Eli5: If water is transparent, why are clouds white?


Eli5: If water is transparent, why are clouds white?

In: 2742

Because transparent things in tiny bits look white. Whenever light enters or exits a droplet, it changes direction. When it has to go through billions of droplets, it changes directions so many times that it’s essentially being randomly scattered, which is the same thing that white objects do to incoming light. It’s the same reason snow is white while ice is clear.

Clouds are white because they are made up of tiny droplets of water or ice crystals that scatter light in all directions. This is known as the Tyndall effect, and it causes the clouds to appear white to our eyes.

Tyndall effect is a phenomenon that occurs when light passes through a mixture of substances, such as water and air. The light is scattered by the tiny particles within the mixture, causing the light to appear different.

In the case of clouds, the Tyndall effect causes the light to be scattered by the tiny droplets of water or ice crystals that make up the clouds. This scattering causes the clouds to appear white to our eyes. The same effect can be observed when a beam of light passes through a glass of water, the beam of light appears to be scattered and the water looks cloudy.

It’s also important to note that the Tyndall effect is not limited to clouds, but can be observed in other natural phenomena such as the blue color of the sky and the brown color of the smog.

Additionally, the sun is reflecting off the clouds, making them appear white.

It’s also important to note that clouds can also appear gray, depending on their density and the amount of light they are reflecting.

Saran wrap is transparent.
Now crumple a bunch of it up into a ball.
It will now look white.

A saran wrap ball, much like a cloud, has a lot of surfaces in it.
It’s not just a solid ball: it’s got tiny (sometimes microscopic) pockets of air.
Light goes through it, comes back out, has to go through it again, come back out again.
That makes it much less transparent than if it were just a solid mass.

Similarly, with clouds, they’re not just solid water.
They’re tiny little droplets of water with air gaps between them, so light has many surfaces to pass through.

When light hits the object, it can either be absorbed, reflected, or pass through (in which case it is refracted, i.e. changes direction).

Depending on type of medium, all 3 can happen at varying degrees. When light hits water, a little bit gets absorbed because water is not 100% transparent, some of it gets reflected, and some of it passes through and gets refracted.

Since water in the clouds is not a straight wall of water, but rather tiny droplets scattered all over the place, light reflects and refracts in random directions, so you completely lose the picture of whatever is on the other side of that cloud.

Because it’s not a cloud of water, it’s water vapor, tiny droplets. When light hits a mist of tiny droplets, the light scatters.