Download Astronomy Exam #4

Astronomy Exam #4: Stellar Nomenclature
Name________________________________
Answer all questions on the exam in the provided spaces.
Refer to these stars in the table below in answering the following questions. There may be more than one
correct answer to some of the following questions. Choose all that apply.
Spectral
Luminosity
Star
m
M
Type
Class
A
B
C
D
E
-0.3
1.36
1.29
11.05
0.91
-0.3
-6.8
-5.2
15.5
-3.6
K2
O9
A2
M5
B1
III
I
II
V
V
1. Which of the stars listed above is appears the dimmest?________
2. Which of the stars listed above is the most luminous? ________
3. Which of the stars listed above is the hottest? ________
4. Which of the stars listed above is the largest in radius? ________
5. Which of the stars listed above is the closest? ________
6. Which of the stars listed above is 10 parsecs away? ________
7. Which of the stars listed above is a main sequence star? ________
8. Which of the two stars D or E is closer? ________
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9. A 10th magnitude star is ____ than a 5th magnitude star.
A. 2 times brighter
B. 2 times fainter
C. 100 times brighter
D. 100 times fainter
10. There are reported to be about 6,000 stars visible to the naked eye. How many of those stars would you
expect to be part of a multiple star system?
A. None
B. 100
C. 1,000
D. 3,000
E. 5,000
The HR Diagram at right is provided to assist with answering the following two questions.
11. Which is hotter, a main sequence star with an absolute magnitude of M= 4 or a white dwarf with a
luminosity 100 times smaller than the Sun?
A. the main sequence star
B. the white dwarf
C. They have the same temperature.
α
D. There is insufficient information to determine this.
12. Which of the statements below is true regarding the two stars marked
α and β?
β
A. Star α is hotter than star β.
B. Star α is less luminous than star β.
C. Star α is larger in radius than star β.
D. Star α appears brighter that star β.
γ
13. Which of the statements below is true regarding the two stars marked α and γ?
A. Star α is less luminous than star γ.
B. Star α has a longer main sequence lifetime than star γ.
C. Star α appears brighter that star γ.
D. Star α is larger in radius than star γ.
14. Which statement is the most correct about the comparison between a K5 main sequence star and a B5 main
sequence star?
A. The K5 star is cooler, less luminous, smaller, and will not live as long as the B5 main sequence star.
B. The K5 star is hotter, less luminous, larger, and will live longer than the B5 main sequence star.
C. The K5 star is smaller, hotter, more luminous, and will not live as long as the B5 main sequence star.
D. The K5 star is hotter, more luminous, smaller, and will live longer than the B5 main sequence star.
E. The K5 star is less luminous, cooler, smaller, and will live longer than the B5 main sequence star.
------------------------------------------------------------------------------------------------------------------------------The most common type of star in our Milky Way Galaxy is an M main sequence star. Assume that an M5 main
sequence star has an absolute magnitude of 16 to answer the following questions in a sentence or two.
15. What would be the apparent magnitude of an M5 main sequence star if it were 32.6 lyrs away from the Earth?
Explain your answer in a sentence.
16. What would be the apparent magnitude of an M5 main sequence star if it were 0.1 pc away from the Earth? Explain
your answer in a sentence.
17. Would an M5 main sequence star be visible to the naked eye if it were 0.1 pc from Earth. Answer yes of no and
explain your answer in a sentence below.
This is a” thinking” question: Star A appears brighter than Star B, but Star A actually gives off less energy than
Star B. The apparent magnitude and absolute magnitudes for Star A are m = 1 and M = -2, respectively. Use
this information to answer the following two questions.
18. Which of the following are the best possible values for the apparent and absolute magnitudes of Star B?
A. m = -1 and M = 2
C. m = 3 and M = 2
B. m = -1 and M = -4
D. m = 3 and M = -4
19. Which is the most correct statement about the distance of Star A from Earth?
A. Star A is closer than 10 pc from Earth.
B. Star A is exactly 10 pc from Earth.
C. Star A is farther than 10 pc from Earth.
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Imagine you are comparing the five stars (A-E, shown below) of different radii and temperatures. The
temperature of each star is indicated by a shade of gray (as shown at right), such that the lighter the shade of
gray, the higher the temperature of the star.
High
Medium
A
B
C
D
Low
E
20. Which of the following is the most correct ranking for the luminosity of these stars from greatest to least?
A. E= B > C =B > A
B. C > E > B >A > D
C. E > C> A >B > D
D. E = B> C =D > A
E. E > B > D>C > A
The asterism known as the Big Dipper has a very familiar shape today. However, in about 100,000 years the Big Dipper
will have a substantially different shape. See figures below.




100,000 yr



21. Why is the shape of the Big Dipper going to change in the next 100,000 years? Select the correct response from the
choices below.
A. The Earth’s movement with the Sun around the center of the Milky Way galaxy will change our viewpoint of the
stars in the Big Dipper. Since the stars are at different distances, the shape of the asterism will change as our
viewpoint changes.
B. The change in shape is just an illusion caused by viewing the stars from a moving platform – the Earth.
C. Some of the stars in the Big Dipper have extreme radial velocities that cause its shape to change.
D. The stars in the Big Dipper are being replaced with new stars as the old stars die off, thus changing the shape of
the asterism.
E. The stars in the Big Dipper have different proper motions that cause the shape to change.
22. A star is observed to have a stellar parallax angle of 0.037”. What is the distance to the star? Show your work.
23. The picture below portrays a proposed new space mission to establish a Hipparchus-like spacecraft in orbit around
Jupiter for the purpose of measuring stellar parallaxes. In a couple of sentences, explain why a mission like this
would be superior to the original Hipparchus spacecraft in orbit around the Earth during the early 1990’s.
Proposed orbit of new
spacecraft orbiting
Jupiter
Jupiter
Nearby star
Earth
Sun
The following question requires a
detailed quantitative answer.
24. Describe the nature of the bright stars in
the night sky, contrasting their
properties with the Sun. Be
quantitative in your description. An
HR diagram of the 300 brightest stars in
the sky appears to the right to assist
your memory.
25. You may have heard it said that the Sun is a
“typical” star. Please make an argument
below to either support or refute this statement
citing specific characteristics of the Sun and
the most common stars as represented by the
properties of the nearby stars. Be quantitative
in your description. An HR diagram of the
100 nearest stars in the sky appears to the right
to assist your memory.
Please solve the following numerical problem. Clearly show how you have arrived at your result. The points
awarded will be based on how clearly you have demonstrated good problem solving practices.
26. An O star is known to be eight times the temperature of the Sun and fivr times its radius. What is its
luminosity? You may answer either in Watts or in units of solar luminosity. Note: the radius of the Sun is
696,000 km and the temperature of the Sun is 5,800 K.
Physical Constants and Formulas
t
d
v
4
VSphere  R 3
3
GM
vOrbital 
R
2GM
R

A
L


2D
360
v Escape 
M
D (parsecs) 
4 2 r 3

G P2
Density 
1
p (arcsecond s)
Mass
M

Volume 4 3
R
3
M
years, where M and L are in solar units.
L
Stephan Boltzmann Law L  4R 2  T 4
Main Sequence Lifetime T  1010 
Wien' s Law T (K) 
3 10 6
Max nm 