Here's why:

* Clouds are made of water vapor or ice crystals. The Sun is much too hot for water to exist in any form.

* The Sun is a giant ball of hot gas. It's mostly made of hydrogen and helium, constantly undergoing nuclear fusion, which produces light and heat.

* Clouds are found in the atmosphere of planets. The Sun doesn't have an atmosphere in the way that Earth does.

So, while clouds and the Sun are both in the sky, they are very different things!