A Hertzsprung-Russell Diagram, to showcase the different types of stars.

A star is a celestial body that is in hydrostatic equilibrium (i.e. spherical under the force of gravity) and is undergoing or has underwent nuclear fusion. Many stars are surrounded by orbiting planets; the star-planet collection is called a star system. Some stars come in gravitationally bound groups of two or more; these are called multiple star systems.

A civilization that controls all of the available resources of a star, such as by surrounding it with a Dyson sphere, is called a Type 2.0 Civilization.

Stellar Classes
Ω · N · D · Y · T · L · M · K · G · F · A · B · O
Stellar Luminosity Classes
0 · I · II · III · IV · V · VI · VII