COSMOLOGY & HUBBLE EXPANSION, DARK MATTER, LENSING 
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Cosmology
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Which of the following observations about the nature of the
universe can be made without using any special equipment?
    a) The universe is expanding.
    b) Most of the matter in the universe does not emit light.
   $c) Luminous matter in the universe occurs in clumps rather than being
       evenly distributed.
    d) There is background radiation from the Big Bang.

The cosmological principle enables astronomers to generalize
from what they observe in the nearby universe to the properties of 
the universe as a whole.  The principle means that no matter where you 
are in space, you should see that 
    a) galaxies are all moving away from a center.
    b) the universe does not change with time.
   $c) on average, space looks the same in all directions.
    d) every region of space is unique.

Your job is to compile a representative catalog of galaxies.  Assuming
our region of the Universe is typical, the best criterion to use to
decide whether to include galaxies in the catalog is to include all
galaxies on the sky with 
    a) magnitudes brighter than some chosen limit.
    b) apparent diameters larger than some chosen limit.
   $c) recession velocities less than a certain (large) amount.   
    d) recession velocities less than a certain (small) amount.   

Suppose the Universe were not expanding, but was in some kind of steady
state.  How should galaxy recession velocities correlate with
distance?  They should
    a) be directly proportional to distance.
    b) reverse the trend we see today and correlate inversely with distance.
    c) show a scatter plot with most recession velocities positive.
   $d) show a scatter plot with equal numbers of positive and negative
       recession velocities.

The night sky is relatively dark because
      a) the Earth's atmosphere obscures most of the light.
      b) the universe is mostly empty.
     $c) the Big Bang happened about 15 billion years ago.
      d) the universe is very large and old.

We only observe events that happened in the past because
    a) It takes time to reduce the data.
   $b) the speed of light is finite.
    c) the universe is very old.
    d) none of the above; we often observe events that happen at the
same time as the observation.

The blueshift exhibited by some nearby external galaxies lends support to the 
    a) Big Bang model, because those galaxies are expanding towards us.
   $b) Local Group concept, because nearby galaxies interact gravitationally.
    c) evolution theory, because galaxies change color as they evolve.
    d) oscillating universe theory, because some galaxies are moving
together already.
                                      
Suppose you've accepted that the universe is expanding, and will
always expand.  You must then accept that 
   a) there is either no center to the universe, or we are at the center.
   b) the universe is a one-shot deal.
   c) either the average distance between galaxies always grows,
      or the distance between stars in the galaxies grows.
  $d) either the density of the universe always decreases or new matter must be
continuously created. 

The Steady State theory of cosmology holds that the universe is expanding,
but new matter is created so that the appearance of the universe does
not change.  This theory would imply that
   a) there are other galaxies in the universe that are several  
      times as old as our own Milky Way.
   b) there was no Big Bang, and therefore there is no 3K cosmic background
      radiation today.
   c) the space density of quasars should look the same at
      all redshifts.
  $d) all of the above.

The observed redshifts of galaxies mean that
   a)  our Galaxy is at the center of an expanding universe
   b)  gravity can never overcome the expansion left over from the Big Bang
  $c)  photons' wavelengths get stretched as they travel towards us
   d)  galaxies are growing smaller

If the speed of expansion of the Universe is increasing, then 
redshift-based estimates of the look-back time to distant galaxies
based on a steady expansion rate have been 
    a) too small
   $b) too large
    c) just fine

If the universe is expanding, won't the solar system eventually expand apart?
    a)  The solar system may actually be shrinking now, which makes
the Universe LOOK like it's expanding.  
   $b)  No, its gravity holds it together.
    c)  No, because there is no planetary redshift. 
    d)  Eventually, but only after a very long time.

Suppose that every object in the universe was created simultaneously, 15
billion years ago.  Which of the following statements is true of 
an object that is 16 billion light years away?
    a) It shows that the universe has to be infinite.
    b) Its light first reached the Earth one billion years ago.
    c) We will never be able to see it.
   $d) We will not see it until one billion years from now.

Olber's paradox asks why the night sky is dark, when every line of
sight must eventually fall on a star. Which of the following reasons
would best explain the darkness at night?  It is because the universe is
   a) infinite and mostly empty.
   b) clumpy, so not every sightline intercepts a star. 
   c) expanding, so distant stars are red-shifted.
  $d) young, so there are only stars to a finite distance. 
   
The look-back time to an object is the number of years between when
the object emitted the light we see and the present.  What piece of
information surely does NOT affect the look-back time for a distant object?   
    a) its distance.
    b) the speed of light.
    c) the rate of expansion of the universe.
    d) the acceleration or deceleration of the universe.
   $e) none of the above.

Suppose the Hubble constant were measured and found to be twice as
large as it is now believed to be. The implied maximum age of the
universe in a Big Bang model would be 
  $a) halved
   b) the same
   c) doubled
   d) squared

The Hubble age of the universe, 1/H, represents how long ago the 
Big Bang happened, based on its current rate of expansion. Considering 
only the gravitational interaction of matter, the Hubble age must be
   $a) a maximum possible age
    b) a minimum possible age
    c) same as the actual age
    d) independent of the Hubble constant

If the Hubble constant, H, is larger at great distances, then the
   a) universe must be older than we suspect.
   b) matter in the universe is not important to its motion.
  $c) expansion is slowing.
   d) all of the above
   e) none of these
 
If the Big Bang cosmology is correct, then
   a) the most distant galaxies we observe are seen now as they will
      be in the future
  $b) nearby galaxies are seen at a more advanced stage of evolution
      than distant galaxies
   c) matter is being continually created
   d) the universal expansion must proceed at the same rate now as it 
      did when the microwave background was produced 

There must be some large distance (the Hubble length D=c/H) which is
too far away for light to have reached us during the age of the
Universe. The expansion velocity relative to us at that distance must be 
    a) zero
    b) infinite
    c) less than the speed of light
   $d) the speed of light or greater

The volume of a closed universe that stops expanding and eventually
recontracts is  
    a) finite.  Spacetime is infinite, but matter (stars and galaxies
       inhabit a bounded region.  
   $b) finite. Spacetime itself is bounded and has finite volume.
    c) infinite. Spacetime goes on forever and has infinite volume.
    d) infinite. Spacetime is bounded, but there is an infinite amount
       of matter within it. 

If the Big Bang theory is correct, and there is not enough mass to
close the universe, then  
    a) more Big Bangs will occur.
    b) there is no "dark matter".
   $c) the universe will eventually be entirely cold.
    d) the expansion will slow to a halt.

Lyman-alpha absorbers are dense clouds of neutral and ionized hydrogen 
believed to be the building blocks of normal galaxies. Their metallicities 
tend to be
    a)  larger the farther they are located away from us.
    b)  all about the same.
   $c)  smaller the farther they are located away from us.
    d)  zero, since they have only hydrogen.

Recent observations suggest that galaxies are found in large
sheets and filament-like structures, but that there are also enormous
holes and voids where no galaxies are found. This shows that the
universe probably
  $a)  has the largest, most massive structures where filaments join
   b)  formed stars, then galaxies, then clusters of galaxies
   c)  formed clusters of galaxies, then galaxies, then stars
   d)  inflated rapidly, producing spongelike structure

The cosmic background radiation provides strong evidence that
   a)  star formation has been taking place for billions of years
  $b)  the universe evolved from a hot, dense state
   c)  colliding galaxies release enormous amounts of synchrotron radiation
   d)  at 3deg Kelvin, the early universe was extremely cool

The cosmic background radiation is visible in every direction because
   a)  we are at the center of the universe
   b)  it is just now passing by us at the speed of light
  $c)  it pervades all space 
   d)  it has reflected in every direction over the age of the universe.


Dark Matter & Lensing
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What would be the best evidence for "missing mass" in the Milky Way?
   a)  density of stars in the spiral arms
  $b)  orbital speeds of gas clouds beyond the orbit of the Sun
   c)  orbital eccentricities of objects in the disk
   d)  chemical composition of globular cluster stars

The gravitational effect on light coming from a massive object is that
the light will
    a) be shifted to higher frequencies
   $b) have its spectrum shifted to the red
    c) show no effects from the gravitational field
    d) travel more slowly through space

Which change in appearance of a normal star will occur when a massive
dark object (a "MACHO") passes directly between you and the star.  
   a) There is no change since dark matter cannot affect light.
   b) The star light disappears momentarily behind the event horizon.
   c) The star dims because the MACHO blocks the light.
  $d) The star brightens temporarily because of gravitational microlensing.

Which of the following measurements can NOT be used to measure the amount
of dark matter in a cluster of galaxies?  
    a) The dispersion in the speeds of galaxies orbiting the cluster center.  
   $b) The average speed of galaxies orbiting the cluster center.  
    c) The deflection of light rays from a background object
passing by the outskirts of the cluster. 
    d) The properties of x-rays emitted by gas that has been heated by
falling into the cluster.  

A solar-mass black hole lies halfway between us and a solar-type
star, but not lined up exactly.  What do you predict we see when you
observe the star?                                             
    a) Bright light from the black hole would outshine the star
    b) Nothing; the star light would all go down the black hole
    c) 1 image of the star, somewhat fainter than the original
   $d) 2 images of the star, one on each side of the black hole