1. Sun
The sun is a star. A star does not have a solid surface, but is a ball of gas (hydrogen (H2) and helium (He)) held together by its own gravity. The sun is the center of our solar system and makes up 99.8% of the mass of the entire solar system. If the sun were as tall as a typical front door, Earth would be about the size of a nickel.
Sun is a only star in a Solar System.