Download HR Diagrams

H-R Diagrams
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.
Part A: Star Colour Classification
1. In the Gizmo, under Star collection, be sure that
Arrange Stars is selected.
2. In the dropdown menu at the top of the screen, set
Arranged by to Color.
3. Drag six or eight stars of a variety of colors stars from
the Star collection into the region above the color scale.
4. Position the stars where you think they fit on the colour
scale shown.
5. Questions
a. What is the relationship between colour and
the star’s radius?
b. Press sort stars. Did your stars move from
where you positioned them?
c. Move all the stars on to the scale and then sort them by selecting the sort stars option. Are
the stars spaced equally across the scale or do they clump together in certain locations?
Part B: Temperature
1. Click Reset.
2. Under Arranged by, select Temperature.
3. Drag several 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.
4. Place six or 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.)
5. State the relationship between the following properties
of a star and justify your answer. Remember to click Sort Stars every time you pick a new trait.
a. Temperature and radius?
b. Temperature and colour?
c. Temperature and luminosity?
d. Temperature and mass?
Part C: Classifying Stars Based on Two Attributes
1. In click Reset.
2. Select Graphical plot.
3. Using the dropdown menus at the top of the
screen, select Temperature vs. Color.
4. Move all the stars onto the graph and then click
sort stars.
5. Questions
a. Based on your plot, does temperature of
a star relate to its color? Why or why
not?
b. What is the shape of the graph? What
type of relationship does this indicate?
Does this sense with what you found in
Part B?
6. Repeat this process for the relationship of Temperature vs. Mass.
a. Based on your plot, does temperature of a star relate to its mass? Why or why not?
b. What is the shape of the graph? What type of relationship does this indicate?
7. Repeat this process to determine the relationship exist between:
a. Luminosity and colour?
b. Radius and mass?
c. Mass and colour?
d. Luminosity and mass?
e. Luminosity and radius?
Part D: 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 eight or 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. 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.
2. Click Move all and then click sort stars. 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. 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. 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 stars are at the upper left end of the sequence. State the relationship in your
own words and discuss for mass relates to temperature and luminosity for the main sequence stars.
3. Describe the Giants, Supergiants, and white dwarfs. How are their radii different for the main
sequence stars? How are their temperatures different? How do their numbers compare to the
number of stars on the main sequence?