ELI5: Why is fog white or gray?

Imagine you're playing with a water sprayer. When you spray it, you see tiny, tiny drops of water floating in the air, right? Fog is kind of like that, but everywhere!

Fog is made of lots and lots of really, really small water droplets or ice crystals hanging in the air, close to the ground. Think of it like a big, low cloud you can walk through.

Now, why is it white or gray? It's because of something called scattering.

• Imagine you're throwing little balls (light) at a bunch of tiny pinatas (water droplets).

• Each time a ball hits a pinata, it bounces off in a different direction.

• This is scattering!

• Because the water droplets are about the same size as the wavelength of light, all colors of light are scattered equally.

• When you mix all the colors of light together, you get white light!

Sometimes, if the fog is very thick or if there's a lot of pollution, it can look gray. This is because some of the light is being blocked or absorbed by the extra stuff in the air. Think of it as having more pinatas, so some balls don't even make it through to bounce around!