Colors of Stars Teacher Notes


This project shows students the brilliant colors of stars, then teaches them why stars come in so many colors. Answering this question takes them through the definition of color in astronomy, the nature of the thermal radiation given off by hot objects, and the use of colored telescope filters.

For more information on how astronomers use color, and on the physical meaning of color, read the About Astronomy: Stars section of SkyServer, or look in any astronomy or physics textbook. Here are a few possible references:

Halliday, David, Jearl Walker, and Robert Resnick, Fundamentals of Physics, John Wiley and Sons, 2000

Hartmann, William K., Astronomy: the Cosmic Journey, Wadsworth, 1989

Kaler, James, Extreme Stars, Cambridge University Press, 2001

Project Goals

By the end of the project, students should be able to:

  • Recognize the rich variety of colors in the night sky
  • Ask scientific questions about everyday phenomena
  • Know that light is a wave, and explain the relationship between wavelength and observed color
  • Know the order of the visible spectrum, from red to violet, and the total electromagnetic spectrum, from radio waves to gamma rays
  • Explain how telescope filters are used in astronomy
  • Explain how the color of stars stars is related to the peak wavelength of light they emit
  • Explain why red, orange, yellow, and blue stars are common, while stars with other colors from the visible spectrum are rare
  • Look up data using several interfaces
  • Compare the astronomical definition of color to the color they see with their eyes
  • Understand that hot objects give off more thermal radiation than cool objects
  • Explain how the peak wavelength of thermal radiation changes as objects heat up
  • Explain why the color of a star can not be found from its temperature alone
  • Find peak wavelengths of observed stellar spectra
  • Qualitatively understand how to find astronomical colors from a thermal radiation curve
  • Make simple x-y graphs
  • Identify cool and hot stars on different color-color diagrams
  • Use data to judge when a scientific analysis is appropriate
  • Prepare, execute, and interpret an independent scientific research project

Background Knowledge

Before beginning this project, students should:

  • know that stars come in different colors
  • know that light is composed of waves with definite wavelengths
  • know what stars, galaxies, and the universe are
  • know that hot objects glow, and that heat and light are related
  • have some experience with scientific reasoning
  • have mathematics experience up to and including Algebra I
  • know how to look up information using a web-based interface such as a search engine
  • have some familiarity with a spreadsheet program such as Microsoft Excel

Project Structure

The Color project is a long-term project, designed to take about 11 hours to complete. You may wish to assign some parts as homework. The project can be divided into four chapters:

Chapter 1: Introduction and Exploration – 1 hour

Chapter 2: Definition of Color in Astronomy – 2 hours

Chapter 3: Thermal Radiation, Temperature, and Observed Spectra – 3 hours

Chapter 4: Color-Color Diagrams – 4 hours

Chapter 5: Conclusion/Research Challenge – 1 hour

The Research Challenge, on the Conclusion page, should not be done in the classroom for credit. It is designed to be a completely open-ended and independent scientific investigation, and it should take many hours to complete. You may wish to give extra credit for completing it. Invite students to discuss their research questions and approaches with you.

Questions and Exercises

Questions are designed to get students thinking about the reasoning scientists use in their work. Exercises come in two types: Practice and Explore. Practice exercises let students practice using the concepts introduced in the project. Explore exercises are designed to get students to explore SkyServer data to discover concepts on their own. For answers to all Questions and Practice exercises, and sample responses to all Explore exercises, click here. To see the answers, you must have the Adobe Acrobat PDF viewer installed on your computer. Acrobat is available for free download at Adobe’s web site.

Students should be evaluated based on their written answers to the questions and exercises. You may use our sample scoring rubric or develop your own. If you use our scoring rubric, print out a copy for each student and attach it when you return his or her work.

For specific information on any part of the project, click Next