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Spectral Types
 Teacher's Guide
     - Goals
     - Background
     - Structure
     - Questions
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 To Student Project

Spectral Types

This project teaches students about the types of stars. They will learn that astronomers use a system based on the stars' spectra, and that this system is actually a temperature scale for the stars. They will also learn what causes the absorption and emission lines in a star's spectrum, and why stars of different temperatures have different lines. They also will have a brief look at stars that do not fit into the traditional spectral types.

For more information on spectral types of stars, read the About Astronomy: Stars section of SkyServer, or look up one of the following references:

Kaler, James, Stars and Their Spectra, 1997

Spectra, a web page by James Kaler

Project Goals

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

  • Understand that each star has a unique spectrum - a series of absorption and emission lines
  • Explain that stellar absorption lines are caused by gas in the outer layers of a star's atmosphere absorbing photons from the star
  • Know that the pattern of absorption lines depends on the temperature of the star
  • Classify the spectrum of a star from its absorption lines
  • Identify which types of stars are most common, and understand that some types of stars are too faint observe, even with large telescopes

Background Knowledge

Students should have a basic understanding of the nature of light before undertaking this project. They should know that light is a wave, and that different wavelengths correspond to different colors. Students also need to be able of read and understand graphs of spectra.

No mathematics knowledge is necessary for the Spectral types project.

Project Structure

The first section lets students classify stars based on their spectra. The students should start learning to look for patterns in spectra during this section. After developing their own classification system for stars, they will discuss their system with another group and try to strengthen the system. It is a good idea to set a firm time limit, or students may spend a long time debating their classification systems.
Estimated time: 30 - 40 minutes

Students then learn that the spectrum of a star is like its fingerprint. They see how gas in the star's atmosphere absorbs, and sometimes emits, light at certain wavelength, giving each star its distinctive spectrum.

Then, the students learn that different elements show spectral lines at different temperatures. They will learn how to use these lines to classify stars, and to estimate the stars' temperatures.
Estimated time: 20 minutes

Students will have an opportunity to practice classifying stars. Finally, they will compile all their data in an attempt to find out what types of stars are most common and what types of stars are least common.
Estimated time: 45 minutes

The last Exercises, Exercises 8-10, are the research challenges for this project. These exercises should not be done in the classroom for credit. They are designed to be completely open-ended, and to take many hours to complete. You may wish to give extra credit for completing any of the exercises. When students finish any of these exercises on their own, encourage them to E-mail their results to us. We will look over all the projects we receive, and we will put the best of them up on the project web site.

Questions and Exercises

Questions are designed to get students thinking about the way scientists work. Exercises are designed to get students to explore using SkyServer data to solve problems. For answers to all questions and 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.