Download ASTR 104 - Wagner Homework 1

ASTR 104 - Wagner
Homework 1
Instructions: Answer each question below completely. All answers must show your reasoning
and explanations. Any questions that involve a calculation must show your work. Incomplete
answers will not receive full credit! Remember, homework assignments are primarily graded on
effort, so make your attempt on each question. If you don’t answer a question, you get no
credit for it!
1. Explain exactly what a constellation is. How has the definition of a constellation changed
since ancient times? Why are constellations useful for mapping the sky?
2. We say that there are summer constellations and winter constellations. Explain why we
see different constellations at different times of the year. It can help to draw a sketch of
the Sun and Earth to show this.
3. There are two different types of eclipses: lunar and solar. Explain the position of the
Earth-Moon-Sun system for each type of eclipse. Also, explain why an eclipse does not
occur each month.
4. Given that the distance from the Earth to the Sun is 150,000,000km, through what
distance would the Earth move in a second? An hour? A day?
5. Given that the distance to the Moon is 384,000km, and taking the Moon’s orbit around
the Earth to be circular, estimate the speed (in km/sec) at which the Moon orbits the
Earth.
6. Galileo made a number of different discoveries with his telescope. List at least 5 of these
and explain which of them specifically supported the view of Copernicus that the Earth
was not the center of the universe.
7. Explain why we say that a baseball falls towards the Earth and not the Earth towards the
baseball. Is this really the correct thing to say? Explain what is really happening.
8. Explain what would happen to the Earth if the Sun’s gravity were suddenly to be turned
off.
9. Calculate how long it would take for a radar signal to complete a trip between Earth and
Mars when the two planets are 0.7AU apart.
10. An asteroid has a perihelion distance of 2.0AU and aphelion distance of 4.0AU. Calculate
its orbital semi-major axis, eccentricity and period.
ASTR 104 - Wagner
Homework 2
Instructions: Answer each question below completely. All answers must show your reasoning
and explanations. Any questions that involve a calculation must show your work. Incomplete
answers will not receive full credit! Remember, homework assignments are primarily graded on
effort, so make your attempt on each question. If you don’t answer a question, you get no
credit for it!
1. Define each of the following wave properties: period, wavelength, amplitude &
frequency.
2. Suppose you are an astronomer on Venus where the clouds are always covering the sky.
How might you use your knowledge of the electromagnetic spectrum to learn about
objects beyond the clouds? Which types of radiation might penetrate the clouds to
reach the ground?
3. Why do atoms absorb and reemit radiation at characteristic frequencies?
4. Explain how astronomers use the Doppler Effect to determine the velocities of
astronomical objects.
5. Normal human body temperature is about 37oC. Convert this temperature to Kelvins.
What would be the peak wavelength emitted by a person with this temperature? In
what part of the electromagnetic spectrum does this lie?
6. What advantages does the Hubble Space Telescope have over ground based telescope?
What are the disadvantages of having a telescope in space?
7. What is the primary factor that limits the clarity of a ground based optical telescope?
What are some (more than one!) methods that astronomers have used to overcome this
limitation?
8. What are the advantages of being able to study an object at many different wavelengths
of radiation? How did this limit our knowledge of the universe a hundred years ago?
9. Explain what we mean by interferometry. What problem that exists in radio astronomy
does it address?
10. A 2-meter telescope can collect a given amount of light in one hour. Under the same
observing conditions, how long would it take for a 6-meter telescope to perform the
same task? How about a 12-meter telescope?
ASTR 104 - Wagner
Homework 3
Instructions: Answer each question below completely. All answers must show your reasoning
and explanations. Any questions that involve a calculation must show your work. Incomplete
answers will not receive full credit! Remember, homework assignments are primarily graded on
effort, so make your attempt on each question. If you don’t answer a question, you get no
credit for it!
1. Name three important differences between the Terrestrial and Jovian Planets.
2. Explain how the Moon produces tides in the Earth’s oceans. What part does the sun
play in producing the tides?
3. How did radio observations of Venus made in the 1950s change our conception of
the planet?
4. How was the planet Uranus discovered? Explain the difference in this discovery and
the way Neptune was discovered.
5. Explain how and why the density of the Galilean satellites changes as you move
away from Jupiter. What causes this variation and how is it related to the solar
system formation?
6. List the major regions of the sun and briefly describe each one.
7. We have said that some of the energy in the sun is transported by convection. What
evidence do we have that this is the case?
8. Explain the ingredients and the end products of the proton-proton chain. Why does
this process release energy?
9. Why was the solution of the “Solar Neutrino Problem” important to both
astronomers and physicists? What did it tell each of the two groups of scientists?
10. What would we observe on Earth if the Sun’s internal energy suddenly shut off?
How long do you think it might take – minutes, days, years, millions of years – for
the sun’s light to begin to fade? We talked in class about the sun’s light taking 8
minutes to reach the Earth. This is NOT the same question. I am asking you to think
about how long it takes the energy to get from the center of the sun to the surface.
ASTR 104 - Wagner
Homework 4
Instructions: Answer each question below completely. All answers must show your reasoning
and explanations. Any questions that involve a calculation must show your work. Incomplete
answers will not receive full credit! Remember, homework assignments are primarily graded on
effort, so make your attempt on each question. If you don’t answer a question, you get no
credit for it!
1. Explain the difference between absolute and apparent brightness of a star.
2. In a few sentences, describe the how astronomer go about classifying stars by their spectral
characteristics.
3. Describe what astronomers mean by the “main sequence”. What are the two basic
properties of a star that tells us where it will lie on the “main sequence”.
4. Distances are a difficult thing to determine in astronomy. What is the direct method that
astronomers use to determine a distance to a star? How does it work? For more distant
stars, astronomers use a method called “spectroscopic parallax”. Explain how this method
works. What happens if there is dust between us and the star that we don’t know about
that causes it to appear fainter than it otherwise would?
5. We have learned that stars with larger masses has much more fuel that their lower mass
counterparts. This would make you think that they should live a longer life, right? But, we
find that the more massive stars actually live the shortest lives. Explain why.
6. Section 10-1 on page 273 of the text gives the equation to calculate the distance to a star is
we know its apparent and absolute magnitudes:
)
Astronomers call the term (m-M) the distance modulus of a star. What is the distance
modulus of a star at a distance of 10pc? More tricky, what is the distance to a star with an
apparent magnitude of +1.35 and an absolute magnitude of +5.70. You will need to use the
“inv log” function on a scientific calculator to do the final calculation.
7. An astronomer observes two stars, one has an absolute magnitude of 0 and the other an
absolute magnitude of 10. But, they both have the same apparent magnitude of 5. First,
explain which star is more distant and why. Now, use the equation from #6 to calculate how
much more distant the distant star is!
8. We talked about a number of different types of binary stars. There are three classes, which
is the most frequently observed of the three and why are the other two rarer?
ASTR 104 - Wagner
Homework 5
Instructions: Answer each question below completely. All answers must show your reasoning
and explanations. Any questions that involve a calculation must show your work. Incomplete
answers will not receive full credit! Remember, homework assignments are primarily graded on
effort, so make your attempt on each question. If you don’t answer a question, you get no credit for
it!
1. What is the difference between interstellar gas and interstellar dust? Explain what each
of these is made of.
2. Explain the differences between an emission nebula, a reflection nebula and a dark
nebula.
3. We discussed 21-cm radiation in class. What part of the electromagnetic spectrum is it
in? Why is it useful for astronomers to study this radiation?
4. Explain what we mean by an evolutionary track. How do astronomers use them to study
stars? During which stages of the evolutionary track must we use radio and infrared
radiation to study the stars?
5. What is the critical event that must occur in order for a protostar to become a star?
What happens to the protostar if this event does not occur?
6. Explain the difference in the death of a low-mass and a high-mass star?
7. What circumstances are necessary for a binary star to produce a nova? Could one occur
outside of a binary system?
8. What are the different phases that the sun will go through during its lifetime.
9. What are the two inventively named supernova types? Explain the difference between
each of them.
10. A main sequence star leaves the main sequence and ascends the giant branch. It
increases in radius by a factor of 100. It decreases temperature by a factor of 3. What
will happen to the luminosity? (LαR2T4). A more difficult question: By how much will its
apparent magnitude increase? (Remember that each magnitude is a factor of 2.5 in
brightness.)
ASTR 104 - Wagner
Homework 6
Instructions: Answer each question below completely. All answers must show your reasoning
and explanations. Any questions that involve a calculation must show your work. Incomplete
answers will not receive full credit! Remember, homework assignments are primarily graded on
effort, so make your attempt on each question. If you don’t answer a question, you get no
credit for it!
1. The first neutron stars that were discovered were all pulsars. Explain why we do not see ALL
neutron stars as pulsars.
2. A pulsar was observed to have a planetary system orbiting it. Explain why this was a great
surprise to astronomers.
3. Explain what we mean when we discuss the event horizon of a black hole.
4. The theory of general relativity has been around for about a hundred years now. Explain
why it is so difficult to test its predictions. Briefly describe two tests that have been done.
5. Describe the effects on the Earth if the sun were to be suddenly transformed into a black
hole of the same mass. What would be the effects on the Earth’s orbit and what would be
the effects on the Earth itself.
6. There are a great number of globular clusters scattered around our galaxy. The clusters tell
us a few things about our galaxy and our position in it. What are they?
7. We have talked about a few steps on the distance ladder. Another is Cepheid variable stars.
Explain how we use them to determine distances. What is the difference between these and
the RR Lyrae stars?
8. The center of our galaxy must emit a great amount of radiation at all wavelengths, including
the optical. Yet, it cannot be studied by optical astronomers. Explain why this is so.
9. We talk about star formation as occurring in and near the spiral arms. Why do we think this
is so? What evidence do we have?
10. We discussed the rotation curve of our galaxy. Why has it been a source of confusion to
astronomers in the past (and present!)? What does it tell us about the total mass of our
galaxy and how that mass is distributed?
ASTR 104 - Wagner
Homework 7
Instructions: Answer each question below completely. All answers must show your reasoning
and explanations. Any questions that involve a calculation must show your work. Incomplete
answers will not receive full credit! Remember, homework assignments are primarily graded on
effort, so make your attempt on each question. If you don’t answer a question, you get no
credit for it!
1. We discussed a number of different types of spiral galaxies. What is the primary difference
between the two classes? How do we categorize galaxies within each of these classes?
2. We have spent a good amount of time this semester on the distance ladder. Explain why
each step we take up on the ladder leaves us with more and more uncertainty in our
distance estimates.
3. Explain what we mean by Hubble’s Law and how we can use it to determine the distance to
a galaxy.
4. In chapter 15, we discussed both normal and active galaxies. What were the two basic
differences between these two types of galaxies?
5. I have told you that quasars are extremely luminous. Explain the evidence that we have that
this is correct.
6. We said that the Milky Way galaxy contained more mass than we could see. Why do we
think that the same is true of clusters of galaxies?
7. Briefly describe two techniques that we can use to determine the mass of a galaxy.
8. What evidence do we have that galaxies actually collide with each other. We never really
talked about stars colliding. Why do you think that galaxies collide quite often, but it is rare
for stars to collide?
9. What evidence do we see that tells us that there are black holes at the centers of many
normal galaxies? Is there differing evidence if we are talking about active galaxies?
10. Explain why we believe that quasars probably represent an early stage of galactic evolution.
ASTR 104 - Wagner
Homework 8
Instructions: Answer each question below completely. All answers must show your reasoning
and explanations. Any questions that involve a calculation must show your work. Incomplete
answers will not receive full credit! Remember, homework assignments are primarily graded on
effort, so make your attempt on each question. If you don’t answer a question, you get no
credit for it!
1. What are the two assumptions that we make in the “Cosmological Principle”? Are these
good assumptions, at least based on our current knowledge of the large scale structure of
the universe? Explain.
2. Explain what we mean by Olber’s paradox. What are the four assumptions that go into it
and which, if any, of those assumptions are incorrect. Explain how we know.
3. We started the class talking about the Earth at the center of the universe. Then it was the
sun. What is actually at the center of the universe? And, can you explain exactly where the
big bang did occur?
4. Why was the discovery of the cosmic background radiation so important? Explain what it
told us about the history and origin of the universe.
5. Explain what we mean by cosmic inflation. How does inflation solve both the horizon and
flatness problems?
6. We know we have organic molecules on the Earth. Is there anyplace else in the universe
where we have detected organic molecules? Explain.
7. When we talk about life in the universe, we tend to instinctively introduce a bias into the
discussion. Explain what this bias is. What conclusions might we come to if we could
overcome this bias?
8. We discussed the Drake Equation. List the main terms of the equation and tell how well we
know the value of each term.
9. What do we mean when we talk about the “Water Hole”? Explain why might this be a good
place to look for a sign of extragalactic intelligence?
10. Free question – Create a question about astronomy and answer it. Just make sure you get
the answer right!