PHYS 107 ASTRONOMY 7

• Question 1

  1 out of 1 points

  	Evolving stars always move in the HR-diagram (plot of luminosity versus temperature):
  	Selected Answer:   none of the above, stars move to different portions of the diagram depending on their evolutionary phase Correct Answer:  none of the above, stars move to different portions of the diagram depending on their evolutionary phase Response Feedback: Correct, consider for example the evolution of the Sun, first it becomes a brighter and cooler red giant, and then becomes a fainter and hotter white dwarf (and moves through other portions of the HR-diagram as well).  Remember the results of the evolution demonstration, stars can "move" both toward hotter and cooler temperatures, and toward brighter and fainter luminosities.

• Question 2

  1 out of 1 points

  	The eventual fate of a star like the Sun is to become a:
  	Selected Answer:   white dwarf Correct Answer:  white dwarf Response Feedback: Correct, the Sun will eventually become a white dwarf after it has exhausted the fuel in its core.

• Question 3

  0 out of 1 points

  	A G2V star and a K2V star have the same:
  	Selected Answer:   luminosity Correct Answer:  none of the above Response Feedback: Incorrect, remember for main sequence stars the mass, radius, luminosity and temperature are all related (and all are lower as you get to later spectral types).

• Question 4

  1 out of 1 points

  	If the Sun were to suddenly expand to be 10 times its current size of ~0.0047 AU but keep the same mass, the Earth would:
  	Selected Answer:   stay in the same orbit Correct Answer:  stay in the same orbit Response Feedback: Correct, the force on the Earth would be unchanged since the mass of the Sun is unchanged, so the orbit would not change. Note this would not be true if the Sun were to expand to be larger than the Earth's orbit of course. Also note that orbital distances are defined from both object's centers, so while the Earth in some sense is "closer" to the Sun's surface, its distance from the Sun's center and hence its orbital distance is unchanged.

• Question 5

  1 out of 1 points

  	Which of the following is the phase of matter in the Sun?
  	Selected Answer:    plasma Correct Answer:    plasma Response Feedback:  Correct, essentially all of the material in the Sun is ionized

• Question 6

  1 out of 1 points

  	The sequence OBAFGKM is a sequence of:
  	Selected Answer:   decreasing temperature Correct Answer:  decreasing temperature Response Feedback: Correct, the OBAFGKM refers to the surface temperature; remember a M supergiant (cool) can be as bright as an O main sequence star (hot), think Beteguese and Rigel

• Question 7

  1 out of 1 points

  	The eventual fate of a star like the Sun is to become a:
  	Selected Answer:   white dwarf Correct Answer:  white dwarf Response Feedback: Correct, the Sun will eventually become a white dwarf after it has exhausted the fuel in its core.

• Question 8

  1 out of 1 points

  	Based on its surface temperature of ~5,800 K, most photons that leave the Sun's surface lie in which region of the electromagnetic spectrum?
  	Selected Answer:    Visible Correct Answer:    Visible Response Feedback:  Correct, remember Wein's Law

• Question 9

  1 out of 1 points

  	The force of gravity acts to:
  	Selected Answer:   make a star smaller Correct Answer:  make a star smaller Response Feedback: Correct, the lifetime of a star is spent fusing elements to counteract the force of gravity which is trying to make the star collapse.

• Question 10

  1 out of 1 points

  	Compared to the variations in luminosity between stars, the magnitude of the variations in mass between stars are:
  	Selected Answer:   much smaller Correct Answer:  much smaller Response Feedback: Correct, the variations in luminosity are approximately a factor of 100,000,000 while masses vary between about 0.1 and 100 Solar masses (a factor of 1,000).