Hertzsprung-Russell (H-R) Diagram
A foundational scatter plot of stellar luminosity versus surface temperature (or spectral type) used to trace stellar evolution phases.
Governing formula
L ∝ R² T^4 (Plot of Absolute Magnitude vs Spectral Type)
SI unit
Luminosity (L_☉) vs Surface Temp (K)
In depth
Created by Ejnar Hertzsprung and Henry Norris Russell in 1910. Stars cluster into distinct regions: Main Sequence (~90%), Red Giants and Supergiants (top right), and White Dwarfs (bottom left).
Examples in the real world
Tracing a 1-solar-mass star's life path on the H-R diagram from Main Sequence to Red Giant branch to White Dwarf.