H-R Diagram Lab
Note: Remember you are responsible for graphs, charts and other items that form part of the overall summary of this topic.
Vocabulary:
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luminosity: brightness – dependent on a star’s size; temperature and distance
spectral class: classification of stars by their spectrum and luminosity
magnitude: measure of the brightness of a star or other celestial objects
The development of the H-R Diagram began with Danish astronomer Ejnar Hertzsprung who began plotting the stars around
1911. American astronomer Henry Norris Russell independently developed his own diagram. These two scientists independently
discovered that comparing magnitudes and spectral class (color) of stars yielded a lot of information about them. Together, they
created a diagram on which they mapped stars by magnitude and spectral class.
After the astronomers had completed graphing the stars, they noticed that several patterns appeared. First, they noticed that ninety
per cent of the stars fell along a diagonal line from the top-left corner to the bottom-right corner. These are called main sequence
stars, of which our Sun is a member. Another pattern they noticed was that the Cepheid’s (class of variable stars that brighten and
dim in a regular fashion); giants; super-giants and dwarfs fell into groupings quite separate from the main sequence stars. The
white dwarfs were on the bottom-left; the red super-giants were in the upper-right; red giants were on the diagonal that those two
made; blue giants were slightly to the right of the start of the main sequence; Cepheid’s were in the upper middle.
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Objective:
Investigate the relationship between stars temperature, brightness and diameter.
Background:
The H-R diagram is a graph of star brightness versus star temperature. When many stars are plotted on an H-R diagram, it is found
that they fall into groups. These groupings indicate star sizes and are clues to how the stars change during their lifetime. The
measure of star brightness used in the H-R diagram is termed absolute magnitude. A star’s absolute magnitude is not affected by
its distance from Earth. The smaller the absolute magnitude, the brighter the star. The very brightest stars have negative
magnitudes.
Materials:
Pencil, graph paper
Procedure:
1.
2.
3.
4.
5.
6.
7.
Using the graph below, plot the stars from Group 1.
Once you have plotted the stars from Group 1, answer the following questions. Label this group of questions as “Group 1
Questions.”
a. What would you tell someone who thinks that all stars are very similar (be sure to discuss temperature and
brightness)?
b. How does our sun compare to other stars in brightness and temperature?
c. Are the stars scattered randomly on the graph, or is there a pattern? Explain.
d. Would you expect hotter stars to be dim or bright? Does the graph agree with this answer?
Using the same graph, plot the stars from Group 2.
Once you have plotted the stars from Group 2, answer the following questions. Label this group of questions as “Group 2
Questions.”
a. Do the Group 2 stars follow the same pattern as the Group 1 stars that you plotted? Explain.
b. Overall, are the stars in Group 2 very bright or very dim?
c. Are these stars hot or cool compared to other stars?
d. Is the relationship of brightness to temperature for these stars puzzling, or does it make sense? Explain.
Using the same graph, plot the stars from Group 3.
Once you have plotted the stars from Group 3, answer the following questions. Label this group of questions as “Group 3
Questions.”
a. Compare the areas of the graph where the Group 2 and Group 3 stars are plotted. How are they different?
b. Overall, are the stars in Group 3 very bright or very dim?
c. Are these stars hot or cool compared to other stars?
d. Is the relationship of brightness to temperature for these stars puzzling, or does it make sense? Explain.
Conclusion – you may wish to consult your textbook and use the internet to assist in answering the following questions.
a. As you can see from the Group 1 stars, the cooler or hotter a star is, the brighter the star. The Group 2 and Group
3 stars do not follow this pattern. Hence, there must be something besides temperature that can affect the
brightness of stars. Describe your own theory about these stars (Group 2 and Group 3). Why would their
brightness not be strictly related to their temperature?
b. What is the "Main Sequence?"
c. Label the Main Sequence on your H-R Diagram.
d. What percent of all stars are on the Main Sequence?
e. Label “dwarfs" and "giants" on your H-R Diagram.
f. Explain the process of Nuclear Fusion.
g. Why is the process of nuclear fusion important?
h. Summarize the history and probable future of our sun (a main sequence star). How did it begin and how will it
end its life cycle? Be sure to include the following terms in your discussion: nebula; fusion; gravity; giant; white
dwarf.
i. Define the following terms: super-giant; supernova; neutron star; black hole.
j. What determines if a star will end its life as a white dwarf, a neutron star or a black hole?
k. At the beginning of the universe, scientists believe it contained only what two elements?
l. Where were all of the other elements formed?
m. Why aren’t the Group 2 and Group 3 stars not on the Main Sequence?
Group 1
Visual Magnitude
(Apparent)
Distance
(light-years)
Temperature
(Kelvin)
Luminosity
(Sun = 1)
(Absolute)
* Sun
1
-26.7
0.00002
5,800
1.00
* Alpha Centauri A
2
-0.01
4.3
5,800
1.5
* Alpha Centauri B
3
+1.4
4.3
4,200
0.33
* Alpha Centauri C
4
+11.0
4.3
2,800
0.0001
* Wolf 359
5
+13.66
7.7
2,700
0.00003
* Lalande 21185
6
+7.47
8.1
3,200
0.0055
* Sirius A
7
-1.43
8.7
10,400
23.0
* Luyten 726-8 A
8
+12.5
8.7
2,700
0.00006
* Luyten 726-8 B
9
+12.9
8.7
2,700
0.00002
* Ross 154
10
+10.6
9.6
2,800
0.00041
* Ross 248
11
+12.24
10.3
2,700
0.00011
* Epsilon Eridani
12
+3.73
10.8
4,500
0.30
* Ross 128
13
+11.13
11.0
2,800
0.00054
* 61 Cygni A
14
+5.19
11.1
4,200
0.084
* 61 Cygni B
15
+6.02
11.1
3,900
0.039
* Procyon A
16
+0.38
11.3
6,500
7.3
* Epsilon Indi
17
+4.73
11.4
4,200
0.14
* Vega
18
+0.04
26.0
10,700
55.0
* Achernar
19
+0.51
65.0
14,000
200.0
* Beta Centauri
20
+0.63
300.0
21,000
5,000.0
* Altair
21
+0.77
16.5
8,000
11.0
* Spica
22
+0.91
260.0
21,000
2,800.0
* Delta Aquarii A
23
+3.28
84
9,400
24.0
* 70 Ophiuchi A
24
+4.3
17
5,100
0.6
* Delta Persei
25
+3.03
590
17,000
1,300.0
* Zeta Persei A
26
+2.83
465
24,000
16,000.0
* Tau Scorpii
27
+2.82
233
25,000
2,500.0
Visual Magnitude
(Apparent)
Distance
(light-years)
Temperature
(Kelvin)
Luminosity
(Sun = 1)
(Absolute)
* Arcturus
28
-0.06
36.0
4,500
110.0
* Betelgeuse
29
+0.41
500.0
3,200
17,000.0
* Aldebaran
30
+0.86
53.0
4,200
100.0
* Antares
31
+0.92
400.0
3,400
5,000.0
* Delta Aquarii B
32
+2.86
1030
6,000
4,300.0
Group 2
Group 3
Visual Magnitude
(Apparent)
Distance
(light-years)
Temperature
(Kelvin)
Luminosity
(Sun = 1)
(Absolute)
* Sirius B
33
+8.5
8.7
10,700
0.0024
* Procyon B
34
+10.7
11.3
7,400
0.00055
* Grw +70 8247
35
+13.19
49
9,800
0.0013
* L 879-14
36
+14.10
63?
6,300
0.00068
* Van Maanen's Star
37
+12.36
14
7,500
0.00016
* W 219
38
+15.20
46
7,400
0.00021
* Barnard's Star
39
+9.54
6.0
2,800
0.00045
* Luyten 789-6
40
+12.58
11.0
2,700
0.00009
* Canopus
41
-0.72
100.0
7,400
1,500.0
* Capella
42
+0.05
47.0
5,900
170.0
* Rigel
43
+0.14
800.0
11,800
40,000.0
* Alpha Crucis
44
+1.39
400.0
21,000
4,000.0
* Fomalhaut
45
+1.19
23.0
9,500
14.0
* Deneb
46
+1.26
1,400.0
9,900
60,000.0
* Beta Crucis
47
+1.28
500.0
22,000
6,000.0