of a sunset during the October 2007 California wildfires. Atmospheric optics is "the study of the optical characteristics of the atmosphere or products of atmospheric processes ....
In this band, degrees of polarization near 80% are typically reached. Degree of polarization in the Rayleigh sky at sunset or sunrise. The zenith is at the center of the graph. When the Sun is located at the zenith, the band of maximal polarization wraps around the horizon. Light from the sky is polarized horizontally along the horizon.
On the horizon, refraction is slightly greater than the apparent diameter of the Sun, so when the bottom of the sun's disc appears to touch the horizon, the sun's true altitude is negative. If the atmosphere suddenly vanished at this moment, one couldn't see the sun, as it would be entirely below the horizon.
This is why the sky looks blue; you are seeing scattered blue light. This is also why sunsets are red. Because the Sun is close to the horizon, the Sun's rays pass through more atmosphere than normal before reaching your eye. Much of the blue light has been scattered out, leaving the red light in a sunset.
"This is why the sky appears blue on a nice sunny day with the sun high in the sky," Rossio said. ... the angle of the sun in the horizon yields more atmosphere and aerosols for which the light ...
Scheme of light pillars formation. Since they are caused by the interaction of light with ice crystals, light pillars belong to the family of halos.The crystals responsible for light pillars usually consist of flat, hexagonal plates, which tend to orient themselves more or less horizontally as they fall through the air.