What quantities are plotted on a Hertzsprung–Russell diagram?

Stellar luminosity (or absolute magnitude) is plotted against surface temperature (or spectral class).

In which direction does temperature increase on an HR diagram?

Temperature increases from right to left along the horizontal axis.

Describe the position and characteristics of the main sequence on an HR diagram.

The main sequence is a diagonal band running from top-left (hot, luminous) to bottom-right (cool, dim) where stars spend most of their lives fusing hydrogen.

Where do red giants appear on an HR diagram and why?

Red giants appear in the upper-right region: they have high luminosity but relatively low surface temperature.

Where are red supergiants located on an HR diagram compared to red giants?

Red supergiants appear at the top-right of the HR diagram with even higher luminosity than red giants.

OCR A-Level Physics A H556

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The Hertzsprung-Russell diagram

1 thing to know
Papers 1, 2 and 3

Overview

Recall questions on the axes of the Hertzsprung-Russell diagram, the positions of main sequence stars, red giants, red supergiants and white dwarfs, and how a low-mass star moves across the diagram as it evolves.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

In which direction does luminosity increase on an HR diagram?

Questions from this subtopic

Each one with the model answer underneath.

1
What quantities are plotted on a Hertzsprung–Russell diagram?
Model answer
Stellar luminosity (or absolute magnitude) is plotted against surface temperature (or spectral class).
2
In which direction does temperature increase on an HR diagram?
Model answer
Temperature increases from right to left along the horizontal axis.
3
In which direction does luminosity increase on an HR diagram?
Model answer
Luminosity increases upward along the vertical axis.
4
Describe the position and characteristics of the main sequence on an HR diagram.
Model answer
The main sequence is a diagonal band running from top-left (hot, luminous) to bottom-right (cool, dim) where stars spend most of their lives fusing hydrogen.
5
Where do red giants appear on an HR diagram and why?
Model answer
Red giants appear in the upper-right region: they have high luminosity but relatively low surface temperature.
6
Where are red supergiants located on an HR diagram compared to red giants?
Model answer
Red supergiants appear at the top-right of the HR diagram with even higher luminosity than red giants.

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