ELI5: If water is clear, why are clouds white?

Clouds look white because they are made of trillions of tiny water drops that bounce all colors of sunlight in every direction, and when all colors of light mix together, they look white.

Think of sunlight as a bright beam that actually contains every color of the rainbow mixed together. When that light travels through a single glass of water, it passes straight through without any trouble, which is why the water looks completely clear.

However, a cloud is not a big bucket of water. Instead, it is made of billions of microscopic water droplets floating close together in the sky. When sunlight hits a cloud, something different happens:

• Bouncing light: The sunbeam hits the first tiny water drop and bounces off it.
• Scattering: That bounced light immediately hits another drop, and another, and another, bouncing around like a silver ball inside a pinball machine. This ping-pong effect is called scattering.
• Mixing colors: Because the water drops are the right size, they bounce all the rainbow colors of sunlight equally.
• The white result: When your eyes see all those colors bounced back to you at the very same time, your brain blends them together and sees the color white.

• Crushed ice: A solid ice cube is clear, but if you crush it into tiny pieces with a blender, it looks white like a snow cone.
• Soap bubbles: Water and dish soap are both clear, but when you whip them into a foamy bubble bath, the bubbles look bright white.
• Sugar and salt: A single grain of sugar looks like a tiny clear crystal, but a whole spoonful looks solid white.