---
title: "The Hertzsprung-Russell Diagram and Stellar Evolution"
description: "Plotting luminosity against surface temperature sorts stars into a main sequence, giants and white dwarfs, and a star's track across the diagram is its life story. Position on the main sequence is set"
canonical: https://lightmysky.com/learn/science/the-hertzsprung-russell-diagram-and-stellar-evolution-mt_zMZDIB5TGc
source: https://lightmysky.com/learn/science/the-hertzsprung-russell-diagram-and-stellar-evolution-mt_zMZDIB5TGc.md
retrieved: 2026-09-12
---

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# The Hertzsprung-Russell Diagram and Stellar Evolution

Plotting luminosity against surface temperature sorts stars into a main sequence, giants and white dwarfs, and a star's track across the diagram is its life story. Position on the main sequence is set almost entirely by mass.

Subject: Science · Area: Astronomy & Astrophysics · Ages 21 to 22
Page: https://lightmysky.com/learn/science/the-hertzsprung-russell-diagram-and-stellar-evolution-mt_zMZDIB5TGc

## Ready when they can

- Places a star on the diagram from its temperature and luminosity
- Explains why main sequence lifetime falls sharply as mass rises
- Reads the age of a cluster from where its main sequence turns off

## Lesson: Reading the life story of stars

The Hertzsprung-Russell diagram plots each star by surface temperature against luminosity. Temperature runs backward, hottest on the left. Most stars fall on the diagonal main sequence band, with hot bright giants above and faint compact white dwarfs below.

**Example.** Place a star with two readings: its spectral class gives the temperature, and its apparent brightness plus distance gives the luminosity. Drop that point onto the diagram and you know at once whether it is a main sequence star, a giant, or a white dwarf.

A star spends most of its life fusing core hydrogen on the main sequence, and its mass fixes how long that lasts. Heavy stars burn fiercely to support their weight, so a star ten times the mass of the Sun lives far shorter. Mass sets position and pace together.

**Tip.** A cluster gives every star the same birthday and composition, so mass is the only difference. Massive members leave the main sequence first, and the point where the sequence bends away is the turnoff. Read the turnoff mass and you read the cluster age.

**Recap.** Plot temperature against luminosity, let mass set the pace, and read cluster ages from the turnoff.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Energy Transport and Nuclear Burning in Stars](https://lightmysky.com/learn/science/energy-transport-and-nuclear-burning-in-stars-mt_2rc4UAMyl-)
- [Energy Levels and Line Spectra](https://lightmysky.com/learn/science/energy-levels-and-line-spectra-mt_RlMCSDxE5q)