Clouds don't actually "block" the sun in the way you might think, like a wall. They actually scatter the sunlight. Here's a breakdown:

* Sunlight is made of different wavelengths: Sunlight is made up of all the colors of the rainbow, each with a different wavelength.

* Cloud droplets and ice crystals: Clouds are made of tiny water droplets or ice crystals. These tiny particles are much smaller than the wavelengths of light.

* Scattering: When sunlight encounters these tiny particles, it gets scattered in all directions. This means that the light is deflected and changes direction.

* Less direct sunlight: This scattering means that less direct sunlight reaches the ground. That's why it feels cooler and dimmer on a cloudy day.

* Different colors: Blue light is scattered more easily than red light. This is why the sky appears blue on a clear day. On a cloudy day, more of the blue light gets scattered away, making the sky appear white or gray.

Think of it like this: Imagine shining a flashlight on a bowl of water. The light will be scattered in all directions, making the water appear cloudy. Similarly, sunlight is scattered by the cloud droplets, reducing the amount of direct sunlight that reaches us.

In summary: Clouds don't block the sun completely; they scatter the sunlight, making it less direct and reducing the amount of light that reaches the ground.