PART I: HERTZSPRUNG-RUSSELL DIAGRAM OF STAR CLUSTERS
Star clusters are groups of stars that formed at approximately the
same time from the same large collapsing nebula and therefore are a
similar distances from our solar system; they share a common history.
Some clusters, called open clusters, are made up of only a few
hundred stars. They are held together by their mutual gravity and
move together through space.
The Pleiades are an open star cluster, one of the closest to Earth, and
visible to the naked eye. The M44, or Beehive star cluster is another
open cluster, close enough to Earth that it was observed by Galileo.
1.Find Pleiades in Stellarium. Zoom in until you are able to see its
2.Click on each star. Its information will be shown to the top left of
3.Use the information to finish an H-R diagram (Figure 1) as well as
4.In the H-R diagram, use the ID (number) of each star to label it.
5.Answer the questions for Pleiades.
6.Now repeat Step 1 and 2 for M44.
7.Add stars of M44 to Figure 1 (use their letter IDs to label), and finish
8.Answer the questions for M44.
9.Write a summary.
Note: some columns of Table 1 and 2 cannot be read directly from
Stellarium — they have to be inferred from the H-R diagram (so don’t
ask me why there is no information of temperature in Stellarium).
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Table 1: Pleiades
Earth in ly
Table 2: M44
Distance from Earth
A. 39 Cancri
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Questions for Pleiades:
1. Which information in Table 1 could you get from the H-R Diagram.
2. Which star is the brightest as viewed from Earth? Which star is the faintest?
Which stars have the greatest and least luminosity?
3. Since the size of each star also tracks diagonally across the H-R diagram from
the smallest objects in the lower left to the largest objects in the upper right,
which star has the largest radius? Which star has the smallest radius?
4. What can you say about the spread of distance among the stars in this cluster
compared to the distance of this cluster from our solar system?
5. Which, if any, stars are located off the main sequence? What does that say
about the age of this cluster?
6. Since all of these stars formed at about the same time and from the same
collapsing nebula, why might we expect them to be at different stages of
evolution? What if this is a young cluster?
7. Which of these stars will move off the main sequence next? How do you know?
Questions for M44:
8. Which star in this cluster is the largest in size?
9. Which star(s), if any, have moved off the main sequence? If so, what is their
10. In comparing the two clusters, the Pleiades and M44, can you determine
which is the oldest cluster? How?
11. In what way did you have to consider their distances from our solar system in
making this determination of relative age between these two clusters?
12. Which star is the most luminous? Which is the brightest when viewed from
Discuss what you have learned about using the H-R Diagram to categorize stars,
and summarize what you now know about these two open clusters. Discuss the
characteristics of stars that influence their position and evolution on the H-R
Diagram, and why is the H-R diagram so useful in categorizing stars.
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PART II: BINARY STAR SYSTEMS (25 POINTS)
“Almost half of all stars are in binary star systems.” Let’s test it!
1.Open Stellarium. Turn on “Constellation Lines” (shortcut key “C”).
2.Choose TEN constellations.
3.For each constellation, click on each of its major stars (i.e., those
connected by lines).
4.Determine if each star is a binary star (double star).
5.Calculate the fraction of stars in binary systems (note: double stars
count two, while single star counts one).
6.Make a table with four columns: (1) constellation; (2) total number of
stars; (3) number of stars in binary systems (again, one binary
system contains two stars); (4) fraction of stars in binary systems.
Submit the table.
7.Calculate the average fraction of the ten constellations (i.e., average
of above Column (4)). Report the value.
8.Calculate the fraction of the whole sample (i.e., add all stars from
the ten constellations together). Report the value.
9.Answer the following questions.
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(Note: Answers to “why” should not be “because the lab asks me to do so”.
Think about the scientific reasons!)
1.What’s your reason of choosing your ten constellations?
2.Why do we choose ten constellations (i.e., why not two, and why not
3.Why do we choose constellations rather than star clusters?
4.Why do we only use the major stars (i.e., why not other fainter stars)
of the constellations?
5.Are your results (the two values of the fraction) from above Step 7
and 8 consistent? What could be the reason of that?
6.Find a classmate in Astron 1010 who is doing the same lab BUT
choose some different constellations (it’s ok to have some
constellations being the same — but should have some different).
Compare your results of Step 7 and 8 with your classmate’s. Are
they same? What’s the reason of being same or not? Write down
the name of your classmate and his/her 10 constellations. (If you
cannot find a classmate, talk to me.)
7.Is your result supporting or against the statement in the beginning of
this part? If not, what’s the possible reasons?
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APPENDIX: A FEW HELPFUL SHORTCUTS FOR STELLARIUM
A: Turn on/off Atmosphere
G: Turn on/off Ground
L: Increase time speed (cumulative)
J: Decrease time speed (cumulative)
K: Set speed back to normal
Space: Center on selected object
Mouse scroll: Change field of view
F3: Search for object
F5: Set Date/Time
Arrow Keys: Look Right/Left/Up/Down
C: Constellation lines
V: Constellation labels
F4 then under Markings -> Constellations -> borders: Constellation
Alt+tab: Return to desktop without closing program
(this works only on Windows)
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