The sky appears blue to human observers because blue light from the sun is scattered in all directions by the gases and particles in the Earth’s atmosphere.
This scattering causes the direct sunlight to appear white, but the sky to take on a blue hue. The phenomenon is known as Rayleigh scattering, named after the British scientist Lord Rayleigh who first described the effect in the late 19th century.
The reason why the sky appears blue during the day and red during sunrise and sunset is also due to the scattering of light by the atmosphere. The sun’s light is more likely to be scattered by the air when it travels through the atmosphere at a low angle.
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