The blue sky:
* Rayleigh scattering: Sunlight is made up of all colors of the rainbow. When sunlight enters the Earth's atmosphere, it interacts with tiny molecules of air (nitrogen and oxygen). These molecules scatter the shorter wavelengths of light (blue and violet) more strongly than the longer wavelengths (red and orange).
* Our eyes: While violet is scattered even more strongly, our eyes are more sensitive to blue light. This is why we perceive the sky as blue.
The colorful sunrise and sunset:
* Longer path: As the sun rises or sets, the sunlight has to travel through a longer path of atmosphere. This means the blue light gets scattered away more, leaving the longer wavelengths (red and orange) to reach our eyes.
* Clouds: Clouds can reflect the red and orange light back towards us, making the sky appear more colorful.
Why the sky can sometimes look white:
* Clouds: Thick clouds can block blue light, making the sky appear white.
* Pollution: Air pollution can scatter all wavelengths of light equally, making the sky appear hazy and whitish.
In summary:
The sky is not actually white, but appears blue most of the time due to the scattering of sunlight by air molecules. At sunrise and sunset, the longer path of sunlight through the atmosphere causes red and orange colors to be more prominent.
