⭐ H–R Diagram

📖 The Physics

The Hertzsprung–Russell diagram is astronomy's master chart: it plots stars by surface temperature (hot on the left) against luminosity (true brightness).

Most stars, including the Sun, lie on a diagonal band called the main sequence. A cool but very bright star must be enormous — a giant; a hot but faint one must be tiny — a white dwarf.

Keep the temperature Sun-like but grow the radius and your star climbs into the giant region. Make it hot and tiny and it drops down to the white-dwarf corner. This diagram maps out the whole life story of stars.