Astronomy_103_Exam_2_practice_fall2023
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Astronomy
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Dec 6, 2023
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ASTRONOMY 103 EXAM 1 – VERSION A
Name (Print): Practice exam
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Signature:
Do not open the exam until told to do so.
You will have 75 minutes to complete the examination.
NO CELL PHONES, INTERNET, TEXT MSG, etc. ALLOWED AT ANY TIME.
Before the exam begins:
•
Print and sign your name, and write your student PID number in the spaces above and on the bubble
sheet.
During the exam
•
Mark your answers by filling in the appropriate bubble on the bubble sheet.
Only fill in one bubble
for each question.
•
If you are confused by a question, raise your hand.
A proctor will try to clarify without giving away
the answer.
If you are still stuck, move on to the next question and come back to the one that is
confusing you later.
•
You may write on your exam book.
However, none of this work will be graded.
Only the bubble
sheet will be graded.
•
The last page of the exam has some equations and constants.
You are welcome to rip off this last
page during the exam.
ASTR 103
Practice
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Astronomy 103, Exam 3 – Version A
2
Answer key for Fall 2023 practice exam:
1 d
2 e
3 d
4 e
5 a
6 b
7 d
8 c
9 b
10 e
11 a
12 c
13 a
14 b
15 b
16 e
17 d
18 a
19 a
20 d
21 c
22 a
23 b
24 e
25 c
26 c
27 c
28 d
29 b
30 e
31 b
32 c
33 b
34 b
35 a
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Astronomy 103, Exam 3 – Version A
3
1.
Photosynthetic organisms first evolved on Earth around 2 Gyr ago.
Which of the following events
happened as a result of the appearance of these organisms?
a.
The amount of carbon dioxide in the atmosphere dropped, reducing Earth’s natural greenhouse
effect and causing the “snowball Earth” with ice at or near the Equator.
b.
Global oxygen levels rose, killing many organisms adapted to live in an oxygen-poor world.
c.
The “great dying” mass extinction event began at the end of the Permian.
d.
both choice a and choice b
e.
all of choices a-c
2.
Which of the following are required in order for natural selection to occur?
a.
Individuals in a population must exhibit variation in one or more traits.
b.
Traits in which variation occurs must be heritable.
c.
Inherited traits must affect the ability of an individual to survive and reproduce.
d.
More than one of the above, but not all of the above, are required for natural selection.
e.
All of the above are required for natural selection.
3.
Which of the follow correctly describes why many astronomers look for alien signals in the radio part
of the spectrum?
a.
Radio light is less likely than other forms of light to be absorbed by a planet’s atmosphere and the
gas and dust between stars.
b.
Radio telescopes, unlike visible-light telescopes, can be used both day and night.
c.
A planet with a technological civilization could easily put out more radio light than that
civilization’s star.
d.
All of the above are correct.
e.
None of the above are correct.
4.
There have been five major mass extinction events during Earth’s history.
Which of these events was
likely caused by an asteroid colliding with Earth?
a.
the event at the end of the Ordovician
b.
the event in the late Devonian
c.
the event at the end of the Permian
d.
the event at the end of the Triassic
e.
the event at the end of the Cretaceous
5.
The Cambrian Explosion occurred 539 Myr ago.
For what percentage of its history did the Universe
exist prior to the Cambrian Explosion?
a.
96%
b.
75%
c.
25%
d.
4%
e.
less than 1%
6.
Imagine that a team of astronomers wants to resolve a continent on a planet orbiting the nearest star to
the Sun.
From our vantage point on Earth, the continent has an angular size of 4 x 10
-11
radians.
The
largest telescope available to the astronomers has a diameter of 10 m and they are observing the
planet in light of wavelength 1 x 10
-6
m.
Will the astronomers succeed?
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Astronomy 103, Exam 3 – Version A
4
a.
No, they would need a telescope with a diameter of 3.1 x 10
16
m.
b.
No, they would need a telescope with a diameter of 30,500 m.
c.
Yes, they could have resolved the continent with a telescope whose diameter is only 6.1 m.
d.
Yes, they could have resolved the continent with a telescope whose diameter is only 4.9 x 10
-5
m.
e.
Yes, they could have resolved the continent with a telescope whose diameter is only 3.1 x 10
-5
m.
7.
Imagine an alien civilization is attempting to directly image the inner planets in our Solar System.
In
what part of the electromagnetic spectrum should they look if they want the planets to be at their
maximum brightness compared to the Sun?
a.
gamma rays
b.
ultraviolet
c.
visible
d.
infrared
e.
radio
8.
You detect a radio signal at a particular frequency.
You notice that the signal was modulated up and
down around that frequency by 10 Hz.
You translate the parts that were modulated up by 10 Hz into
ones and the parts that were modulated down by 10 Hz into zeros.
Doing so gives you the following
string of 21 numbers:
0 0 0 0 1 0 1 1 1 0 1 0 1 0 1 1 0 1 0 0 0
21 is a semiprime number (i.e., it is what you get when you multiply together the prime numbers 3
and 7).
Using this information, what does the signal represent?
a.
It is the word “HI.”
b.
It is the word “IT.”
c.
It is a (rough) picture of a human.
d.
It is a picture of a pyramid.
Questions 9 and 10 refer to the timeline of the Universe shown below.
9.
Which letter (a-d) most accurately marks the time when our Solar System formed?
Choose “e” if you
think we need an arrow even closer to the “Now” line than it is possible to show on this scale.
10.
Which letter (a-d) most accurately marks the time when our species (Homo sapiens) first appeared on
Earth.
Choose “e” if you think we need an arrow even closer to the “Now” line than it is possible to
show on this scale.
The Big Bang
13.8 Gyr ago
Now
a
b
c
d
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Astronomy 103, Exam 3 – Version A
5
11.
Mammal species tend to exist for about 1 million years before going extinct.
If there are, on average,
0.2 fossils per species per million years, then how many fossils will our species (Homo sapiens) leave
if it lasts 1 million years?
a.
less than 1
b.
500
c.
200,000
d.
5 x 10
6
e.
2 x 10
7
12.
The graph at right shows the main sequence lifetime versus star
mass.
If we assume that intelligent life typically requires 5 Gyr
to evolve, then what is the mass of the largest star that could be
orbited by a planet inhabited by intelligent life.
a.
0.2 solar masses
b.
1 solar mass
c.
1.2 solar masses
d.
2 solar masses
e.
None of the stars represented on this graph have main
sequence lifetimes as long as 5 Gyr.
13.
Which of the following types of main sequence stars are the least likely to have planets on which
intelligent life evolves?
a.
O-type stars, because their main sequence lifetimes are too short for much evolution to occur.
b.
G-type stars, because they have so many stellar flares that any habitable planets are likely to have
their ozone layers destroyed.
c.
K-type stars, because they do not have enough stellar flares for abiogenesis to occur.
d.
M-type stars, because they are too cool to have habitable zones.
Questions 25-27 refer to the graph at right, which shows the frequency of impacts versus the amount of
energy released by an impact (in megatons of TNT).
14.
Over the next decade, what is the largest impact (in terms of the
energy released) that Earth is likely to experience?
a.
1/100
th
megaton of TNT
b.
1/10
th
megaton of TNT
c.
1 megaton of TNT
d.
10 megatons of TNT
e.
100 megatons of TNT
15.
There are 100 billion stars in the galaxy, and perhaps 10% have
Earth-like worlds. If those worlds have similar impact rates to the
Earth, how often do Tunguska-sized events happen in the galaxy?
a.
100 million Tunguska-sized events per year
b.
10 million Tunguska-sized events per year
c.
1 million Tunguska-sized events per year
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Astronomy 103, Exam 3 – Version A
6
d.
1000 Tunguska-sized events per year
e.
100 Tunguska-sized events per year
16.
The graph at right shows the brain weight (in grams)
versus body weight (in kg) for several types of animals.
Which of the following is a correct statement about the
ratio of brain weight to body weight (i.e., brain weight
divided by body weight)?
a.
Of all the animals shown, humans have the largest
ratio of brain weight to body weight since their data
point is the farthest from the black line.
b.
Of all the animals shown, sperm whales have the
largest ratio of brain weight to body weight since their
data point is the highest up on the graph.
c.
Of all the animals shown, blue whale have the largest ratio of brain weight to body weight since
their data point is close to that of sperm whales, which have a smaller mass than blue whales.
d.
Of all the animals shown, African elephants have the largest ratio of brain weight to body weight
since their data point is the one that is the highest while also being on the black line.
e.
None of these statements are correct.
Questions 17 and 18 refer to the following situation: Imagine we receive a radio signal from an
extraterrestrial civilization orbiting a star 25 light-years from Earth.
17.
If we immediately sent a response (via radio), how much time would pass for the extraterrestrials
between the moment they sent their signal to the moment their receive our response?
a.
less than 25 years
b.
25 years
c.
more than 25 years but less than 50 years
d.
50 years
e.
more than 50 years
18.
If we sent our response on a spacecraft, instead of by radio, then how long would it take our
spacecraft to reach the extraterrestrials if it were traveling at 20 km/s?
a.
376,000 years
b.
1.50 x 10
8
years
c.
3.76 x 10
8
years
d.
1.50 x 10
11
years
e.
none of the above
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Astronomy 103, Exam 3 – Version A
7
19.
A team of astronomers searching for radio signals from an extraterrestrial civilization is trying to
decide which of four stars they should focus on.
Based on what we know about stellar evolution,
stellar habitable zones, the timescales involved for the evolution of life on Earth, and the different
types of planets (terrestrial and giant), which star should the astronomers target if they want to find
intelligent life on a terrestrial planet?
a.
Star A
b.
Star B
c.
Star C
d.
Star D
20.
The current world population is about 8 billion. The world population in the year 1900 was about 2
billion. Assuming innovation proceeds at the pace of total brainpower of the human species, how
many years of 1900-era technological advancement could be done in one year today?
a.
10
b.
8
c.
6
Star A
Spectral Type: M
Current Age: 6 Gyr
Total Main-Sequence Lifetime: 90 Gyr
Habitable Zone: 0.21 AU-0.52 AU from star
Planets orbiting Star A
planet
distance (AU)
radius (Earth radii)
a
0.10
0.06
b
0.31
0.95
c
0.49
0.87
d
5.8
91
Star B
Spectral Type: M
Current Age: 1 Gyr
Total Main-Sequence Lifetime: 90 Gyr
Habitable Zone: 0.21 AU-0.52 AU from star
Planets orbiting Star B
planet
distance (AU)
radius (Earth radii)
a
0.20
210
b
0.35
395
c
0.67
42
d
1.1
2.9
Star C
Spectral Type: G
Current Age: 9 Gyr
Total Main-Sequence Lifetime: 10 Gyr
Habitable Zone: 0.7-1.2 AU from star
Planets orbiting Star C
planet
distance (AU)
radius (Earth radii)
a
0.60
0.89
b
1.4
0.85
c
11
112
d
30
96
Star D
Spectral Type: K
Current Age: 1 Myr
Total Main-Sequence Lifetime: 50 Gyr
Habitable Zone: 0.4 AU-1.1 AU from star
Planets orbiting Star D
planet
distance (AU)
radius (Earth radii)
a
0.29
2.7
b
0.76
1.2
c
17
8.3
d
29
41
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Astronomy 103, Exam 3 – Version A
8
d.
4
e.
2
Questions 21-24 refer to the table at right and the following information: You
observe four identical stars (A-D).
There is an absorption line in their spectra
that should occur at a wavelength of 656 nm for stars at rest.
The table shows the
wavelengths at which you find this absorption line in the four stars.
21.
Which star is moving the fastest toward or away from Earth?
a.
Star A
b.
Star B
c.
Star C
d.
Star D
e.
There is not enough information to tell.
22.
Are there any stars that could be moving side-to-side relative to Earth, but not toward or away from
Earth?
a.
Star A
b.
Star B
c.
Star C
d.
Star D
e.
This is not possible for any of the stars listed in the table.
23.
How many stars are experiencing a redshift in their spectrum?
a.
just 1
b.
2
c.
3
d.
all 4
e.
There is not enough information to tell.
24.
Which of the following correctly ranks the stars based on their distances from Earth, from farthest to
closest?
a.
Star C > Star A > Star D > Star B
b.
Star B > Star D > Star A > Star C
c.
Star B > Star D > Star C > Star A
d.
Star D > Star B > Star C > Star A
e.
There is not enough information to tell.
25.
Imagine you detect an exoplanet orbiting an F-type star.
The star’s radius is 903,000 km and the
planet blocks a maximum of 0.32% of the star’s light.
What is the radius of the planet?
a.
2900 km
b.
290000 km
c.
51,000 km
d.
510,000 km
Star
Wavelength
A
656 nm
B
660 nm
C
646 nm
D
657 nm
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Astronomy 103, Exam 3 – Version A
9
Questions 26-28 refer to the figure below, which shows four planets that each orbit a star identical to the
Sun at a distance of 1 AU.
26.
Which planet should have the greatest amount of erosion due to wind?
a.
Planet A
b.
Planet B
c.
Planet C
d.
Planet D
e.
There is not enough information to tell.
27.
Which planet should have the greatest amount of tectonic activity?
a.
Planet A
b.
Planet B
c.
Planet C
d.
Planet D
e.
There is not enough information to tell.
28.
Which planet should have the greatest number of visible impact craters?
a.
Planet A
b.
Planet B
c.
Planet C
d.
Planet D
e.
There is not enough information to tell.
29.
The figure at right, a planet is moving right to left across its star, as seen from
Earth.
Below is the light curve of the star.
Five points are labeled on the light
curve (a-e).
Which point corresponds to the instant in time shown on the figure at
right?
day length = 20 hours
radius = 0.7 Earth radii
A
day length = 10 hours
radius = 0.7 Earth radii
B
day length = 10 hours
radius = 1.4 Earth radii
C
day length = 10 hours
radius = 0.35 Earth radii
D
planet
star
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Astronomy 103, Exam 3 – Version A
10
30.
Imagine you have just discovered two planets (A and B) orbiting the same star.
Planet B orbits
farther from the star with a semi-major axis that is 1.5 times bigger than the semi-major axis of Planet
A’s orbit.
You determined that the star and planets are 0.5 Gyr old and that Planet A just became
tidally locked to the star.
How many more years will pass before Planet B becomes tidally locked to
the star?
a.
0.75 Gyr
b.
2.0 Gyr
c.
2.3 Gyr
d.
5.2 Gyr
e.
5.7 Gyr
31.
The largest asteroid, Ceres, has no atmosphere, an albedo of 0.090, and is 2.77 AU from the Sun.
What is the surface temperature of Ceres?
a.
91.6 K
b.
163 K
c.
167 K
d.
97,260 K
e.
2.0 X 10
6
K
32.
The graph at right shows the
radial velocity of a star versus
time.
The star is orbited by one
planet.
Which of the following
would be different if the planet
had a larger mass?
a.
The width of the curve would
get bigger.
b.
The width of the curve would
get smaller.
c.
The height of the curve
would get taller.
d.
The height of the curve
would get shorter.
e.
More than one of the above
changes would happen to the
graph.
time
brightness
a
b
c
d
e
height
of
curve
width of curve
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Astronomy 103, Exam 3 – Version A
11
33.
Choose the answer that best completes the following sentence: The Sun’s peak wavelength occurs in
the __ part of the spectrum and the two types of light that account for most of the Sun’s emitted light
are __.
a.
infrared; infrared and visible
b.
visible; infrared and visible
c.
visible; ultraviolet and visible
d.
infrared; ultraviolet and infrared
e.
ultraviolet; ultraviolet and visible
34.
The graph below shows the light curve of a star that is orbited by some planets.
Which of the following diagrams best represents the system of planets (black circles) orbiting the star
(yellow circle)?
Note: While the diagrams are not to scale, bigger planets are represented by larger
circles.
time
brightness
star
a.
star
b
.
star
c.
star
d.
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Astronomy 103, Exam 3 – Version A
12
35.
Which of the following statements correctly describes the
trend represented by the red line?
a.
More energetic stellar flares occur less often than less
energetic stellar flares.
b.
More energetic stellar flares occur more often than less
energetic stellar flares.
c.
More energetic stellar flares occur just as often as less
energetic stellar flares.
d.
There is no relationship between a stellar flare’s energy
and how often it occurs.
Useful numbers
1 AU =
150 million km
1 light-year =
9.46 x 10
15
m
speed of light c =
3.00 x 10
8
m/s = 300,000 km/s
1 solar luminosity =
3.38 x 10
26
W
Gravitational constant G =
6.67 x 10
-11
m
3
kg
-1
s
-2
Plank’s constant h =
6.63 x 10
-34
kg-m
2
/s
Radius of Sun:
700,000km = 0.00465AU
Radius of Earth:
6400km = 4.26x10
-5
AU
Mass of Earth:
6 x 10
24
kg
Sun’s surface temperature:
5770K
Stefan-Boltzmann constant σ = 5.67 x 10
-8
W m
-2
K
-4
Typical densities for materials making up planets:
Hydrogen:
1 g/cm
3
(when compressed in a gas giant atmosphere)
Water:
1 g/cm
3
Rock:
2-4 g/cm
3
Iron:
8-9 g/cm
3
flare energy
cumulative flares per day
ozone depletion zone
abiogenesis zone
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Astronomy 103, Exam 3 – Version A
13