Classifying Stars

(a 6-8 Astronomy lesson plan)

From the unit: What would happen if the sun stopped shining?

Display printer-friendly version

Students will use what they learned in the previous lesson about the life cycle of stars to begin to classify stars. They will use a common scientific chart, the Hertzsprung-Russell Diagram, to place stars in different categories. Using this chart will help students distinguish between temperature and brighness of stars.
Standards and Benchmarks
AAAS Benchmarks
  • The sun is a medium-sized star located near the edge of a disk-shaped galaxy of stars, part of which can be seen as a glowing band of light that spans the sky on a very clear night. The universe contains many billions of galaxies, and each galaxy contains many billions of stars. To the naked eye, even the closest of these galaxies is no more than a dim, fuzzy spot.
  • Nine planets of very different size, composition, and surface features move around the sun in nearly circular orbits. Some planets have a great variety of moons and even flat rings of rock and ice particles orbiting around them. Some of these planets and moons show evidence of geologic activity. The earth is orbited by one moon, many artificial satellites, and debris.
  • Large numbers of chunks of rock orbit the sun. Some of those that the earth meets in its yearly orbit around the sun glow and disintegrate from friction as they plunge through the atmosphere -- and sometimes impact the ground. Other chunks of rocks mixed with ice have long, off-center orbits that carry them close to the sun, where the sun's radiation (of light and particles) boils off frozen material from their surfaces and pushes it into a long, illuminated tail.
  • Students generate questions (about star formation and life cycles) based on observation and prior knowledge.
  • Students use appropriate tools and techniques to gather, analyze and interpret data.
  • Students describe and explain orally to the whole class common observations of the day and night skies (specifically, specific characteristic of stars on H-R Diagram).
Class Time Needed
One 50 minute class period
Teacher Preparation
More information about the H-R diagram
Student Materials
  • Colored pencils (Red, blue, yellow, black, white, brown)
  • Lab notebook
  • Notes from Life Cycle of Stars (in notebook) (Label only the star names not the axes)
  • Textbook
Teacher Materials
  • Transparency of HR Diagram (using the URL or another source you find)
  • Labels for classroom for HR Diag. game
  • Copies of HR Diagram (from URL) to use for worksheets if desired
Science Background

H-R Diagram
Scientists have been gathering data on different types of stars for many years. One of the most helpful summaries of this data is the Hertzsprung-Russell Diagram. In the 1910s, two astronomers named Ejnar Hertzsprung and Henry Russell studied properties of stars. Using powerful telescopes, they measured the temperature of stars by studying the color of a star.

To help them keep track of each star, they made a diagram of temperature and brightness. The diagram looked like a graph. It had temperature along the bottom. Hot was to the left, and cool was to the right. It had brightness/magnitude along the side. Very bright was at the top, and very dim was at the bottom.

Hertzsprung and Russell did not know each other at this time. In fact, Hertzsprung lived and worked in Germany, while Russell lived and worked in the United States. Both wrote articles about their research, and it was only after they both saw each other's articles that they became friends and worked together.

This diagram was very important, because it was based on scientific data. It helped astronomers develop theories to explain how stars behave. It was a snapshot of a moment in astronomical time. Hertzsprung and Russell used the diagram to try to explain how stars are born, live, and finally die.

The first group of stars is called the main sequence stars. These stars behave as everyone expects them to. If they are hot, they are bright. If they are cool, they are dim. All of the main sequence stars are along a line that goes from the bottom right to the top left of the diagram.
The second group of stars is called the red giants. They sit in the top right corner of the diagram. These stars are very cool, and at the same time very bright.
The third group sits in the bottom left corner of the H-R Diagram. They are the white dwarfs. They are very hot, but quite dim. This is because they are very small, perhaps smaller than the Earth.
When looking at the H-R Diagram, note that star color corresponds directly to star temperature, not brightness. This means that a red star could be large or small, but is quite cool either way. Similarly, a blue star could be large or small, but is always hot.

Learning Activities:

1. Begin lesson with question: How do the size and distance of a star affect how bright it looks to us? (This question has already been addressed in the previous lesson. It is just a warm up question to get students thinking.) Ask students to volunteer information from presentation (the previous lesson) including star types and characteristics i.e. color, size, brightness, temperature, and color. Make sure to review star color and temperature relationship. Write the characteristics on the board. (5 min.)
This lesson builds heavily on what students learned in the previous lesson, so take some time today to help students remember what they've learned about different types of stars and their colors and temperatures. You might consider making a table to organize the discussion if your students need more structure.

2. Explain that astronomers who studied the stars in the 1800's found so many stars that it was hard to organize information about them into useful patterns. Many astronomers worked on ways to classify stars. Some were American astronomers, like Edward Pickering, Antonia Maury and Annie Jump Cannon. Some of their early work led to diagram we now use.
Annie Jump Cannon is a very famous and important scientist. You might encourage students to learn more about her life and contribution to the field of astronomy. It is very important to highlight women and minority scientists who made significant contributions to topics the class is studying.
Then tell students about two astronomers named Hertzsprung (form Germany) and Russell (from England). They needed a way to record and keep track of each star, and so they created this table. (Give students copies of worksheet with labeled stars but without labels on the axis.) Then ask students to see if they can figure out how the stars were classified by Hertzsprung and Russell in groups of four using characteristics on board. Students should work in small groups to figure out characteristics of each star and draw conclusions. They should be able to determine temperature in terms of hot or cool and brightness in terms of bright or dim and how these fall on the axes of the table. (10 min.)
[?] Why should students collect evidence to answer questions?
[?] How can I help my students collect evidence?

3. Student Group Discussion (15 min.)
Go over what students found and make sure students have an understanding that one axis should be labeled temperature and one axis should be labeled brightness/magnitude. Make connection to original HR Diagram. (using overhead)

4. Playing the HR Game to understand the Diagram (20 min.)
  • Put magnitude-Bright and Dim and Temperature-Hot and Cool labels in the room to enact HR Diagram.
  • Have students work in their groups of 4 and decide which type of star they would like to be. (There are eight choices: Red Giant, Blue Giant, Red Supergiant, Main Sequence, White Dwarfs, Brown Dwarfs, Red Dwarfs, and Black Dwarfs.)
  • Explain the rule for the game. Students will have to stand in the room, as if they were a star on the diagram. (The classroom itself is a HR Diagram). No two groups should pick the same stars. Remember to give students time to think if their stars are being taken. This will get students to think about characteristics of the other stars and also makes sure students are paying attention to the other groups' presentations.
  • Ask students not to tell anyone else or tell other groups their choice. Give them a few minutes to discuss the characteristics of star. Have each group, one at a time, stand in the location that their star would be located on the diagram according to their characteristics.
  • Have the class explain their stars' characteristics and do a tally vote to see what the class thinks each groups star is. Have the presenting group give the answer and why they are the star they chose.
  • If group is wrong, allow students or rest of the class to help explain what star they really are.
  • Allow students time between each presentation to think of another star's characteristics if their stars has been presented. Groups will present until all 8 stars are covered. (Black Dwarf will stand in the hall) Put up finished transparency/worksheet that they were working on and make sure they have labeled everything correctly.
5. Pass out homework assignment. Writing Prompts:
  • After learning about the HR Diagram, how do astronomers classify stars?
  • Is this diagram a good way to classify stars? Explain why or why not.
  • Can you think of other information scientists might want to know about stars?
[?] Why should students communicate and justify their findings?
[?] How can I help my students communicate and justify their findings?
Students are being assessed while working in their groups by contributing information and their placement on the diagram. Also, the whole group discussion is part of the informal assessment.

They can also be assessed individually through their journal entries. Look to see what students have learned from the lesson in their journal entry. Also, check to see if they have gained a deeper understanding by asking them to evaluate the diagram. Consider spending part of the next class talking about their ideas from their journals.
Images of Inquiry
Click here to find out how you can customize this lesson.

This lesson focuses on Explanations & Evidence. (more)

How Jenny taught this lesson
After reading through the lesson, Jenny knows that talking about the H-R table as a scientific tool is important, but she's not sure how to do this and cover the content of the lesson as well. During her planning period, she visits the 8th grade science teacher and asks his advice. He tells her that he would have students draw analogies to the tools they use in their everyday lives to the tools used in the scientific community. Jenny likes that idea so she decides to get students to think of tools they use that help them organize information. She just spends 10 minutes on this in most of her classes, but one class really becomes interested, and before she knows it, 20 minutes have gone by. She makes sure to focus students on the idea that scientists need to find ways to organize their data (and she reminds them of the data tables they designed during their water quality units). She is glad she took the time for this discussion and will try to remember to remind students of it whenever they use new scientific tools in the future.

Author(s): Stephanie Coleman, Joyce Lin, Natalie Tunnell
Modified By: CASES Team

Questions about CASES?
}*{ Report a Bug