Eli5: If water is transparent, why are clouds white?
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If glass is transparent, why is a handful of tiny glass chips white? For the same reason. All those small particles (droplets of water in the clouds, or the glass chips) reflect light in all directions, until light has a hard time getting through, and is dispersed in all directions.
The result is a white opaque mass.
Nothing is truly “transparent”, but more properly translucent.
In other words: some but not all light passes through water.
Besides clouds, you can see large bodies of water block light. You don’t have to go very far underwater before it gets really dark!
In the case of clouds, they’re white not because they’re blocking light, but because they’re diffusing and dispersing it. Think frosted glass.
Each time you get an interface between materials like water and air or glass and air, you’ve got a place where light will bend. The drops of water in a cloud are each bending the light and scattering it, which adds up to something bright (they’re kinda white) but that also obscures your view.
Water freezes when it’s that high in the atmosphere. After water has been evaporated into the atmosphere it creates little crystalline structures that form clouds. They appear white because they refract light and all colors together are white. Think about a prism. You can see all the colors that combine to make white light through a prism. That’s why the clouds appear white.
Everything you see is just light bouncing and having different wavelengths. Your brain perceives them as colors. So basically the light hits. Same as water looks blue even though it’s transparent.
Clouds are made of droplets. Water droplets scatter light. When you have that many droplets hanging out near each other the light gets scattered so much that we perceive it as white light
You can’t just ask clouds why they’re white?
In a word- diffraction.
Basically, when lots of surfaces and angles are introduced to ray-paths of light (which implies there are different materials for the light to traverse – with the important distinction being changes in those materials’ densities), the light ‘bounces’ around instead of traveling in a straight line. Enough chaotic, criss-crossing light rays creates opaqueness – in the case of liquid water, light sees it as a single continuous material of constant density and the ray-paths pass linearly through (so that looks clear to us). In the case of clouds, which are millions droplets, the light see it as millions of discrete objects (which it physically is) and refracts each time passing through the curves droplet surfaces, redirecting the ray-path in an amount proportional to the angle relative to the surface interface & difference in material densities (this is known as Snell’s Law) – and we can’t see through the chaos.
Gretchen you can’t ask clouds why they’re white!
Also, clouds are white because light from the Sun is white. As light passes through a cloud, it interacts with the water droplets, which are much bigger than the atmospheric particles that exist in the sky.
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