Here's why:

* Planets orbit a star: Planets are celestial bodies that orbit a star. The Sun is the star at the center of our solar system. It's not orbiting anything.

* Planets are much smaller than stars: Stars are massive balls of hot gas that produce light and heat through nuclear fusion. Planets are significantly smaller and do not have the same internal processes as stars.

* Planets don't produce their own light: Planets reflect light from the star they orbit. The Sun, on the other hand, is a giant furnace that generates its own light and heat.

The Sun is classified as a star, and it's the largest and most massive object in our solar system.