Download Answers - Physics

Astronomy A105 Midterm 2
Spring 2007
______________________________________ Name
Multiple Choice (3 points each):
Please circle your answers as they will be your only record of the answers you have given
on the test. Please then mark the answer in the appropriate bubble on the scan sheet. Be
sure to include your name. Use only a #2 pencil. If your pencil breaks, or you do not
have one, a pencil will be provided at the front of the room. There are 25 multiple choice
questions.
1) When we examine the rotation curve (shown above) for our galaxy we notice that the
orbital velocities increase as you go to the outmost parts of our galaxy. From that fact,
we know that 90% of our galaxy’s mass is in what form?
• A) Hydrogen
• B) stars
• C) dust
• D) dark matter
2) How long does it take our sun to orbit our galaxy?
• A) 25 million years
• B) 250 million years
• C) 2.5 billion years
• D) our sun does not orbit our galaxy
3) What type of galaxy do we live in?
• A) unbarred spiral
• B) barred spiral
• C) elliptical
• D) irregular
4) What is a bubble?
• A) a region of space with less gas
• B) a region of space with more gas
• C) another term for a star forming region
• D) a region that is completely empty
5) If a bubble breaks through the disc of our galaxy what happens?
• A) the bubble stops expanding
• B) a pressure blow out
• C) the bubble becomes a star forming region
• D) the bubble forms a spiral arm
6) What determines the volume of space that a hot phase region can expand into?
• A) velocity of the hot phase
• B) temperature of the hot phase
• C) pressure of the hot phase
• D) Trick! The hot phase contracts.
7) The B-V value of the sun is 0.68 as viewed from earth. What is the B-V value for the
sun from Jupiter (5 times further away from the sun than the earth)?
• A) 0.68
• B) 3.4
• C) 5.68
• D) 17
8) The B-V value of the sun is 0.68 as viewed from earth. What would the V value for
the sun be if it were in the Pleiades cluster as diagramed above?
• A) V = 5
• B) V = 8
• C) V = 11 (corrected)
• D) V = 16
9) What determines the resolution of a telescope?
• A) diameter (this was from a homework last year)
• B) light collected
• C) magnification
• D) all of these
10) If a neutron star accretes matter from a companion star, how does the spin change?
• A) spins faster
• B) spins slower
• C) spin unchanged
• D) stops spinning
11) What are pulsars?
• A) rapidly spinning neutron stars
• B) rapidly spinning black holes
• C) stars that change temperature rapidly
• D) stars that change size rapidly
12) Where does the energy that pulsars emit come from?
• A) heat
• B) fusion
• C) gravity
• D) spin
13) If we know a star’s apparent and absolute brightnesses (or magnitudes) then what
value can we calculate?
• A) age of the star
• B) distance to the star
• C) temperature of the star
• D) we can calculate all of these
14) Absolute Magnitude is a measure of:
• A) a star’s brightness as viewed from the earth
• B) a star’s brightness as viewed from 93 million miles away
• C) a star’s brightness as viewed from 10 parsecs away
• D) the temperature of a star
15) Apparent Magnitude is a measure of:
• A) a star’s brightness as viewed from the earth
• B) a star’s brightness as viewed from 93 million miles away
• C) a star’s brightness as viewed from 10 parsecs away
• D) the temperature of a star
16) Which of the following does NOT affect how much energy an object radiates?
• A) radius of the object
• B) temperature of the object
• C) distance to the object
• D) all of these affect how much energy the object radiates
17) What is NOT true of stars in a cluster?
• A) they are about the same distance away
• B) they are about the same age
• C) they are about the same mass
• D) all of these are true
18) How do we find the distance to a cluster?
• A) by finding the color of the turn off point
• B) by finding the brightness of the turn off point
• C) by finding the color of the sun if it were in the cluster and comparing that to its
actual color
• D) by finding the brightness of the sun if it were in the cluster and comparing
that to its actual brightness
19) What is the best way to find the age of a cluster?
• A) by finding the color of the turn off point
• B) by finding the brightness of the turn off point
• C) by finding the color of the sun if it were in the cluster and comparing that to its
actual color
• D) by finding the brightness of the sun if it were in the cluster and comparing that
to its actual brightness
The diagram above will be used for questions 20 and 21.
20) For the HR diagram shown, if stars A and B are the same distance from earth which
has a higher temperature (ignore absorption)?
• A) A
• B) B
• C) they have the same temperature
• D) you cannot tell from this diagram
21) For the HR diagram shown, if stars A and B are the same distance from earth which
is brighter (ignore absorption)?
• A) A
• B) B
• C) they have the same brightness
• D) you cannot tell from this diagram
22) Where do you normally find spiral galaxies?
• A) in the cores of giant galaxy clusters
• B) on their own with a few satellite galaxies
• C) in orbit around a larger galaxy
• D) everywhere
23) Where are you most likely to find giant elliptical galaxies?
• A) in the cores of giant galaxy clusters
• B) on their own with a few satellite galaxies
• C) in orbit around a larger galaxy
• D) everywhere
24) What type of galaxy do the smallest galaxies fall under?
• A) spiral galaxies
• B) elliptical galaxies
• C) irregular galaxies
• D) all galaxy types are the same size
25) What type of galaxy do the largest galaxies fall under?
• A) spiral galaxies
• B) elliptical galaxies
• C) irregular galaxies
• D) all galaxy types are the same size
SHORT ANSWER QUESTIONS:
Each question is worth 15 points. Be sure to answer all parts of all questions fully (I
can’t give points if you don’t answer). Please note that there are 5 short answer
questions! Please do all 5.
1) What are the 3 components of our galaxy? Which parts of our galaxy do you find
Population I stars? Which parts do you find Population II stars? What are the differences
between Population I and Population II stars?
Bulge, Disc, Halo
Pop I found in Bulge and Disc
Pop II found in Halo
Pop I stars are younger and have more metals than Pop II stars
2) What are the 3 phases of the Interstellar Medium (ISM)? Rank the phases by
temperature and by density (specify which are highest and lowest). How does each phase
play a role in the “circle of life”?
Cold, Warm, Hot
Density: Lowest is Hot, then Warm, then Cold is densest.
Tempt: Hot is hottest, then Warm, then Cold is coldest (have to give you some easy
points)
For the circle of life the gas starts at the Hot phase after the death of a massive star.
That gas slowly cools with time until it is the warm phase, and then cools further
until it becomes the cold phase where it forms into a giant molecular cloud. Stars
are then formed from the cold phase to begin the cycle anew.
3) Why is it difficult to observe the center of our galaxy in the optical? What type of
light is the best type of light to use to observe the center of our galaxy? Why is this type
of light the best?
The center of our galaxy is blocked by dust in the optical (the dust absorbs almost
all the light).
The best type of light to use is radio because radio waves are bigger than dust
particles. Therefore the dust does not absorb radio waves.
4) For the above image circle the globular cluster. How did you know that was the
globular cluster (even if you guess why did you guess that – what about it said to you that
it might be the globular cluster)? What are the dark spots on the image?
I will leave it to you to find the globular. The dark spots are giant molecular clouds
that are much closer to use than the globular cluster.
5) For the image above circle the 3 star groups. For each cluster label them as either
globular cluster, open cluster, or galaxy. If it is a galaxy, what type of galaxy is it? What
do the colors of the star groups tell you about each group (name 2 things – but they sort
of relate to each other – i.e. what does the first thing also tell you?)? BONUS: What are
the names of the star groups (i.e. if galaxy – name of galaxy, if star cluster, name of star
cluster)?
The two yellow regions are globular clusters. The large blue cloudy area on the
bottom left is an irregular galaxy (Small Meganallic Clouds)