Astronomy 122 - Exam 2 answers

1.	The most common element of main-sequence stars is

		a.	hydrogen 

2.	The radius of the Sun is about

		c.	700,000 kilometers

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

4.	The interstellar gas (by number of atoms) is

		a.	90% hydrogen, 9% helium, traces of other atoms

5.	HII regions are characterized by

		a.	ionized hydrogen

6.	A solar flare is

		d.	an explosion on the solar surface

7.	Which of the following statements is true?

		a.	a red giantŐs radius may be tens to hundreds of times the radius of the Sun

8.	Which of the following terms is equivalent to brightness?

		d.	apparent magnitude

9.	Energy is transferred from the solar core to the bottom of the convection zone by

		a.	radiation

10.	Solar granulation is an indication that

		c.	energy is transported out of the Sun by convection

11.	Approximately what fraction of stars within our local neighborhood are main sequence stars?

		d.	90 %

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

		d.	1 atom/cm3

13.	The radial motion of a star is determined by

		a.	the Doppler shift of its absorption lines

14.	Which of the following four spectral classifications represents the hottest stellar surface 
	temperature of these four?

		a.	A
	-->	b.	B
		c.	G
		d.	K

15.	Which of the following four spectral classifications represents the coolest stellar surface 
	temperature of these four?

		a.	B
	-->	b.	K
		c.	A
		d.	G

16.	The visible corona of the Sun is most effectively photographed 

		c.	during solar eclipses

17.	Which of the following terms is equivalent to luminosity?

		c.	absolute magnitude

18.	What is the luminosity class of the Sun?

		d.	V

19.	Stars on the main sequence

		b.	generate energy by thermonuclear fusion in their cores

20.	What is the approximate expected main sequence lifetime of a star with a mass of 15 solar masses?

		d.	about 15 million years

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

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

22.	Which of the following is NOT the effect of interstellar dust on starlight?

	-->	a.	mutation	
		b.	extinction
		c.	reddening
		d.	polarization

23.	The age of the Sun is about

		c.	  5,000,000,000 years

24. 	The luminosity of a star is a unique measure of its

		c.	total energy output

25.	In the spectral sequence of star types, in which each spectral class has been divided 
	into 10 intervals, the Sun is classified as

		d.	G  2

26.	Which of the following lists gives the order of star spectral classes from hottest to coolest?

		d.	O B A F G K M

27.	We understand that stars above the main sequence of the H-R diagram are the 
	result of:

		c.	stars with larger surface areas

28.	The brightest star in the night sky is:

		d.	Sirius
 
29. 	What proportion of visible stars in the nighttime sky are multiple-star systems, such as double stars?

		a. most stars   

30.	The relationship between mass and luminosity of stars on the Main Sequence is that

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

31. 	The Sun's source of energy at the present time is  

		d.	thermonuclear fusion (combination) of hydrogen atoms

32. 	The evolution of a star depends predominantly upon

		d.	its initial mass
	
33.	The surface temperature of a B type star is about

		c.	20,000 K

34.	Giant magnetic bubbles of ionized gas that separate from the SunŐs atmosphere and escape 
	into interplanetary space are called

		a.	coronal mass ejections

35.	The surface temperature of a red star is about

		a.	3000 K

36.	A reflection nebula

		a.	is bluish in color

37.	Compared to an excellent, research quality vacuum on Earth, the density of gas in the interstellar medium is

		a.	the interstellar medium is much less dense.

38.	The chemical composition of the surface layers of the Sun is determined primarily by what technique?

		a.	spectroscopy

39.	One particular feature of the solar corona is

		c.	its very high temperature

40. 	The brightest stars in the sky were labeled by the Greeks as

		a.	magnitude 1 stars

41. 	Star A is magnitude 3 and Star B is magnitude 8

		a.	Star A is 100 times brighter than Star B

42.	The temperature of the core of the Sun, where thermonuclear processes can take place, is approximately 

		d.	1.5 x 107 K

43.	The average time taken for energy generated by thermonuclear fusion in the center of the Sun to 
	reach the surface layers and escape is calculated to be

		d.	tens or hundreds of thousands of years

44.	The Sun has been stable for a very long time, in hydrostatic equilibrium.  Which two parameters must 
	be in balance within the Sun?

		d.	the force of gravity and outward gas pressure

45.	The Horsehead Nebula is

		a.	an absorption nebula

46.	What processes of heat energy transfer are important within the Sun?

		b.	radiation and convection

47.	The total time that the Sun will spend as a main sequence star is 

		a.	about 10 billion years (1010 years)

48.	The most common molecule in a molecular cloud is

		b.	molecular hydrogen, H2

49.	On the Hertzsprung-Russell diagram which type of star has the following characteristics:  
	A star with surface temperature 10,000 K, and luminosity 1/100 times that of the Sun.

		d.	white dwarf

50.	Main-sequence stars of which of the following spectral classes have the greatest mass?

		b.	O	

51.	Which of the following regions would be hottest?

		a.	Death Valley
		b.	HI regions
	-->	c.	HII regions
		d.	molecular clouds

52.	An eclipsing binary system is

		a.	two stars which periodically eclipse each other, as seen from Earth

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

		a.	stellar mass

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

		c.	the distance from the earth to the Sun

55.	Spectroscopic parallax is used to 

		d.	determine the distance to main-sequence stars

56.	Which of the following main sequence stars would have the coolest surface?

		a.	Spectral Class A
	-->	b.	Spectral Class M
		c.	Spectral Class O
		d.	Spectral Class T

57.	What is HII?
 
		c.	ionized hydrogen

58.	Which of the following is an absorption nebula?

		c.	The Horsehead Nebula

59.	The distance from the Earth to the Sun is

		d.	150,000,000 kilometers 

60.	A coronal hole is

		d.	a hole in the Sun's corona

61.	A good example of a reflection nebula is

		d.	The Pleiades

62.	The 21-cm line comes from

		b.	spin-flip of the electron in hydrogen

63.	How does the temperature of a Sunspot compare to the temperature of the 
	solar surface?

		d.	colder in both hemispheres

64.	The solar constant is

		a.	1400 Watts/m2

65.	Differential rotation of the Sun refers to

		c.	the rapid speed of the rotation of the equator of the Sun		

66.	Which of the following spectral classes of stars has the longest main-sequence lifetime?

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

67.	Which of the following spectral classes of stars has the longest main-sequence lifetime?

		a.	K
	-->	b.	M
		c.	O
		d.	Q

68.	The radius of a main sequence star can be determined from

		a.	Luminosity and surface temperature

69.	A star's luminosity class is determined from

		a.	the width of its absorption lines

70.	A good example of an absorption (or dark) nebula is

		a.	The Horsehead Nebula

71.	The distinctive color of a reflection nebula is

		b.	blue, caused by the scattering of light from dust grains

72.	What is the approximate ratio of hydrogen to helium in the interstellar medium, 
	by number of atoms?

		b.	10 to 1

73.	The rotation period of the Solar equator is 

		c.	25 days

74.	Which of the following lists the types of stars from smallest radius to largest

		d.	white dwarf, Sun, red giant

75.	The oldest star clusters are

		d.	globular clusters

76.	The interstellar medium is mostly composed of

		d.	diffuse gas composed of hydrogen and helium

77.	The surface temperature of a red giant is likely to be about

		b.	  4,500 K

78.	The surface temperature of a white dwarf is likely to be about
		
		c.	 10,000 K 

79.	When a neutrino from the Sun reaches the Earth, what is the most likely outcome?

		a.	it passes right through the Earth, unchanged

80.	Which of the following are NOT main-sequence stars

		a.	white dwarfs
		b.	red giants
		c.	red supergiants
	--->	d.	all of the above

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

		a.	To assist his search for comets

82.	A good example of an emission nebula is

		d.	The Orion Nebula

83.	Which of the following regions would be coldest?

		a.	HI regions
		b.	HII regions
	-->	c.	molecular clouds
		d.	my dorm room

84.	The effective reaction for the proton-proton chain is

		b.	4(H) --> He + neutrinos + energy


SHORT QUESTIONS

86.	Write an equation relating luminosity, radius, and surface temperature of a star.

		Luminosity ∼ Radius2 x Temperature4

87.	What is the second most abundant element in the Sun?

		Helium

88.	Name a star in the constellation Orion that is large enough to be having its 
	size resolved directly.

		Betelguese

89.	How often does the number of Sunspots on the solar surface reach a maximum?  

		Every 11 years

90.	What is the preferential dimming of short-wavelengths by dust in the 
	interstellar medium called?

		Extinction

91.	What is the energy transfer process that operates in the Sun via mass motion?

		Convection

92.	What is the Luminosity Class of the main-sequence stars?

		V

93. 	The Nebula around the Pleiades is an example of what type of nebula?

		Reflection Nebula