Astr 222 Practice Midterm #1
questions similar in style to the ones below
Each question is worth 5 points.
Your answer should be a a few sentences / short paragraph long
- Describe what is meant by Population I
objects and Population II objects. Give examples.
- Describe the Magallenic Clouds.
- Why do we believe there is a lot of dark
matter in the galaxy?
- 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
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.
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
- 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 Magellanic Cloud?
- Describe the Oort Limit and sketch the
rotation curve of the Milky Way. Explain how the rotation
curve shows that there is dark matter in our Galaxy. Using
those two arguments alone (Oort Limit and rotation curve),
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
- 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.
- Imagine a galaxy forms from a single burst of
star formation, after which time all star formation stops.
Describe how the galaxy's luminosity, B-V color, and stellar
mass-to-light ratio changes over time. Be sure to explain
physically why these changes are happening, and also give some
characteristic timescales for the changes. Again, a sketch
- Describe three arguments that support the idea
that there is a supermassive black hole in the nucleus of the
Milky Way. How massive is this black hole?
- The Large Magellanic Cloud (LMC) orbits around
the Milky Way, at a current distance of about 50 kpc. Explain
what will happen to the LMC over the course of billions of
years as it continues orbiting around the Galaxy. Make sure to
describe the physical processes involved!
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 = -2.5log10(f1/f2)
- 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. Arguments and explanations you
make in your answers must be based on material covered in
class or on HW sets.
- 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 top").
- 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
- 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.