The Hertzsprung–Russell Diagram
Lesson notes
Overview
Plotting luminosity against temperature reveals the main sequence, giants and white dwarfs. This topic is rated intermediate and is number 35 of 98 in Earth & Space. Builds on the basics with relationships, methods and trade-offs.
What you are seeing
The panel above shows a model of an Earth or space system that you can adjust. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.
In depth
The HR diagram plots stars’ luminosity against surface temperature (with hot stars at the left). Most stars lie on a diagonal band called the main sequence, where they fuse hydrogen, with luminosity rising steeply with mass, L ∝ M^3.5. Red giants and supergiants sit above it, and white dwarfs below. The position of a star shows its stage of evolution, and the diagram of a cluster can be used to find its age.
Reading the relationship
The expression "L ∝ M^3.5" is a compact summary of the idea. It uses the symbols L, M; name what each one stands for before you start. Notice that it contains a proportionality, so the two sides rise and fall together. Then use the sliders to see how changing one quantity changes the others.
A guided exploration
1. Run the animation once with the default settings and describe in words what happens. 2. Change one slider at a time and note which quantity responds most. 3. Push each slider to its extreme and decide whether the result still makes sense.
Try this
Predict the outcome first, then test extreme slider values to find where the pattern changes or breaks.
Common pitfalls
Earth and space systems work on very different scales of time and distance. Check which scale a number refers to before comparing it with another.
How it connects
It builds on “The Life Cycle of Stars”, the topic before it in Earth & Space. Once you are comfortable, continue with “Stellar Lifetimes”.
Why it matters
Earth and space science helps us understand our planet, its climate and the wider universe.
Where you might use it
- Revising “The Hertzsprung–Russell Diagram” before a class, exam or certification
- Forecasting weather and understanding climate records and their uncertainty
- Planning for earthquakes, floods and other natural hazards in cities
- Interpreting satellite images, space missions and the age of rocks and stars
Frequently asked questions
What is The Hertzsprung–Russell Diagram?
Plotting luminosity against temperature reveals the main sequence, giants and white dwarfs. It is an intermediate topic in Earth & Space.
How do I use the The Hertzsprung–Russell Diagram simulation?
The panel at the top shows a model of an Earth or space system that you can adjust. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression L ∝ M^3.5 packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.
Who is this topic for?
Builds on the basics with relationships, methods and trade-offs. If the quiz feels hard, reread the lesson notes and try the previous topic first.
What should I learn before this?
Start with “The Life Cycle of Stars”, the previous topic in Earth & Space. Each topic in a subject builds on the ones before it.
How do I track my progress?
Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.
Quick quiz
More in Earth & Space
See all →Stellar Lifetimes
Massive stars burn fuel so fast that they live only millions of years.
Inverse-Square Law of Light
Starlight spreads over a sphere, so brightness falls with the square of distance.
Parallax and Stellar Distance
Nearby stars shift against the background as Earth orbits; the angle gives distance.