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Vermilion Parish Schools
Activity 9:  Hertzsprung-Russell Diagram (SI GLEs: 12, 13, 19; ESS GLEs:  36, 37)

Materials List: HR Diagram BLM, HR Star Data BLM, computer (1 for each student or student group), Internet access, computer projector (optional), HR Diagram Simulation BLM

So much has been learned about the stars over the years that it became necessary to organize this information into a diagram that could easily be interpreted. The Hertzsprung-Russell Diagram classifies stars by various characteristics and makes comparing them relatively simple.

Part A: Students will create a data table using star data of nearby and/or bright stars found on the HR Star Data BLM. Next, they will create a scatter-plot graph on the HR Diagram BLM; the graph should be labeled “brightness” on the y-axis and “temperature” on the x-axis. This is a model of the HR Diagram; to check students’ graphs, use any HR diagram, which can be found in most textbooks. Students determine the correct placement of their star on the graph. (Four groups of stars should be formed. Students can use an open circle “o” to represent white and outline a yellow circle for yellow-white colored stars.)  Allow time for students to individually examine the data and look for any inferences and observations that they can make from the data. Then ask students, What do the groups have in common? How are they different? Where are the oldest stars? How is the color of the star related to its temperature and its age? What is the order of star colors in the main sequence? Why are supergiant, giant, and white dwarf stars not found in the main sequence? How does the life cycle of a star relate to where certain stars are found on the H.R. Diagram? Massive stars, such as the supergiants, eventually become neutron stars or possibly black holes and low mass stars reside in the main sequence and typically go through the order of colors. Students should understand that not all stars start their life cycles at blue. Some may start their life cycle as white, yellow, orange, or red. How does the Sun compare to other main sequence stars? Have students research what the letters of the mnemonic OBAFGKM (Spectral class) represent, and submit a written paragraph on their meaning.

Part B: Students will observe the evolution of a star, which is largely determined by its initial mass. The computer simulation shows large stars burn their fuel fast and have short lives; similarly, small stars burn fuel slowly and last a long time. The Main Sequence is the expected relationship between temperature and luminosity (brightness). Students will be able to relate the initial mass of a star to its developmental stages and ultimate fate, especially as these relate to the Sun. To explore more about the evolution of stars, go to the HR Diagram Simulator at http://www.astro.ubc.ca/%7Escharein/a311/Sim/hr/HRdiagram.html. First, click the button labeled "100" one time to add one hundred stars to your diagram. The linear grouping that you see is called the Main Sequence. For the second set of questions, click on an individual blue star and write down its mass and main-sequence lifetime. To start the simulation, click on the button labeled "Evolve." Start the simulation again, but this time, click on an individual star and observe its luminosity as the simulation progresses.

Distribute the HR Diagram Simulation BLM to students. They can work independently on computers with Internet access in small groups of two, or this part of the activity can be completed as a whole class with a computer and projector.  There is a HR Diagram Simulation Key for the teacher’s use.




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