PHYS 107 ASTRONOMY 9

• Question 1

  1 out of 1 points

  	Compared to stars like the Sun, B stars like RigeL have:
  	Selected Answer:   lifetimes much shorter than the Sun Correct Answer:  lifetimes much shorter than the Sun Response Feedback: Correct, hot, luminous massive stars like Rigel burn through there fuel much more quickly and thus have lifetimes much shorter than the Sun.

• Question 2

  1 out of 1 points

  	What elements do astronomers consider metals or heavy elements?
  	Selected Answer:    all elements besides hydrogen and helium Correct Answer:    all elements besides hydrogen and helium Response Feedback:  Correct, all elements but hydrogen and helium are called metals or heavy elements

• Question 3

  1 out of 1 points

  	The best evidence for dark matter in the Milky Way is:
  	Selected Answer:   the higher than expected orbital velocities of stars and gas clouds at the outskirts of the galaxy Correct Answer:  the higher than expected orbital velocities of stars and gas clouds at the outskirts of the galaxy Response Feedback: Correct, there appears to be more mass in the galaxy than can be accounted for by the number of stars and gas clouds.

• Question 4

  1 out of 1 points

  	Harlow Shapley concluded that the Sun was not located at the center of the Milky Way Galaxy by
  	Selected Answer:    mapping the distribution of globular clusters in the galaxy. Correct Answer:    mapping the distribution of globular clusters in the galaxy. Response Feedback:  Correct, he used globular clusters in the halo of the Galaxy away from the absorption of dust in the plane to determine the shape

• Question 5

  1 out of 1 points

  	We infer a high mass black hole exists in the center of the Milky Way because:
  	Selected Answer:   we can watch the orbits of stars in the center and use Kepler's Third Law Correct Answer:  we can watch the orbits of stars in the center and use Kepler's Third Law Response Feedback: Correct, by tracking the orbits of stars in the core of the Milky Way we can apply Kepler's Third Law to determine the central mass, since it is very massive (1,000,000 Solar masses) but located within a region ~1 AU across it must be a black hole.

• Question 6

  1 out of 1 points

  	Suppose that the calibration of the Cephiod period-luminosity relationship was uncertain and resulted in distances uncertain by 30% in the Milky Way.  What would we see in the uncertainties in distances to Cephieds in other galaxies:
  	Selected Answer:   the uncertainty in distance would be at least 30% Correct Answer:  the uncertainty in distance would be at least 30% Response Feedback: Correct, any uncertainty in the calibration of nearby objects results in at least that uncertainty in more distant objects.

• Question 7

  1 out of 1 points

  	Choose the best evidence that the disk of the Milky Way does not rotate like a solid wheel:
  	Selected Answer:   stars in the disk have a similar velocity around the center (flat rotation curve) Correct Answer:  stars in the disk have a similar velocity around the center (flat rotation curve) Response Feedback: Correct, while the velocities are the same since the distances increase the periods must increase as you go out.  A flat disk has the periods stay the same throughout the disk and the velocities increase as you go out.

• Question 8

  1 out of 1 points

  	If we see a high mass Ostar in the Andromeda galaxy tonight, we know that:
  	Selected Answer:   it will have already gone (Type II) supernova Correct Answer:  it will have already gone (Type II) supernova Response Feedback: Correct, remember that an O star has lifetime of order 1 million years, and so even before the light from an O star reaches us from Andromeda (2 million light years away) the star has been born, evolved, and exploded as a Type II SN before any being in the MIlky Way can see it.

• Question 9

  0 out of 1 points

  	Suppose the Hubble constant turned out to be 142 km/sec/mpc and not 71 km/sec/mpc. How would that affect our estimate of the age of the Universe?
  	Selected Answer:   The Universe would be about 30 billion yrs old. Correct Answer:  The Universe would be about 7 billion yrs old.

• Question 10

  1 out of 1 points

  	When we look at the Galactic center we see the stars as they were:
  	Selected Answer:   25,000 years ago Correct Answer:  25,000 years ago Response Feedback: Correct, 25,000 light years means that light takes 25,000 years to reach us.

• Question 11

  1 out of 1 points

  	What is the diameter of the disk of the Milky Way?
  	Selected Answer:   100,000 light years Correct Answer:   100,000 light years

• Question 12

  1 out of 1 points

  	What makes up the interstellar medium?
  	Selected Answer:   gas and dust  Correct Answer:  gas and dust  Response Feedback:  Correct, it is the gas and dust out of which new stars and planets form

• Question 13

  1 out of 1 points

  	Why are Cepheid variables important?
  	Selected Answer:    Cepheids variables are pulsating stars whose pulsation periods are directly related to their true luminosities. Therefore they can be used as distance indicators. Correct Answer:    Cepheids variables are pulsating stars whose pulsation periods are directly related to their true luminosities. Therefore they can be used as distance indicators. Response Feedback:  Correct, they a pulsating stars whose periods are related to their luminosities

• Question 14

  1 out of 1 points

  	We can determine the age of a globular cluster by:
  	Selected Answer:   finding the spectral types of the most luminous main sequence stars. Correct Answer:  finding the spectral types of the most luminous main sequence stars. Response Feedback: Correct, the most massive/luminous main sequence stars left are the ones whose lifetime is less than the age of the cluster, so the cluster must be just older than that age. All of the stars with lifetimes less than the age of the cluster will have evolved off the main sequence already.

• Question 15

  1 out of 1 points

  	The Sun's location in the Milky Way is:
  	Selected Answer:   in the disk about 2/3rds the way out from the center Correct Answer:  in the disk about 2/3rds the way out from the center Response Feedback: Correct, we are about 25,000 light years from the center, and the Milky Way is approximately 40-50,000 light years in radius.

• Question 16

  1 out of 1 points

  	An OB-star like Rigel moving through the Milky Way disk is a:
  	Selected Answer:   Population I star Correct Answer:  Population I star Response Feedback: Correct, "population I" refers to stars in the disk, "population II" to stars in the halo (the oldest stars we currently see), and "population III to the stars that must have formed first to provide the elements ("metals") we see in the halo stars.

• Question 17

  1 out of 1 points

  	Compared to stars in the disk like the Sun, stars in the halo of the galaxy formed:
  	Selected Answer:   earlier, out of material less enriched in heavy elements Correct Answer:  earlier, out of material less enriched in heavy elements Response Feedback: Correct, the halo stars formed before the majority of the supernovae went off to enrich subsequent generations of stars like the Sun.

• Question 18

  1 out of 1 points

  	The Milky Way is:
  	Selected Answer:   the name of our Galaxy Correct Answer:  the name of our Galaxy Response Feedback: Correct, that is the name given to our galaxy drawn from Greek mythology.

• Question 19

  1 out of 1 points

  	Where are most heavy elements made?
  	Selected Answer:    In stars and supernovae Correct Answer:    In stars and supernovae Response Feedback:  Correct, the elements heavier than hydrogen and helium were made in stars and in the deaths (supernovae) of stars

• Question 20

  1 out of 1 points

  	Clusters of stars are:
  	Selected Answer:   bound together by gravity Correct Answer:  bound together by gravity Response Feedback: Correct, when we see stars that we can identify as being a cluster, that means they are bound together by the force of gravity and move through the galaxy together.