Read Chapter 20
1.) List 3 ways in which elliptical galaxies differ from
spiral galaxies.
2.) Describe irregular galaxies.
3.) How are galaxies distributed throughout the universe:
a.) Galaxies tend to be evenly spread throughout the universe
b.) Galaxies tend to reside near each other in groups or
clusters; these groupings are scattered
throughout the universe
c.) Most of the galaxies in the universe reside near each other in
a single large grouping; the
remaining galaxies are sparsely scattered throughout the universe
d.) None of the above
4.) "Main Sequence Fitting":
a.) Can be used to measure distance
b.) Compares the apparent brightness of one cluster of stars to that of
another
c.) Usually requires plotting measurements on
a Hertzsprung-Russell (H-R) diagram
d.) All of the above
e.) None of the above
5.) The "Tully-Fisher" Relation
a.) Says that a galaxy's rotation speed is proportional to its
luminosity
b.) Can be used to find the apparent brightness of
elliptical galaxies
c.) Can only be applied accurately for galaxies within about
10,000 lightyears
d.) All of the above
e.) None of the above
6.)
a.)
What does the term "standard candle" mean in astronomy?
b.)
Write 2 or 3 sentences that explain why white dwarf supernovae
are good standard candles.
7.) (problem adapted from the textbook)
Using modern telescopes, we can see some of the
Cepheid variable stars in the galaxy M100.
Astronomers measured the apparent brightness of
one of the Cepheid variable stars; it is
3.8 x 10-19 watt/m2. From
the period and the
period-luminosity relationship, they calculated that the
luminosity is 1.2 x 1030 watts.
Use the apparent brightness vs luminosity formula
(it is presented in "Mathematical Insight 20.1")
to calculate the distance between the Earth and
the Cepheid variable star in M100 (i.e. the
distance between the Earth and M100).
8.) As we look at galaxies at further and further distances,
and ignoring the "noise" caused by random
motion, we find that:
a.) The more distant a galaxy is, the larger it looks to us
b.) The more distant a galaxy is, the bluer its light looks to us
c.) The more distant a galaxy is, the faster it is moving away from us
d.) All of the above
e.) None of the above
9.)
a.) Write the equation for Hubble's Law.
b.) Suppose that you lived in a different group of galaxies than our
own and suppose that you
observed other groups of galaxies.
Do you think that they would be stationary or moving
relative to your galaxy?
c.) -- if they are moving, which way would they be moving (toward or
away)?
or, if they are stationary, why are they stationary?
10.) If you lived in a galaxy far, far away, and your civilization
were able to make the same types of observations
and calculations that
humans have made, (ignoring the "noise" caused by random motions)
you would think that
a.) Other galaxies are moving away from you at a speed proportional to
their distance from you
b.) Other galaxies are moving toward you at a speed proportional to their
distance from Earth
c.) The galaxies between you and Earth are moving toward you and the
galaxies on the far side
of you or Earth are moving away from you
d.) None of the above
11.)
What is a "cosmological redshift"?
12.) Which one of the following is true?
a.) The age of the universe is approximately equal to Ho
b.) The age of the universe is approximately equal to Ho2
c.) The age of the universe is approximately equal to 1/Ho
d.) The age of the universe is approximately equal to 1/(Ho2)