Astronomy 122 - Final Exam  answers



1.	Binary stars, mutually bound to each other by gravitational forces, allow us to  	
	derive which important stellar parameter?

		e.	stellar mass

2.	To determine the Sun's luminosity, we must know

		d.	the distance from the earth to the Sun.

3. 	The best shape for the cross-section of a large astronomical mirror in order to 	
	produce the sharpest images of very distant objects is

		d.	a parabolically shaped surface.

4. 	Chromatic aberration occurs in a telescope when

		b.	light of different colors focus to different points.

5. 	Refracting telescopes are limited because

		c.	lenses bend different colors of light different amounts.
		
6.	The pre main-sequence path on the H-R diagram of a protostar depends primarily on

		b.	its mass.

7.	A star that emits a planetary nebula is likely to

		c.	become a white dwarf.

8.	Compared with slowly rotating stars, the fastest spinning stars' absorption lines are 

		b.	broad and fuzzy.

9.	How is a parsec defined?

		b.	the distance which has a 1 arcsecond parallax.

10.	The resolution of a typical radio astronomy telescope for 1 meter wavelength is about

		c.	10,000 arc-seconds.

11.	Which of the following effective reactions is called the CNO cycle?
	
		b.	C + 4 H -> C + He + energy

12.	The radius of a white dwarf star is comparable to that of 

		d.	the Earth.

13.	A reflection nebula

		b.	is bluish in color.

14.	What is the approximate density of atoms in the interstellar medium?

		d.	1 atom/cm3

15.	Compared to the mass contained by the stars of the galaxy,

		b.	the interstellar medium contains about as much mass as the stars.

16.	What is the approximate density of dust in the interstellar medium?
		
		b.	1000 particles/km3

17.	What is the radius of the Sun?

		c.	700,000 kilometers

18.	Where is it most likely to find a white dwarf star?

		a.	Within a globular cluster

19.	What is located at the center of the Crab Nebula?

		a.  	a neutron star

20.	What is the maximum mass that supports matter against collapse to a black hole?

		d.	about 3 solar mass

21.	What appears at a distance to happen to time at the event horizon of a black hole?

		a.	Time stops

22.	The sun will eventually become

		e.	a white dwarf.

23.	The spin-flip of an electron in hydrogen results in

		e.	21-cm radio emission.

24.	What do astronomers call ionized hydrogen?
 
		e.	HII    

25.	Interstellar reddening refers to 

		a.	preferential dimming of short-wavelengths by dust

26.	What is the approximate value for the Schwarzschild radius for one solar mass?
	
		b.	3 kilometers

27.	 What is the escape velocity at the event horizon of a black hole?

		a.	the speed of light

28.	What model of a pulsar explains its observed properties?

		c.	the light-house model

29.	What type of star is associated with a pulsar?
	
		e.	a neutron star

30.	The path drawn on the H-R diagram below represents the change in

		b.	a Sun-like star during the "birth" of the star.

31.	What is the typical frequency of the pulses from a pulsar?

		b.	10 - 1000 per second

32.	Which of the following is NOT a property of a neutron star?

	--->	a.	cool surface
		b.	extremely high density
		c.	rapid rotation
		d.	size much smaller than a main-sequence star
		e.	strong magnetic field

33.	OB associations are marked by

		e.	new star formation.

34.	Emission nebulae are caused by

		a.	hot O- and B-type stars heating their surroundings.

35.	Differential rotation of the Sun refers to

		d.	The rapid speed of the rotation of the equator of the Sun.	

36.	Which of the following spectral types of stars has the longest main-sequence 
	lifetime?

	--->	a.	G
		b.	B
		c.	F
		d.	A
		e.	L

37.	Hawking Radiation refers to

		d.	evaporation of black holes.

38.	What object is suspected to be a black hole?

		e.	Cygnus X-1

39.	When two neutron stars coalesce, they are expected to emit

		b.	gravity waves (or gravitational radiation)

40.	Where are supermassive black holes thought to reside?

		d.	at the center of many galaxies

41.	A star's luminosity class is determined from

		a.	the width of its absorption lines

42.	How is the age of a globular cluster determined?

		e.	From the turnoff point on the H-R diagram

43.	Compared to a research quality vacuum on Earth, the density of interstellar 
 	gas medium is

		a.	the interstellar medium is much less dense.

44.	Molecular emission lines result from

		a.	electron orbital changes.
		b.	changes in the vibrational state of the molecule.
		c.	changes in the rotational state of the molecule.
	--->	d.	all of the above.
		e.	none of the above.

45.	A photon of light is absorbed by an atom
		
		c.	when an electron rises from an energy state to a higher energy state.

46.	A photon of wavelength 10 um is considered

		e.	infrared radiation.

47.	Different elements can be distinguished by their emission spectrum in that

		e.	they each produce different specific emission line wavelengths.

48.	The width of an emission line can be broadened through

		a.	thermal broadening.
		b.	rotational broadening.
		c.	collisional broadening.
	--->	d.	all of the above.
		e.	none of the above.

49.	The temperature of a star can be inferred from

		a.	the peak of the continuous spectrum of the star.
		b.	the width of the absorption lines in the star's spectrum.
		c.	the specific lines that are present in the star's absorption 
			spectrum.
	--->	d.	all of the above.
		e.	none of the above.

50.	The peak wavelength in the spectrum of light from a star can be used to determine its

		a.	radial velocity.
		b.	absolute age.
	-->	c.	surface temperature.
		d.	distance from Earth.
		e.	all of the above.

51.	What type of radiation has wavelengths greater than 100 microns?

		d.	radio waves

52.	What type of radiation has wavelengths in the range of 0.7 microns to 100 microns?

		a.	visible light
		b.	gamma-rays
		c.	X-rays
		d.	radio waves
	--->	e.	none of the above

53.	Star A appears to have the same brightness through a red and blue filter.  Star B appears 
	brighter in the blue than in the red.  Star C appears brighter in the red than in the blue.  
	Rank these stars in order of increasing temperature.

		a.	C, A, B

54.	Light with a wavelength of 600 nm (or 0.6 microns) is perceived to be

		a.	red.

55.	What is the approximate energy carried by a photon of visible light?

		a.	4 x 10-19 Joules

56.	Most of the energy of a supernova explosion is carried away by

		b.	neutrinos.

57. 	Which class of stars is the oldest?

		c.	stars with less abundance of heavy elements

58. 	White dwarf stars without binary companions have the following characteristics

		b.	have ceased to produce thermonuclear energy, and are cooling.

59.	The Helium atom is composed of

		d. 	two electrons and a nucleus of two protons and two neutrons.

60.	Choose the correct order of electromagnetic radiations, from shortest to 
	longest wavelength

		c.	UV, visible, IR, radio

61. 	Compared with the 100-inch diameter Mount Wilson telescope, the 200-inch diameter 	
	Mount Palomar telescope has a greater light-gathering power, by a factor of

		c.	4	

62. 	Star A is magnitude 6 and Star B is magnitude 1

		c.	Star B is 100 times brighter than Star A	

63.	Stars on the main-sequence are

		b.	generating energy by thermonuclear fusion in their cores.

64.	What is the approximate expected main-sequence lifetime of a 15 solar mass star?

		e.	about 15 million years

65.	Which of the following statements about the rate of stellar evolution is true?

		e.	the more massive the original star, the faster the evolution.

66.	Which type of radiation could provide the best resolution in the same 
	size instrument?

		a.	radio waves 
		b.	infrared radiation 
		c.	sound waves                  
	--->	d.	visible light 
		e.	They're all about the same

67.	Atoms in a hot gas emit a spectrum, which is

		d.	a series of specific colors ("lines"), unique to the type of atom.

68.	Which of the following spectral types of stars has the shortest main-sequence
 	lifetime?

		c.	O

69.	The relationship between mass and luminosity of stars on the main-sequence is that

		b.	the greater the stellar mass, the larger the luminosity.

70. 	As a new star evolves from cool dust and gas to a hot star, its peak spectral 
	wavelength 

		b.	changes from the infrared to the visible wavelengths.

71.	We understand that stars above the main-sequence on the H-R diagram are:

		c.	stars with larger surface areas.

72.	The major source of energy in the pre-main-sequence life of the Sun was

		c.	gravitational.

73.	Infrared stars within the Orion Nebula are examples of which stage of stellar 
	evolution?

		b.	protostar and young star 

74. 	A supernova explosion 

		a.	produces heavy nuclei all the way up to uranium and thorium.

75.	Which type of Supernova would typically occur soonest after the birth of a star?

		b.	type II

76.	A white-dwarf is the likely end result of which type of the following main-sequence 	
	stars?

		a.	B	
	--->	b.	K	
		c.	O
		d.	Q
		e.	R

77.	Why are stars in globular clusters metal-poor, while stars in open clusters are 
	metal-rich?

		a. 	stellar evolution and supernova explosions increase heavy metal 
			numbers

78.	How much does a star's luminosity increase during a typical supernova explosion?

		e.	100,000,000

79.	For what purpose did Charles Messier construct his catalog of objects?

		a.	To assist his search for comets

80.	The "Local Bubble" that is less dense than typical interstellar space was 
	discovered by

		b.	The International Ultraviolet Explorer (IUE)

81.	The interstellar medium is clearly "seen" toward the center of the Milky Way galaxy

		c.	by observing that stars are completely obscured by dust in that 
			direction.

82.	Which of the following lists gives the correct order of luminosity, from highest 
	to lowest?
	
		d.	red giant, sun, white dwarf

83. 	A medium mass star evolves, on the H-R diagram, at the end of its main sequence 
	lifetime

		c.	to higher luminosity and lower surface temperature.

84.	A neutron star has the following properties:

		a.	high density, rapid rotation, high magnetic field.

85.	What does Einstein's theory of relativity tell us that matter does to space?

		e.	Matter warps space

86.	Approximately what temperature in a collapsing protostar will ignite nuclear burning?
	
		e.	8,000,000 K

87.	How long did it take for light from Supernova 1987A to travel to the Earth?

		e.	about 160,000 years

88.	Newborn star clusters are often found with

		a.	emission nebulae.

89.	During the formation of stars, the collapse of globules heats the interstellar gas

		c.	from less than a hundred degrees Kelvin to millions.

90.	The heaviest stars are formed by collapsing clouds
	
		b.	faster than the lightest stars.

91.	Stars of about two solar masses are formed from the collapse of interstellar clouds in

		c.	about 10,000,000 years

92.	Why combine many distant radio telescopes into an interferometer?

		b. 	to obtain much sharper images of sources

93. 	Given a 6000 K surface emits blackbody radiation with a peak wavelength of 0.48 microns

		e.	a 12000 K surface has a peak at 0.24 microns

94.	Star A has a surface temperature of 5000 K and equal area star B has 10,000 K. 

		d.	star B will emit sixteen times the intensity of star A

95. 	Parallax can be used to determine star distances for 

		a.	stars relatively close to the sun

96. 	In understanding stars, the Bohr atom is useful for the following purpose(s):

		b.	it helps us understand the spectral lines

97.	The specific colors of light emitted by an atom in a hot thin gas are caused by

		e.	electrons jumping to lower energy levels, losing energy as they do so.

98.	Stars that are just being formed are best observed by

		e.	radio waves or infrared radiation.

99.	When light from the concave primary mirror of a telescope is reflected by a small 
	secondary mirror through a hole in the primary to its focus, this is called the

		e.	Cassegrain focus