Quiz 3

i) Attempt all questions in Part A and 1 of the questions in Part B. Please write all answers to Part A on these sheets; extra paper is available if needed.

ii) With few exceptions, Part B questions call for a paragraph of coherent English. Points will be deducted if sentences are incomplete and reduced to a list of items or a phrase or two. Do not, however, pad your answer by rewriting the question, by rewriting one sentence in several different ways, etc. Answers to Part B must be written on a blank sheet and not crammed into crevices on these sheets.

Time allowed is 75 minutes. All work must be your own!

Part A

Part B

B1.	a.	Explain why the Hubble Space Telescope is able to use Cepheid variables to measure distances to galaxies much more distant than those measurable from Cepheids using much larger telescopes on the ground.
	b.	Explain clearly what is meant by 'the period-luminosity relation' of Cepheid variables, and show why it is so useful as a tool for measuring distances to spiral galaxies.
	c.	The following is a period-luminosity relation (it is not the relation for Cepheids):   Discuss whether this relation would permit the variable stars obeying it to be used for distance measurements?
B2.	a.	What is a neutron star? Your description should include remarks on the mass, size, composition, temperature, and any other pertinent properties. Do not describe how a neutron star is formed.
	b.	What is a black hole? Your description should include remarks on the mass, size, composition, temperature, and any other pertinent properties. Do not describe how a black hole is formed
	c.	Describe how black holes are detected in our Galaxy. Be sure that your description is consistent with the fact that light cannot escape from a black hole. Also explain why the observations you describe point to a black hole rather than a neutron star or a white dwarf.
B3.	a.	Describe the difference between Population I and Population II stars in terms of the following properties: - metal content (relative to solar value) - age - mass of the most luminous stars - motion in the Galaxy Be as specific as possible: i.e., 'about 500 billion years' not simply 'very, very old'!
	b.	Discuss how two of the above differences are to be understood in terms of a model for the formation of the Galaxy.
B4.	a.	What is Hubble's Law?
	b.	Explain how Hubble's Law, V=H0r, is established from observations of galaxies. You are expected to discuss how the radial velocities V and the distances r are measured.
		All galaxies are receding from us. Does Hubble's Law then imply that our Galaxy is in a special position from which all other galaxies are fleeing? Discuss your choice of "yes" or "no".
B5.	a.	What is the zone of avoidance? If we lived in an elliptical galaxy, would we see a zone of avoidance?
	b.	If a star appears red, what observations would you make to decide if it is - a cool star, or -a hot star reddened by interstellar dust, or -a hot star reddened by the Doppler shift arising from very rapid motion away from us?
	c.	Why does the setting sun appear redder than the noonday sun?
B6.	a.	Describe Hubble's scheme for the classification of galaxies, E, S, SB. Include a discussion of the difference between E0 and E7 galaxies, and Sa, Sb, and Sc galaxies.
	b.	Why is Hubble's 'tuning fork' diagram not thought to be an evolutionary sequence for galaxies?
B7.	a.	What is the difference between the cosmological principle and the perfect cosmological principle?
	b.	What is a fundamental difference between model universes built upon the cosmological principle and those built upon the perfect cosmological principle?
	c.	Explain clearly why the age of an expanding evolutionary universe is inversely proportional to the Hubble constant H0, i.e., t 1/H0.