Astr 222 Practice Midterm #1
5 questions similar in style to the ones below
Each question is worth 5 points.
Your answer should be a short paragraph long for each.
- Describe what is meant by Population I objects and
Population II objects. Give examples.
- Describe the Magellenic Clouds.
- Why do we believe there is a lot of dark matter in
- Describe what is meant by the "luminosity function" of galaxies.
In this context, what is L*? Sketch what this function looks like.
- Why does the X-ray variability of the galactic center
place a limit on the size of the object at the center?
2 questions similar in style to the ones below.
Each question is worth 5 points.
Make sure to bring a stand-alone scientific calculator! No smartphones allowed.
- You are studying a distant star cluster, and find that
the stars appear too red for their spectral type -- their colors are too
red by 0.25 in B-V color. You also find that there is a Cepheid variable
star in this cluster, with a period of 10 days and a mean apparent V magnitude
of 7.0. How far away is the cluster?
- If your telescope can reliably measure the brightnesses
of stars down to 20th magnitude, what is the farthest away you could detect
a Cepheid variable? Remember that the most luminous Cepheids have period of
about 100 days.
One question, which will be taken from the list below.
The question is worth 15 points.
Your answer should be ~ 2-3 blue book pages long
- Describe the structure of the Milky Way Galaxy. Be
sure to talk about the properties and relative sizes of the different components
of the Galaxy. Where is the Sun's location in the Galaxy? A sketch will probably
be useful here!
- Describe the Great Debate. Make sure to explain
and evaluate the arguments on both sides -- whose evidence was flawed, and why? How did Edwin Hubble resolve
- Sketch the Hubble Sequence, defining the
different classification terms and how galaxies are classified. What
kind of galaxy is the Milky Way? What about the Large Magellenic Cloud?
- Describe the Oort Limit and sketch the rotation
curve of the Milky Way. Explain how both suggest that there is dark
matter in our Galaxy. Using those two arguments alone, also explain why
we believe the dark matter is in an extended halo rather than confined
in the disk or in the inner parts of the galaxy.
- Describe three different ways you could measure
distances to stars or star clusters in the Milky Way galaxy. For each
method, describe the data you would need, along with the advantages and
disadvantages to each method.
You will get a page of equations and constants with
the test, so you do not need to memorize constants or equations except for these three:
- the definition of magnitudes: m1-m2 = -2.5log(f1/f2) (m=mag, f=flux)
- the magnitude distance relationship: m-M = 5log10(d) - 5 (m=app mag, M=abs mag, d=distance in parsecs)
- the distance / angular size relationship: d = alpha * D / 206265 (d=physical size, D=distance, alpha=angular size in arcseconds)
- Study using your notes, the online course notes, and
the HW assignments and solutions. For more information on a topic,
review the textbook chapters given on the syllabus. (Note: you will not
be responsible for material in the textbook that is not in the course
- When answering questions, try to address both "what" and
"why" in your answer. That is, both describe/define whatever is being
asked about (that's the "what") and also give an explanation for how or
why something works (the "why").
- Sketches are useful, but if you are sketching a plot you
should always have axes labeled (i.e., "Time", "Apparent Magnitude",
etc). It's also a good idea to indicate which direction the values
increase (i.e., "the Y-axis is magnitude, with brighter objects to the
- When calculating something, if your answer doesn't make
sense, say so! ("I got a size for the Sun of 10 meters, which is crazy
small -- I must have done something wrong!"). Otherwise I would worry
that you don’t really understand how big the Sun really is...
- Also on calculations, SHOW YOUR WORK and EXPLAIN YOUR STEPS.
Without that information, if you make a mistake, it is very difficult
to see where you went wrong and award proper partial credit. Wrong
answers with no explanations will get zero points.
- If you are absolutely stuck on a calculation and don’t know
how to finish (or even start), if you can at least make a qualitative
estimate for what you expect the answer to be, and why, that can help
with partial points.
- Make sure to always have units attached to your numbers.