Origin: From the Old English word sceadan, meaning "to separate" or "to shed."
Modern Meaning: To cause something to move in many different directions at once.
In physics, scattering is what happens when light hits a tiny obstacle and gets thrown in every direction!
Light travels in a straight line until it hits something very small—like a gas molecule or a dust particle in the air. When this happens, the light is absorbed and then immediately re-emitted (shot out) in all directions.
Blue light has a short wavelength. These "small" waves hit gas molecules easily and scatter in every direction. This fills the sky with blue.
When the sun is low, light travels through more air. The blue is scattered away, leaving only the long red waves to reach you.
Mind-Blowing Fact: Without an atmosphere to scatter light, the sky would look black even during the day! This is exactly how the sky looks to astronauts on the Moon.
If small molecules scatter blue light, why don't clouds look blue? This is because of the size of the obstacles.
Clouds are made of water droplets that are much larger than gas molecules. These larger droplets are big enough to scatter all colors of light equally. When you mix all colors of the rainbow together equally, the result is white light!
However, if a cloud becomes very thick, it absorbs more light than it scatters, which is why storm clouds look dark grey from the bottom.