ch.13

Question 1

What fundamental method is used for measuring distances to nearby stars?

Answer 1

Triangulation

Triangulation involves measuring the length of a triangle’s baseline and the angles from the ends of this baseline to a distant object.

Question 2

What is the baseline used in the parallax method for measuring distances?

Answer 2

The Earth’s orbit radius (1 AU)

Parallax involves measuring angles with respect to very distant stars.

Question 3

What is the formula for calculating distance in parsecs using the parallax angle?

Answer 3

d pc = 1/p arc seconds

The parallax angle, p, is half the angular shift of the nearby star.

Question 4

What is a parsec in terms of light-years?

Answer 4

3.26 light-years

A parsec is also equivalent to 3.09 × 10^13 km.

Question 5

What is the nearest star to the Sun and its distance in parsecs?

Answer 5

Proxima Centauri (1.3 pc or 4.3 L.Y)

Proxima Centauri is part of the Alpha Centauri complex.

Question 6

What does the inverse square law relate to in terms of stars?

Answer 6

Luminosity and Apparent Brightness

This principle explains why two stars that appear equally bright can be at different distances.

Question 7

How does a difference of 5 in magnitude correspond to apparent brightness?

Answer 7

Corresponds to a change of a factor of 100

A difference in magnitude of 5 means that one star is 100 times brighter than another.

Question 8

What is the scale of apparent magnitude in astronomy?

Answer 8

The scale runs ‘backward’; high magnitude = low brightness

Larger magnitudes indicate dimmer stars.

Question 9

What is the absolute magnitude of a star?

Answer 9

The apparent magnitude the same star would have at 10 parsecs distance

This allows for a comparison of luminoities without distance dependence.

Question 10

What does the color of a star indicate?

Answer 10

Its temperature

Red stars are cooler, while blue stars are hotter.

Question 11

What type of radiation is emitted by stars?

Answer 11

Blackbody radiation

Wien’s Law relates the temperature to the peak wavelength of emitted light.

Question 12

What can a star’s spectrum reveal?

Answer 12

Composition, temperature, luminosity, velocity in space, rotation speed, and other properties

Sometimes, it may also reveal mass and radius.

Question 13

Who discovered the spectral types of stars are more orderly if rearranged by temperature?

Answer 13

Annie Jump Cannon

The spectral types are O, B, A, F, G, K, M, with O being the hottest and M the coolest.

Question 14

What are the seven general categories of stellar spectra?

Answer 14

O, B, A, F, G, K, M

Each spectral type is divided into 10 subdivisions, with lower numbers indicating hotter stars.

Question 15

What law relates luminosity to temperature and radius of a star?

Answer 15

Stefan-Boltzmann Law

If two stars have the same size, the hotter star will have greater luminosity.

Question 16

What is the formula used to determine a star’s luminosity?

Answer 16

L = σT^4 × 4πR^2

Where L is luminosity, σ is the Stefan-Boltzmann constant, T is temperature, and R is the radius.

Question 17

How do stellar sizes vary?

Answer 17

Dwarf stars (≤ Sun’s radius), Giant stars (10-100 × Sun’s radius), Supergiant stars (> 100 × Sun’s radius)

Stellar radii can differ enormously.

Question 18

What is the Hertzsprung-Russell Diagram?

Answer 18

A plot of stellar luminosity against surface temperature

It helps understand the properties and classifications of stars.

Question 19

What pattern emerges when many stars are plotted on the H-R diagram?

Answer 19

The main sequence where most stars lie

This includes regions for red giants and white dwarfs.

Question 20

What is the method of standard candles in astronomy?

Answer 20

A method to determine distances by measuring apparent brightness and spectral class

This method extends the cosmic distance scale.

Question 21

What are binary stars?

Answer 21

Two stars that revolve around each other due to mutual gravitational attraction

They are essential for measuring stellar masses.

Question 22

What is the modified form of Kepler’s third law used for binary stars?

Answer 22

m + M = P^2/a^3

Where m and M are the binary star masses, P is the period of revolution, and a is the semi-major axis of one star’s orbit.

Question 23

What is the main determinant of a star’s position on the main sequence?

Answer 23

Mass

Stellar lifetime is proportional to stellar mass and luminosity.

Question 24

What is the single most important characteristic in determining the course of a star’s evolution?

Answer 24

mass

Question 25

What is parallax?

Answer 25

The apparent shift in position of an object caused by a change in the observer's position

Question 26

Parallax measurements of the distances to the nearest stars use _____ as a baseline.

Answer 26

Earth's orbit

Question 27

The relative brightness of the stars as we see them in our sky is represented by their _____

Answer 27

Apparent magnitude

Question 28

If Star A and Star B have the same temperatures, but Star A is more luminous than Star B, which of the following must be the case?

Answer 28

Star A is larger than Star B

Question 29

Luminosity (absolute brightness) of a star depends on its ___________.

Answer 29

Both A and B

Question 30

If Star A and Star B have the same size, but Star A is more luminous than Star B, which of the following must be the case?

Answer 30

Star A is hotter than Star B

Question 31

Which of the following stars has the hottest stellar surface temperature?

Answer 31

B2

Question 32

Which of the following stars is reddish in color?

Answer 32

K9

Question 33

In the HR diagram on the x-axis, the temperature increases _____

Answer 33

Toward left

Question 34

In the above HR diagram sketch, which star is a white dwarf?

Answer 34

A

Question 35

In the above HR diagram sketch, which star is a red dwarf?

Answer 35

E

Question 36

In the above HR diagram sketch, which star is a red giant?

Answer 36

B

Question 37

In the above HR diagram sketch, which star is a blue giant?

Answer 37

C

Question 38

In the above HR diagram, which main sequence star is bluish in color?

Answer 38

A

Question 39

In the above HR diagram, which main sequence star is reddish in color?

Answer 39

E

Question 40

In the above HR diagram, which main sequence star is biggest in size?

Answer 40

C

Question 41

A star has a parallax angle of 0.25 arcseconds. It is therefore at a distance of _____

Answer 41

4 parsecs

Question 42

80% of ________ type stars have orbiting companions.

Answer 42

K and M

Question 43

In which binary system can we observe both the stars separately and follow their orbits around each other?

Answer 43

Visual binary system

Question 44

The H-R diagram is a diagram plotting the stars according to their _____

Answer 44

Luminosity and temperature

Question 45

The star Aldebaran is a red giant, and is much more luminous than the Sun. What conclusions can be drawn from this fact?

Answer 45

Aldebaran is cooler than the Sun, but has a larger diameter than the Sun

Question 46

Which of the following is a main sequence star hotter than the Sun?

Answer 46

O2II

Question 47

The star Aldebaran is cooler and much more luminous than the Sun. Where do you expect to find Aldebaran in the H-R diagram?

Answer 47

Top right

Question 48

Which of the following statements would explain the fact that larger molecules, such as amino acids, do not produce spectral lines in the OBAFGKM classification?

Answer 48

All of the above

Question 49

How can we explain the fact that hydrogen Balmer lines are essentially absent in the hot O type and the cool M stars?

Answer 49

In O stars hydrogen is ionized and in M stars the electrons of hydrogen are in level 1, not level 2

Question 50

The spectrum of a star shows the 656 nm absorption line shifted to 658 nm. Which of the following can we conclude about this star?

Answer 50

The star is receding with an approximate speed of 1,800 km/sec

Question 51

Binary star systems are very important because they allow _____

Answer 51

Measurement of star masses

Question 52

What is the difference between spectroscopic and visual binaries?

Answer 52

In a visual binary, we can see two distinct stars; in spectroscopic binaries, the images of the two stars cannot be resolved

Question 53

A visual binary star system has a rotation period P = 10 years. The semi-major axis of the orbit of one of the stars is 10 AU. What is the combined mass of the binary star system?

Answer 53

10 solar masses

Question 54

The study of eclipsing binary stars is very important because it allows astronomers to determine _____

Answer 54

The luminosity of each star

Question 55

Stars on the main sequence have different luminosities because _____

Answer 55

They have different masses

Question 56

Which of the following statements about the mass-luminosity relation is correct?

Answer 56

It relates the luminosity to the mass for main sequence stars only

Question 57

Which of the following is not true for a pulsating star?

Answer 57

They are usually members of an eclipsing binary star system

Question 58

What can we conclude about a star because its luminosity varies in an irregular pattern?

Answer 58

The star is very old

Question 59

The parallax method for determining distances is _____ that uses the _____ as the baseline.

Answer 59

A triangulation; radius of the Earth's orbit

Question 60

_____ can be used to measure the _____ of nearby stars.

Answer 60

Parallax measurements; radius

Question 61

The parallax of a star is _____ usually measured in ____.

Answer 61

An angle; arcseconds

Question 62

A nearby star is more likely to have _____

Answer 62

Large parallax

Question 63

The amount of energy emitted by a star each second is the _____ and is measured in ____.

Answer 63

Luminosity; Watts

Question 64

A light source at a distance of 1 meter that emits 100 Watts of visible radiation has the same _____ as a source emitting 400 Watts and is located _____

Answer 64

Apparent brightness; 2 meters away

Question 65

The luminosity of a star is determined by the star's ___ and ____.

Answer 65

Diameter; surface temperature

Question 66

A star of apparent magnitude 1 appears ______ times brighter than a star of apparent magnitude 2.

Answer 66

2.51

Question 67

A star of apparent magnitude ____ appears 2.51 times brighter than a star of apparent magnitude 4.

Answer 67

1

Question 68

Analysis of stellar spectra shows that most stars consist of 71% ___, 27% ___ and a 2% mix of the other elements.

Answer 68

Hydrogen; helium

Question 69

The Balmer lines correspond to wavelengths in the ____ part of the spectrum of a ____ atom.

Answer 69

Visible; hydrogen

Question 70

The H-R diagram usually graphs the stars according to their luminosity and temperature. An equally valid H-R diagram could be done by plotting the ____ and the ____ of the stars.

Answer 70

Absolute magnitude; temperature

Question 71

An M type star 1000 times more luminous than the Sun will be located near the ___ part of the H-R diagram.

Answer 71

Top right

Question 72

The hydrogen absorption lines are the strongest in ___ type stars.

Answer 72

A

Question 73

Lines from molecules are strongest in the cool ___ type stars.

Answer 73

M

Question 74

In ___ stars most of the electrons in the hydrogen atom are above level 2 and in ___ stars most of the electrons are below level 2, therefore the _____ are essentially absent in both types.

Answer 74

Type O; type M; Balmer lines

Question 75

____ binary star systems are important because they allow astronomers to determine the mass and the ____ of the stars in the system.

Answer 75

Spectroscopic; temperature

Question 76

Analysis of ___ stars has shown that star masses are in the range of ___ to ____ solar masses.

Answer 76

Binary; 1; 10

Question 77

A main sequence star has 2 times the mass of the Sun. Using ____ we find that the star is ___ times more luminous than the Sun.

Answer 77

The mass-luminosity relation; 8

Question 78

White dwarfs have ____ spectral lines than red giants.

Question 79

A main sequence star has 2 times the mass of the Sun. Using ____ we find that the star is ___ times more luminous than the Sun.

Answer 79

The mass-luminosity relation; 8 ## Footnote The mass-luminosity relation indicates that luminosity increases with the mass of a star, particularly for main sequence stars.

Question 80

White dwarfs have ____ spectral lines than red giants.

Answer 80

Narrower ## Footnote White dwarfs exhibit narrower spectral lines due to their higher surface temperatures compared to red giants.

Question 81

In the H-R diagram, a star of luminosity class ___ will be located ____.

Answer 81

II; above the luminosity class I stars ## Footnote The H-R diagram categorizes stars based on their luminosity and temperature, with different classes indicating their evolutionary stages.

Question 82

A star with a spectrum that peaks at a wavelength of 1 micron (1 × 10^-6) would have a surface temperature of _________ and be an _________ star.

Answer 82

2900 K, M ## Footnote The peak wavelength can be used to determine the temperature of a star using Wien's law.

Question 83

True or False: The hottest (O and B type) stars are usually binary stars, while the coolest (M type) stars are usually single stars.

Answer 83

True ## Footnote Binary systems are more commonly found among hotter stars due to their formation processes.

Question 84

True or False: Nearby stars have smaller parallax angles, therefore their distance in parsecs is smaller.

Answer 84

False ## Footnote Nearby stars have larger parallax angles, which correspond to smaller distances in parsecs.

Question 85

True or False: Wien's law implies that a yellow star is hotter than a red star.

Answer 85

True ## Footnote Wien's law states that hotter objects emit light at shorter wavelengths.

Question 86

True or False: Wien's law can only tell us about the surface temperature of a star, not the temperatures of the invisible interior of a star.

Answer 86

True ## Footnote Wien's law applies to the emitted radiation from the surface, not the internal structure.

Question 87

True or False: The luminosity of a star allows astronomers to determine the radius and distance of the star.

Answer 87

True ## Footnote Luminosity is key to calculating the radius using the Stefan-Boltzmann law.

Question 88

True or False: The absolute magnitude of a star tells us how bright the star would appear if placed at a distance of 10 pc from the Sun.

Answer 88

True ## Footnote Absolute magnitude is a standardized measure of a star's brightness at a specific distance.

Question 89

True or False: A star of absolute magnitude 1 is about 2.51 times more luminous than a star of absolute magnitude 2.

Answer 89

True ## Footnote The difference in absolute magnitudes corresponds to a factor of 2.51 in luminosity.

Question 90

True or False: A star with an apparent magnitude of 10 is visible by the naked eye.

Answer 90

False ## Footnote Stars with apparent magnitudes around 6 or lower are typically visible to the naked eye.

Question 91

True or False: One parsec is equal to 3.26 light years.

Answer 91

True ## Footnote This is a standard conversion factor in astronomy.

Question 92

True or False: The Sun is a G2V type star.

Answer 92

True ## Footnote The Sun is classified as a G-type main-sequence star.

Question 93

True or False: The sequence OBAFGKM orders the stars in decreasing temperature and decreasing mass.

Answer 93

True ## Footnote This classification is based on spectral types and their corresponding temperatures and masses.

Question 94

True or False: Hydrogen Balmer lines are essentially absent in the O and M type stars.

Answer 94

True ## Footnote The presence of Balmer lines is most prominent in A and F type stars.

Question 95

True or False: A star approaching the Earth will show spectral lines that are shifted to shorter wavelengths.

Answer 95

True ## Footnote This phenomenon is known as the Doppler effect.

Question 96

True or False: Measuring stellar masses using binary stars is difficult because binary stars are rare.

Answer 96

False ## Footnote Binary stars are common and provide valuable data for measuring stellar masses.

Question 97

True or False: The masses of stars are generally in the range of 30 to 0.1 solar masses.

Answer 97

True ## Footnote Stellar masses can vary widely, but this range encompasses most observed stars.

Question 98

True or False: The study of eclipsing binary star systems provides information about the radii of stars.

Answer 98

True ## Footnote Eclipsing binaries allow for precise measurements of stellar sizes and orbits.

Question 99

True or False: The mass-luminosity relation applies to main-sequence stars only.

Answer 99

True ## Footnote This relationship holds primarily for stars during their main sequence phase.

Question 100

True or False: The H-R diagram shows that stars begin their life as red giants, contract and heat-up with age and progress from right to left along the main sequence.

Answer 100

False ## Footnote Stars generally start on the main sequence before evolving into red giants.

Question 101

True or False: The luminosity class of a star can be determined from the width of the spectral lines of the star.

Answer 101

True ## Footnote The width of spectral lines indicates pressure and density, which relate to luminosity class.

Question 102

True or False: In the H-R diagram, stars of luminosity class Ia are located near the center.

Answer 102

False ## Footnote Class Ia stars, which are supergiants, are typically found above the main sequence in the H-R diagram.