The Process

 

Part IV - Group: Life Cycle of a Star

 

Part IV is a group activity, during which you will begin to learn how to identify stars by their magnitude, color, and temperature, and spectral class. This should take one to two class periods.


What Types of Stars are in Our Universe?
Stars come in many different colors and sizes. We can determine a star's type by studying its color and brightness. Once we know a star's type, we can estimate its age, how long it lives, and the amount of energy it would provide to a nearby planet. This information is important to know when determining if a star could support life on an orbiting planet or moon.

What You Need to Do. As a group:
A. Examine the star circles your teacher gives you. Each circle has the following information.
• star name – the common or catalog name of the star
• temperature – the temperature of the surface of the star
• brightness – the number of times brighter the star is than our sun (a fraction means it is dimmer than our sun)
• expected lifetime –the number of years stars of this type are expected to exist at this color and brightness
B. Correctly position and attach your circles on the provided chart's temperature and brightness axes.  LEAVE OUR SUN UNTIL LAST.
C. Once all the star circles are in place, sketch the axes and distribution of the stars in your journal.

As a group, identify trends on the chart by discussing the following questions and type the answers neatly in to a document.  The main purpose is for you to analyze the chart and then to indentify trends/patterns in color, brightness and temperature.  Then to use these  trends/patterns to answer the questions.

  1. Describe the general trend between temperature and brightness; color and brightness; color and temperature.
  2. What is the color and brightness of the most abundant stars? The rarest stars?
  3. What are the characteristics of the stars that do not conform to the graph's trends? (i.e. outliers)
  4. In terms of the graph's trend, is our sun typical or an outlier?
  5. If you replaced the temperature scale on the graph's x-axis with a color scale, which color would be closest to the graph's origin and which would farthest away?  Label the spectral classes (O, B, A, F, G, K, M) appropriately under each star color in your diagram.
  6. In the stars that fit the general trend (these are often called main sequence stars), what relationship do you notice between color and expected lifetime?
  7. Why might stars of one color be more abundant than other star colors?
  8. Which type(s) of star should we consider first when looking for stars that might have life-supporting worlds around them? Why?
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