DATE: ________________ ___________________________
PERIOD: __________
Do you think that taller students tend to weigh more or less than shorter students? You could examine this by plotting the students in your class on a graph, with height on one axis and weight on the other. Each student would be plotted as a point on the graph. What do you think that graph would look like?
In general, shorter people tend to weigh less and taller people tend to weigh more. So, your graph would probably show a pattern, rising from the lower left corner (shorter, lighter people) toward the upper right corner (taller, heavier people).
In the early 1900s, two astronomers, Eljinar Hertzsprung, from Denmark, and Henry Norris Russell, an American, made a similar plot using data they had for nearby stars. They didn't know what, if anything, their plot would reveal. What they found was a way to classify stars that is still widely used in the science of astrophysics. Plots like the ones they created are still called Hertzsprung-Russell diagrams.
Classifying Stars Based on a Single Attribute
In this activity, you will classify stars based on a single attribute.
1. In the Gizmotm, under Star collection, be sure that Arrange stars is selected. In the dropdown menu at the top of the screen, set Arranged by to Color. Drag eight stars of a variety of colors stars from the Star collection into the region above the color scale. Position the stars where you think they fit on the color scale shown.
1. How does the color of the star seem to relate to the size (radius) of the star, if at all?
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2. When you have eight stars positioned above the color scale, press Sort stars to place them exactly on the color scale. Did they move much from where you had placed them?
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3. Click on Move all to move all of the stars onto the field. Then click Sort stars. Are the stars smoothly spread across the entire range or do they appear at distinct positions?
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2. Click Reset. Under Arranged by, select Temperature. Drag eight stars to the temperature scale in the large black area. Note that when you mouseover any star, you can see the star's name, temperature, luminosity (brightness), radius, and mass in the upper right corner. Place eight stars of various colors and sizes along the temperature scale. (Note that the space between 1000�C and 2000�C is the same size as the space between 10000�C and 20000�C. This type of scale is a logarithmic scale.)
1. Does the temperature of a star have any relation to its size? Justify your answer based on the distribution of stars along the temperature scale.
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2. Does the temperature of a star have any relation to its color? Justify your answer.
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3. Click on Move all, and then click Sort stars. What connection do you see between temperature and color of a star?
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3. Click Reset. Repeat the same process as above for Luminosity, Radius, and Mass. (Remember to click Sort stars each time you pick a new trait.) Click on Move all, and then click Sort stars to answer the next few questions.
1. Does a star's luminosity appear to be related to its size? Explain.
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2. Does the star�s luminosity appear to be related to its color. Justify your answer.
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3. What relationships do you see involving the radius of stars? Explain.
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4. What relationships do you see involving the mass of stars? Explain.
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Classifying Stars Based on Two Attributes
In this activity, you will classify stars based on two attributes.
1. Click Reset. Select Graphical plot. Using the dropdown menus at the top of the screen, select Temperature vs. Color. Drag eight stars from the Star collection onto the plot, positioning them based on their color and temperature.
1. Based on your plot, does the temperature of a star relate to its color?
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Why or why not?
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2. Click Move all, and then click Sort stars. Describe the shape of the graph.
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3. What relationship do you see between the temperature and color of stars?
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4. Explain. Does this agree with your finding from the first activity?
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2. Repeat the process for Temperature vs. Mass. (Remember to click Sort stars.)
1. Is there a relationship between the mass of a star and its temperature?
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2. If so, what is that relationship?
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3. Does the plot have the shape of a perfect line, or is it a scatter with a trend?
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What does that tell you about the relationship between temperature and mass?
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The Hertzsprung-Russell Diagram
The Hertzsprung-Russell diagram is a two-dimensional graph relating luminosity to temperature. One unusual characteristic of the H-R diagram, as it is known, is that the temperature scale on the horizontal axis is "backwards" from normal.
1. Click Reset. Select H-R diagram. Drag ten stars from the Star collection onto the plot. Position them based on their luminosity and temperature. Remember, the Gizmo displays both when you mouseover a star.
1. Based on the stars that you've placed on the H-R diagram, do you perceive any relationship between luminosity and temperature? If so, describe that relationship.
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2. Click Move all and then click Sort stars. Describe any relationship you can see now between luminosity and temperature of stars. (It may help to drag some of the stars slightly out of position so that you can recognize where several stars are overlaying one another.)
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2. Check Show star groups. Four major star classifications based on the H-R diagram are shown. The huge majority of stars fall along what is called the main sequence.
1. How does the star at the lower right end of the main sequence compare to the star at the upper left end of the main sequence? Discuss temperature, luminosity, and mass. (Again, be sure to mouseover the stars to see their masses.)
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It is now known that, in general, the least massive main sequence stars are at the lower right end of the sequence and the most massive are at the upper left end of the sequence.
2. State the above relationship in your own words. Discuss how mass relates to temperature and luminosity for main sequence stars.
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3. Describe the Giants and Supergiants. How are their radii different from main sequence stars?
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How are their temperatures different?
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You might notice that there are relatively few giants and supergiants. It is now known that these are stars in the latest phases of their life cycles. Earlier in their life cycles, they were part of the main sequence. How do the White dwarfs compare with stars in the main sequence? Discuss radius and temperature.
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