The Hertzsprung-Russell Diagram

Classifying Stars & Tracing Stellar Evolution

Arguably, the most important diagram in astronomy, the Hertzsprung-Russell Diagram (HRD), shows how plotting the brightness of stars against their surface temperature enables the classification into different stellar types and maps their life cycles.

Learn how astronomers measure the true brightness or luminosity of stars and their surface temperature, followed by how this is used to construct an HRD and interpret the information provided, including what’s going on inside stars at each stage of their lifespan to cause them to expand and change colour.