Name______________
Hertzsprung-Russell (HR) Diagram
Visit the following site:
http://aspire.cosmic-ray.org/labs/star_life/hr_diagram.html
HR Diagram
The Hertzsprung-Russell Diagram is a tool that shows relationships and differences between stars. The
diagram shows stars at different stages of its life cycle. It also shows the relationship between size and
brightness. The HR Diagram can be used to learn a number of things about a star. However, learning to
use the HR Diagram takes practice.
Let’s determine what the HR Diagram can tell us. (Each dot represents a star)
 Absolute magnitude (luminosity)
 Surface temperature
 The graph is opposite. Higher temps are to the left.
 Brighter as you move up
Look at the sizes on the diagram. What is the pattern for star size? Where are most of the stars?
 Brighter stars are bigger
 Most of the stars are on the MAIN SEQUENCE (draw on board and label)
Interactive lab
Scroll to the bottom portion of the page and click on the diagram. Take a minute or two and try to
determine the brightness and temperature of the stars.
Betelgeuse (a):
Alpha Centauri B (b):
Vega (d):
Sirius B (e):
Our Sun (c):
Why are most of the brighter stars bigger?
Analyzing Stars Using the HR Diagram
Click on the right arrow to take you to the next page. Then, click on the diagram to begin. The questions
below follow the questions on the tutorial. Write the answers to the questions.
Hypothesis background: assume that all stars are the same size (they are not all the same size).
Differences in brightness would then be due to surface temperature.
1. Which hypothesis would match this background information?
2. Where would you expect to find other main sequence stars of the same size on the diagram?
3. What is the relationship between surface temperature and size of a star?
4. Which hypothesis is true then?
5. Different stars have different masses.
6. Stars with a mass similar to 10 Msun will have almost all of the same characteristics as 10 Msun.
7. The most massive stars shine very dimly compared to smaller stars.
8. Is the majority of a star’s life cycle is spent as a main sequence star? Why or why not?
9. Will a star with a large mass will radiate more energy into space and appear brighter than a star with a
smaller mass? Why or why not?
10. Do stars with smaller masses have a greater luminosity (brightness) than larger mass stars? Why or
why not?
11. Some very bright stars do not have high surface temperatures. Some stars have high surface
temperatures but do not shine very bright. These stars are not on the main sequence. The differences in
luminosity are due to the mass or size of the star. Describe a real-life comparison (example) to a large,
cool star that is bright. Describe a real-life example of a small, hot star that is not very bright. Why are
the large, cool stars brighter than the small, hot star?
Review of star properties
What can astronomers measure by looking at star parallax?
How are absolute magnitude and apparent magnitude different?
How does mass affect absolute magnitude?
Will a very hot star appear blue or red?