Here's why:

* Stars produce their own light and heat through nuclear fusion. The Earth does not do this. It gets its light and heat from the Sun.

* Stars are much larger than planets. The Earth is about 12,742 kilometers in diameter, while even the smallest stars are much larger.

* Stars are made up mostly of hydrogen and helium. The Earth is made up of a variety of elements, including iron, oxygen, and silicon.

Let me know if you have more questions about stars or planets!