Hertzsprung-Russell diagram showing stars in the main sequence.
The main sequence is a region on a Hertzsprung-Russell Diagram where most stars appear. Any star that is plotted in that area is a main-sequence star. The Sun is a main-sequence star. Most of the stars in the Milky Waygalaxy and most other galaxies are also main-sequence stars. This is because stars on the main sequence are highly stable, so they remain there a long time.