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

A star is a celestial body that is in hydrostatic equilibrium (in other words 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
Y · T · L · M · K · G · F · A · B · O · W · D · Neutron star · Black hole
Stellar Luminosity Classes
0 · I · II · III · IV · V · VI · VII