Science Standards:
Energy & Matter, Systems & Interactions, Stability & Equilibrium
Objectives:
Materials:
brightness of star 1 = difference in magnitude
brightness of star 2 (2.512)
Using this sort of scale, we can actually describe the brightness of stars in real numbers. Really bright objects, like the full moon have a negative magnitude.
Object apparent magnitude
Sun -26.5
Full Moon -12.5
Venus -4.1
Sirius -1.4
North Star 2.0
limit of naked eye 6
Pluto 15
limit of HST 28
Astronomers also classify stars by their type of spectrum. Stars are
easily classified by the amount of hydrogen which they contain as revealed
to us by the intensity of their spectrum. Stars with the most hydrogen
are called A stars, the remaining letters designate varying amounts of
different chemical stellar compositions.
If we consider the temperature of stars, as revealed to us by their
color, we find that the O stars, are hottest, followed by B stars, A stars,
F, G, K, and M stars. A star which has an intermediate temperature between
an O star and a B star is called an O5 star. This layout of temperature
is given from hottest to coolest as:
O0, O1, O2, O3, O4, O5, O6, O7, O8, O9, B0, B2, B3, B4, B5, B6......
Astronomers sometimes humorously teach their students to remember this sequence from hottest to coolest as:
O h, b e a f ine g uy (or gal), k iss m e!
Our Sun is G2 star, which means that it is a rather intermediate temperature star.
Directions:
1. Plot most or all of the Near Stars on the HR Diagram.
2. Plot most or all of the Bright Stars on the HR Diagram using a different
color.
3. Compare the attributes of Near Stars and Bright Stars.
4. Characterize the nature and relative number of stars in our galaxy.
5. Summarize the evolution of a star.
6. Complete the Student Answer Sheets.
Description: Using the concepts of stellar brightness and color, you will graphically analyze the relationships between bright stars, near stars, temperature. This activity will culminate in the a description of how stars change over time.
Materials: graph paper (provided)
2 different colored pencils, pens, or crayons
Introduction: When you look up at the stars of the night-time
sky, you will immediately notice that all of the stars do not have the
same apparent brightness. What are several possible explanations for this
observation?
The brightness that a star has as seen from the Earth is called the apparent brightness . Stars which are very bright are called magnitude 1 stars . The next brightest are magnitude 2 stars. Then comes magnitude 3, 4, 5, and down to the very faintest stars visible with the naked eye, magnitude 6 stars.
By observing stellar parallax, we know that all stars are not the same distance away. Obviously, a star which is far away will appear dimmer than a similar star which is closer. We adjust for the distance of stars by giving stars an absolute brightness . The absolute magnitude of a star is the apparent magnitude that a star would have at a distance of 32.6 light years (10 parsecs).
Table 1 of this activity contains a list of 37 very bright stars. Table 2 of this activity contains a list of 30 stars near the Earth. Also provided on the table is the spectral class of each star (recall that the spectral class of each star tells us both the star's surface temperature and the amount of hydrogen it contains).
Procedure:
1. Using the list of Bright Stars in Table 1 and the list of Near Stars
in Table 2, plot their absolute magnitude vs. spectral class on
the attached graph. Use different colors for the near stars and for the
bright stars. (Ask your instructor if you should plot all of the stars
listed.)
2. What general trends or concentrations do you see in the data? Are
there generalizations you can make about bright stars? Any generalizations
about near stars?
3. This diagram was first published by Henry Norris Russell and Ejnar
Hertzsprung in the early 1900's. It is sometimes called a color - magnitude
diagram. Why is this ( or why is this not) an appropriate name it is a
plot of magnitude versus spectral class?
4. Our star, the Sun, is a G2 spectral class star with an absolute magnitude
of 4.8 . How does it compare to the locations of the Near Stars on the
diagram?
How does it compare to the locations of the Bright Stars on the diagram?
5. Which spectral class is most common?
6. Which spectral class is the least common?
7. In general, what is the relationship between the temperature of a
star and its brightness?
8. Most of the stars seem to be along a line from the upper left corner
to the lower right corner of the HR Diagram. Stars which fall into this
category of stars are called main sequence stars . Does our Sun
fit into this category?
9. Consider the rogue stars in the upper right hand corner and the lower
left hand corner. What are the bright cool stars? What are the hot dim
stars? (Compare your answer with the adjacent group.)
10. Stars which are "on the main sequence" are generally very stable
stars which are combining their hydrogen atoms into larger helium atoms
(this reaction is called fusion and gives off energy). Where in
the star do you think that this fusion reaction is most likely occurring?
Why?
Main sequence stars which are very bright are fusing hydrogen atoms
into helium atoms at an enormous rate. Do you think that these bright stars
will burn forever? How long do you think these stars will shine compared
to the dimmer main sequence stars?
11. Why is it that black holes do not appear on the HR Diagram?
12. As a group and as a group, discuss what you think might occur when
a star depletes its supply of hydrogen.
| Star Name |
|
|
Star Name |
|
|
| 1. Sirius A |
|
|
19. Aldebaran A |
|
|
| 2. Sirius B |
|
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20. Aldebaran B |
|
|
| 3. Canopus |
|
|
21. Crucis A |
|
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| 4. Centaurus A |
|
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22. Crucis B |
|
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| 5. Centaurus B |
|
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23. Antares A |
|
|
| 6. Arcturus |
|
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24. Antares B |
|
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| 7. Vega |
|
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25. Spica |
|
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| 8. Capella A |
|
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26. Pollux |
|
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| 9. Capella B |
|
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27. Fomalhaut A |
|
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| 10. Capella C |
|
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28. Fomalhaut B |
|
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| 11. Rigel A |
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29. Deneb |
|
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| 12. Rigel B |
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30. Beta Crucis |
|
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| 13. Procyon A |
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31. Regulus |
|
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| 14. Procyon B |
|
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32. Adhara |
|
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| 15. Achernar |
|
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33. Castor A |
|
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| 16. Beta Centari |
|
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34. Castor B |
|
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| 17. Betelgeuse |
|
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35. Castor C |
|
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| 18. Altair |
|
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36. Shaula |
|
|
| - |
|
|
37. Bellatrix |
|
|
| Star Name |
|
|
Star Name |
|
|
| 1. Sun |
|
|
16. Procyon A |
|
|
| 2. Centari A |
|
|
17. Procyon B |
|
|
| 3. Centari B |
|
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18. Struve 2398 |
|
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| 4. Centari C |
|
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19. Struve 23948 |
|
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| 5. Lalande 21185 |
|
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20. Groom 34 A |
|
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| 6. Sirius A |
|
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21. Groom 34 B |
|
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| 7. Sirius B |
|
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22. Lacaille 9352 |
|
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| 8. Ross 154 |
|
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23. Tau Ceti |
|
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| 9. Ross 248 |
|
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24. BD +5 1668 |
|
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| 10 Epsilon Eridani |
|
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25. Lacaille 8760 |
|
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| 11. Luyten |
|
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26. Kapteyn's Star |
|
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| 12. Ross 128 |
|
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27. Krueger 60 A |
|
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| 13. 61 Cygnus A |
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28. Krueger 60 B |
|
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| 15 61 Cygnus B |
|
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29. Ross 614 |
|
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| 15. Epsilon Indi |
|
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30. BD -12 4523 |
|
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INSERT Hertzsprung Russell Graph
FIGURE 107
HERE