The Hertzsprung–Russell Diagram: Mapping Stellar Life

The Hertzsprung–Russell diagram is a cosmic map showing how stars change over their lifetimes.
It plots stars by brightness (luminosity) against their surface temperature or color.
Most stars—including our Sun—fall along the “main sequence,” where hydrogen fusion powers them.
Blue stars sit at the hot, bright corner; red dwarfs at the cool, dim end.
The diagram reveals stellar evolution: from newborn protostars to red giants and white dwarfs.
Supergiants like Betelgeuse shine at the top, towering over the Sun in size and brilliance.
White dwarfs cluster at the lower left—tiny, faint stellar remnants cooling over time.
Astronomers use the H–R diagram to estimate a star’s age, mass, and future.
The H–R diagram was independently developed in the early 1900s by Ejnar Hertzsprung and Henry Norris Russell.
It remains one of astronomy’s most powerful tools for unlocking stellar secrets.