Astronomy Laboratory 11 – The H-R Diagram

Module Introduction

A plot of luminosity (absolute magnitude) against the colour of the stars ranging from the high-temperature blue-white stars on the left side of the diagram to the low temperature red stars on the right side. This diagram below is a plot of 22000 stars from the Hipparcos Catalogue together with 1000 low-luminosity stars (red and white dwarfs) from the Gliese Catalogue of Nearby Stars. The ordinary hydrogen-burning dwarf stars like the Sun are found in a band running from top-left to bottom-right called the Main Sequence. Giant stars form their own clump on the upper-right side of the diagram. Above them lie the much rarer bright giants and supergiants. At the lower-left is the band of white dwarfs - these are the dead cores of old stars which have no internal energy source and over billions of years slowly cool down towards the bottom-right of the diagram.
Hertzsprung-Russell diagram, or H-R diagram. Some 22,000 stars make up the data for this specific illustration. HRDiagram by Richard Powell is licensed under CC BY-SA 2.5

The Hertzsprung-Russell Diagram, H-R Diagram, is a useful tool which plots stellar luminosity versus temperature. Building on the Star Colors and Spectroscopy lab, you will detail how the H-R Diagram works, and plot some of the stars observed in Lab 10, Star Colors and Spectroscopy. (1)


At the end of this module, students will be able to:

  • Plot a H-R diagram using provided data
  • Analyze the data and make interpretations using the H-R diagram (1)


The material in this module includes content designed to meet the following course outcomes:

  • Explain and apply major concepts in astronomy including planets, satellites, stars, meteors, galaxies, and theories of the universe.
  • Demonstrate knowledge of scientific method.
  • Communicate scientific ideas through oral or written assignments.
  • Interpret scientific models such as formulas, graphs, tables and schematics, draw inferences from them and recognize their limitations.
  • Demonstrate the ability to think critically.
  • Demonstrate the ability to use scientific and quantitative reasoning. (1)

Assigned Readings

Learning Unit 11


  • Plotting a H-R Diagram Exercise
  • Lab 11 Quiz (1)