Stars have different fundamental properties such as mass, color, temperature, size, brightness, fusion rate, energy output, and lifespan. Students typically first learn about these differences from Hertzsprung-Russell (H-R) Diagram, an historic plot used to visualize trends in stellar properties. In this investigation, students use color-magnitude diagrams, which are similar to H-R Diagrams, to analyze data from stars in star clusters. Students uncover patterns in star characteristics and compare those to the Sun’s properties. Students gain insights about how the initial stellar mass, nuclear fusion rate, and the balance of internal forces determine star properties, and how these properties change throughout the lifetimes of stars. Finally, students apply these concepts to analyze star clusters to determine their distance and age.

Prerequisite Concepts

• Students should know that nuclear fusion is the internal process that produces electromagnetic radiation in stars.
• Students should know that the changes stars undergo throughout their lifetimes are due to changes in nuclear fusion within the star.
• Students should have been introduced to the H-R Diagram, and how it illustrates the relationships between stellar properties and the evolution of stars.

Learning Outcomes

• Students use color-magnitude diagrams to compare temperature (color), luminosity, and size of main sequence stars.

• Students compare the properties of the Sun to other main sequence stars.

• Students explain how the initial mass of a main sequence star determines the rate of nuclear fusion and lifespan of a star.

• Students use isochrones to fit data to determine the distance and age of a star cluster.

Essential Questions

• What causes the differences in the observed properties of stars?
• How does the Sun compare to other stars?
• How do stars like the Sun change as they evolve?
• How can we determine the distance and ages of stars?