The Hertzsprung-Russell (HR) Diagram plots main sequence stars along a distinct diagonal band.

The HR Diagram is a fundamental tool in stellar astronomy, plotting stars based on their luminosity (or absolute magnitude) against their surface temperature (or spectral type). Main sequence stars fall along a narrow, diagonal band running from the upper-left (hot, luminous, massive blue stars) to the lower-right (cool, dim, less massive red stars). This distinct placement reflects the relationship between a star's mass, temperature, and luminosity while it is fusing hydrogen in its core, providing a powerful visual representation of stellar evolution.