As you learned in the last section, not all stars are the same nor are they in the same stage in their life cycle.

In 1911, Ejnar Hertzsprung, a Danish astronomer, used a graph to compare the temperature and brightness of stars. Two years later, Henry Norris Russell, an American astronomer, made similar graphs using slightly different data. The combination of their ideas is now called the Hertzsprung-Russell diagram (or H-R diagram). The Hertzsprung-Russell diagram (or H-R diagram) is a graph that shows the relationship between a star’s surface temperature and brightness. (Brightness is displayed as absolute magnitude or luminosity.)

portraits of Hertzsprung and Russell

Source: Hertzsprung and Russell, Museum of Flight

The H-R diagram is also a tool for studying the nature of stars and how they change over time.  Below is an example of an H-R diagram.

Source: H-R Diagram, Aspire

How do you read the H-R Diagram?


ASPIRE Astrophysics Science Project


Let’s see how well you can read the H-R diagram. Use the link to access the interactive.

How does a star change through its life time? (In the animation, a star will move through the diagram. Note: in real life a star does not physically move around as it ages.) The animation shows you how its brightness and surface temperature changes over time.