What makes a planet different from a star?

A star is a huge object massive enough to make energy in its core by fusing hydrogen into helium. A planet is smaller and does not make its own light; it shines only when starlight reflects from rock, ice, clouds, or gas. Our sun is a star, and Earth is a planet.

The size gap is hard to picture: more than a million Earths could fit inside the sun, and Jupiter is still far too small to start fusion. Its shine in our sky is borrowed, like a porch window catching afternoon light.