Option E: astrophysics

Question 1

Stellar cluster

Answer 1

a group of stars that are physically close together rather than looking as though they are. These are formed by the collapse of a gas cloud.

Question 2

Constellation

Answer 2

the result of ancient civilizations playing `join the dots´ with the stars. The stars are not related by anything physically except maybe that they are all bright.

Question 3

light year

Answer 3

This is equal to the distance travelled by light in one year

Question 4

the luminosity of a star

Answer 4

The total amount of energy emitted by the star per second

Question 5

Apparent brightness

Answer 5

the amount of energy per second received per unit area

Question 6

Wien´s law

Answer 6

The relationship between the peak wavelength on the graph of Stephan-Boltzmann graph and the temperature is given by Wien displacement graph.

Question 7

Explain how atomic spectra may be used to deduce chemical and physical data for stars

Answer 7

1. To put it simply, spectra reveal the presence of elements, ions, and molecules.
2. Spectra indicate temperature of the object.
3. Spectra indicate doppler motion of the object.

Question 8

binary stars

Answer 8

A binary star is a stellar system consisting of two stars orbiting around their center of mass

Question 9

red giants

Answer 9

very large, but low surface temperature. They have exhausted their supply of hydrogen in their cores and switched to fusing hydrogen in a shell outside the core. Since the inert helium core has no source of energy of its own, it contracts and heats up, and its gravity compresses the hydrogen in the layer immediately above it, causing it to fuse faster. This in turn causes the star to become more luminous

Question 10

white dwarfs

Answer 10

smaller than Sun, very hot …. produced when a low or medium mass star dies. These stars are not heavy enough to generate the core temperatures required to fuse carbon in nucleosynthesis reactions. Eventually, over hundreds of billions of years, white dwarfs will cool to temperatures at which they are no longer visible. As a class, white dwarfs are fairly common; they comprise roughly 6% of all stars.

Question 11

A visual binary star

Answer 11

is a binary star for which the angular separation is great enough to permit them to be observed as a double star in a telescope. The resolving power of the telescope is an important factor in the detection of visual binaries, and as telescopes become larger and more powerful an increasing number of visual binaries will be detected. The brightness of the two stars is also an important factor, as brighter stars are harder to separate due to their glare than dimmer ones are.

Question 12

A spectroscopic binary star

Answer 12

is a binary star in which the separation between the stars is usually very small, and the orbital velocity very high. A Doppler shift occurs when they move towards/away from you so the spectrum regularly changes.

Question 13

An eclipsing binary star

Answer 13

is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. Eclipsing binaries are variable stars, not because the light of the individual components vary, but because of the eclipses.

Question 14

Parsec

Answer 14

the distance at which one Au subtends an angle of one second

Question 15

Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec

Answer 15

oDue to the bend of light by the atmosphere, it is not possible to measure angles smaller than 0.001arc sec on earth.
oThe means that distances greater than 100pc cannot be measured.

Question 16

Describe the apparent magnitude scale

Answer 16

Students should know that apparent magnitude depends on luminosity and the distance to a star. They should also know that a magnitude 1 star is 100 times brighter than a magnitude 6 star.

Question 17

Absolute magnitude

Answer 17

the magnitude of a star viewed from a distance of 10pc

Question 18

Outline the nature of a Cepheid variable

Answer 18

(Students should know that a Cepheid variable is a star in which the outer layers undergo a periodic expansion and contraction, which produces a periodic variation in its luminosity)
•For stars further away than 10Mpc the amount of light received is too small to accurately determine their temperature. In this case an alternative method is used that involves measuring the time period of a flashing star.
•A Cepheid variable is an unstable star that undergoes periodic expansions and contractions, leading to a periodic change in the apparent brightness of the star, as viewed from Earth.

Question 19

State the relationship between period and absolute magnitude for Cepheid variables

Answer 19

• The period and luminosity are related, proportional towards each other
• Cepheid variables may be used as “standard candles” to check other methods. If a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined by using the luminosity–period relationship.

Question 20

Explain how Cepheid variables may be used as “standard candles”

Answer 20

It is sufficient for students to know that, if a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined.

Question 21

Describe Newton´s model of the universe

Answer 21

Students should know that Newton assumed an infinite (in space and time), uniform and static universe.

Question 22

Explain Olbers´ paradox

Answer 22

Students should be able to show quantitatively, using the inverse square law of luminosity, that Newton´s model of the universe leads to a sky that should never be dark.

Question 23

How can we see that the universe is expanding?

Answer 23

the red-shift of light from galaxies indicate that the universe is expanding.

Question 24

A visual binary star

Answer 24

is a binary star for which the angular separation is great enough to permit them to be observed as a double star in a telescope. The resolving power of the telescope is an important factor in the detection of visual binaries, and as telescopes become larger and more powerful an increasing number of visual binaries will be detected. The brightness of the two stars is also an important factor, as brighter stars are harder to separate due to their glare than dimmer ones are.

Question 25

A spectroscopic binary star

Answer 25

is a binary star in which the separation between the stars is usually very small, and the orbital velocity very high. A Doppler shift occurs when they move towards/away from you so the spectrum regularly changes.

Question 26

An eclipsing binary star

Answer 26

is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. Eclipsing binaries are variable stars, not because the light of the individual components vary, but because of the eclipses.

Question 27

Parsec

Answer 27

the distance at which one Au subtends an angle of one second

Question 28

Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec

Answer 28

oDue to the bend of light by the atmosphere, it is not possible to measure angles smaller than 0.001arc sec on earth.
oThe means that distances greater than 100pc cannot be measured.

Question 29

Describe the apparent magnitude scale

Answer 29

Students should know that apparent magnitude depends on luminosity and the distance to a star. They should also know that a magnitude 1 star is 100 times brighter than a magnitude 6 star.

Question 30

Absolute magnitude

Answer 30

the magnitude of a star viewed from a distance of 10pc

Question 31

Outline the nature of a Cepheid variable

Answer 31

(Students should know that a Cepheid variable is a star in which the outer layers undergo a periodic expansion and contraction, which produces a periodic variation in its luminosity)
•For stars further away than 10Mpc the amount of light received is too small to accurately determine their temperature. In this case an alternative method is used that involves measuring the time period of a flashing star.
•A Cepheid variable is an unstable star that undergoes periodic expansions and contractions, leading to a periodic change in the apparent brightness of the star, as viewed from Earth.

Question 32

State the relationship between period and absolute magnitude for Cepheid variables

Answer 32

• The period and luminosity are related, proportional towards each other
• Cepheid variables may be used as “standard candles” to check other methods. If a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined by using the luminosity–period relationship.

Question 33

Explain how Cepheid variables may be used as “standard candles”

Answer 33

It is sufficient for students to know that, if a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined.

Question 34

Describe Newton´s model of the universe

Answer 34

Students should know that Newton assumed an infinite (in space and time), uniform and static universe.

Question 35

Explain Olbers´ paradox

Answer 35

Students should be able to show quantitatively, using the inverse square law of luminosity, that Newton´s model of the universe leads to a sky that should never be dark.

Question 36

How can we see that the universe is expanding?

Answer 36

the red-shift of light from galaxies indicate that the universe is expanding.

Question 37

A visual binary star

Answer 37

is a binary star for which the angular separation is great enough to permit them to be observed as a double star in a telescope. The resolving power of the telescope is an important factor in the detection of visual binaries, and as telescopes become larger and more powerful an increasing number of visual binaries will be detected. The brightness of the two stars is also an important factor, as brighter stars are harder to separate due to their glare than dimmer ones are.

Question 38

A spectroscopic binary star

Answer 38

is a binary star in which the separation between the stars is usually very small, and the orbital velocity very high. A Doppler shift occurs when they move towards/away from you so the spectrum regularly changes.

Question 39

An eclipsing binary star

Answer 39

is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. Eclipsing binaries are variable stars, not because the light of the individual components vary, but because of the eclipses.

Question 40

Parsec

Answer 40

the distance at which one Au subtends an angle of one second

Question 41

Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec

Answer 41

oDue to the bend of light by the atmosphere, it is not possible to measure angles smaller than 0.001arc sec on earth.
oThe means that distances greater than 100pc cannot be measured.

Question 42

Describe the apparent magnitude scale

Answer 42

Students should know that apparent magnitude depends on luminosity and the distance to a star. They should also know that a magnitude 1 star is 100 times brighter than a magnitude 6 star.

Question 43

Absolute magnitude

Answer 43

the magnitude of a star viewed from a distance of 10pc

Question 44

Outline the nature of a Cepheid variable

Answer 44

(Students should know that a Cepheid variable is a star in which the outer layers undergo a periodic expansion and contraction, which produces a periodic variation in its luminosity)
•For stars further away than 10Mpc the amount of light received is too small to accurately determine their temperature. In this case an alternative method is used that involves measuring the time period of a flashing star.
•A Cepheid variable is an unstable star that undergoes periodic expansions and contractions, leading to a periodic change in the apparent brightness of the star, as viewed from Earth.

Question 45

State the relationship between period and absolute magnitude for Cepheid variables

Answer 45

• The period and luminosity are related, proportional towards each other
• Cepheid variables may be used as “standard candles” to check other methods. If a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined by using the luminosity–period relationship.

Question 46

Explain how Cepheid variables may be used as “standard candles”

Answer 46

It is sufficient for students to know that, if a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined.

Question 47

Describe Newton´s model of the universe

Answer 47

Students should know that Newton assumed an infinite (in space and time), uniform and static universe.

Question 48

Explain Olbers´ paradox

Answer 48

Students should be able to show quantitatively, using the inverse square law of luminosity, that Newton´s model of the universe leads to a sky that should never be dark.

Question 49

How can we see that the universe is expanding?

Answer 49

the red-shift of light from galaxies indicate that the universe is expanding.

Question 50

A visual binary star

Answer 50

is a binary star for which the angular separation is great enough to permit them to be observed as a double star in a telescope. The resolving power of the telescope is an important factor in the detection of visual binaries, and as telescopes become larger and more powerful an increasing number of visual binaries will be detected. The brightness of the two stars is also an important factor, as brighter stars are harder to separate due to their glare than dimmer ones are.

Question 50

A visual binary star

Answer 50

is a binary star for which the angular separation is great enough to permit them to be observed as a double star in a telescope. The resolving power of the telescope is an important factor in the detection of visual binaries, and as telescopes become larger and more powerful an increasing number of visual binaries will be detected. The brightness of the two stars is also an important factor, as brighter stars are harder to separate due to their glare than dimmer ones are.

Question 51

A spectroscopic binary star

Answer 51

is a binary star in which the separation between the stars is usually very small, and the orbital velocity very high. A Doppler shift occurs when they move towards/away from you so the spectrum regularly changes.

Question 51

A spectroscopic binary star

Answer 51

is a binary star in which the separation between the stars is usually very small, and the orbital velocity very high. A Doppler shift occurs when they move towards/away from you so the spectrum regularly changes.

Question 52

An eclipsing binary star

Answer 52

is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. Eclipsing binaries are variable stars, not because the light of the individual components vary, but because of the eclipses.

Question 52

An eclipsing binary star

Answer 52

is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. Eclipsing binaries are variable stars, not because the light of the individual components vary, but because of the eclipses.

Question 53

Parsec

Answer 53

the distance at which one Au subtends an angle of one second

Question 53

Parsec

Answer 53

the distance at which one Au subtends an angle of one second

Question 54

Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec

Answer 54

oDue to the bend of light by the atmosphere, it is not possible to measure angles smaller than 0.001arc sec on earth.
oThe means that distances greater than 100pc cannot be measured.

Question 54

Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec

Answer 54

oDue to the bend of light by the atmosphere, it is not possible to measure angles smaller than 0.001arc sec on earth.
oThe means that distances greater than 100pc cannot be measured.

Question 55

Describe the apparent magnitude scale

Answer 55

Students should know that apparent magnitude depends on luminosity and the distance to a star. They should also know that a magnitude 1 star is 100 times brighter than a magnitude 6 star.

Question 55

Describe the apparent magnitude scale

Answer 55

Students should know that apparent magnitude depends on luminosity and the distance to a star. They should also know that a magnitude 1 star is 100 times brighter than a magnitude 6 star.

Question 56

Absolute magnitude

Answer 56

the magnitude of a star viewed from a distance of 10pc

Question 56

Absolute magnitude

Answer 56

the magnitude of a star viewed from a distance of 10pc

Question 57

Outline the nature of a Cepheid variable

Answer 57

(Students should know that a Cepheid variable is a star in which the outer layers undergo a periodic expansion and contraction, which produces a periodic variation in its luminosity)
•For stars further away than 10Mpc the amount of light received is too small to accurately determine their temperature. In this case an alternative method is used that involves measuring the time period of a flashing star.
•A Cepheid variable is an unstable star that undergoes periodic expansions and contractions, leading to a periodic change in the apparent brightness of the star, as viewed from Earth.

Question 57

Outline the nature of a Cepheid variable

Answer 57

(Students should know that a Cepheid variable is a star in which the outer layers undergo a periodic expansion and contraction, which produces a periodic variation in its luminosity)
•For stars further away than 10Mpc the amount of light received is too small to accurately determine their temperature. In this case an alternative method is used that involves measuring the time period of a flashing star.
•A Cepheid variable is an unstable star that undergoes periodic expansions and contractions, leading to a periodic change in the apparent brightness of the star, as viewed from Earth.

Question 58

State the relationship between period and absolute magnitude for Cepheid variables

Answer 58

• The period and luminosity are related, proportional towards each other
• Cepheid variables may be used as “standard candles” to check other methods. If a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined by using the luminosity–period relationship.

Question 58

State the relationship between period and absolute magnitude for Cepheid variables

Answer 58

• The period and luminosity are related, proportional towards each other
• Cepheid variables may be used as “standard candles” to check other methods. If a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined by using the luminosity–period relationship.

Question 59

Explain how Cepheid variables may be used as “standard candles”

Answer 59

It is sufficient for students to know that, if a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined.

Question 59

Explain how Cepheid variables may be used as “standard candles”

Answer 59

It is sufficient for students to know that, if a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined.

Question 60

Describe Newton´s model of the universe

Answer 60

Students should know that Newton assumed an infinite (in space and time), uniform and static universe.

Question 60

Describe Newton´s model of the universe

Answer 60

Students should know that Newton assumed an infinite (in space and time), uniform and static universe.

Question 61

Explain Olbers´ paradox

Answer 61

Students should be able to show quantitatively, using the inverse square law of luminosity, that Newton´s model of the universe leads to a sky that should never be dark.

Question 61

Explain Olbers´ paradox

Answer 61

Students should be able to show quantitatively, using the inverse square law of luminosity, that Newton´s model of the universe leads to a sky that should never be dark.

Question 62

How can we see that the universe is expanding?

Answer 62

the red-shift of light from galaxies indicate that the universe is expanding.

Question 62

How can we see that the universe is expanding?

Answer 62

the red-shift of light from galaxies indicate that the universe is expanding.

Question 63

A visual binary star

Answer 63

is a binary star for which the angular separation is great enough to permit them to be observed as a double star in a telescope. The resolving power of the telescope is an important factor in the detection of visual binaries, and as telescopes become larger and more powerful an increasing number of visual binaries will be detected. The brightness of the two stars is also an important factor, as brighter stars are harder to separate due to their glare than dimmer ones are.

Question 63

A visual binary star

Answer 63

is a binary star for which the angular separation is great enough to permit them to be observed as a double star in a telescope. The resolving power of the telescope is an important factor in the detection of visual binaries, and as telescopes become larger and more powerful an increasing number of visual binaries will be detected. The brightness of the two stars is also an important factor, as brighter stars are harder to separate due to their glare than dimmer ones are.

Question 64

A spectroscopic binary star

Answer 64

is a binary star in which the separation between the stars is usually very small, and the orbital velocity very high. A Doppler shift occurs when they move towards/away from you so the spectrum regularly changes.

Question 64

A spectroscopic binary star

Answer 64

is a binary star in which the separation between the stars is usually very small, and the orbital velocity very high. A Doppler shift occurs when they move towards/away from you so the spectrum regularly changes.

Question 65

An eclipsing binary star

Answer 65

is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. Eclipsing binaries are variable stars, not because the light of the individual components vary, but because of the eclipses.

Question 65

An eclipsing binary star

Answer 65

is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. Eclipsing binaries are variable stars, not because the light of the individual components vary, but because of the eclipses.

Question 66

Parsec

Answer 66

the distance at which one Au subtends an angle of one second

Question 66

Parsec

Answer 66

the distance at which one Au subtends an angle of one second

Question 67

Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec

Answer 67

oDue to the bend of light by the atmosphere, it is not possible to measure angles smaller than 0.001arc sec on earth.
oThe means that distances greater than 100pc cannot be measured.

Question 67

Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec

Answer 67

oDue to the bend of light by the atmosphere, it is not possible to measure angles smaller than 0.001arc sec on earth.
oThe means that distances greater than 100pc cannot be measured.

Question 68

Describe the apparent magnitude scale

Answer 68

Students should know that apparent magnitude depends on luminosity and the distance to a star. They should also know that a magnitude 1 star is 100 times brighter than a magnitude 6 star.

Question 68

Describe the apparent magnitude scale

Answer 68

Students should know that apparent magnitude depends on luminosity and the distance to a star. They should also know that a magnitude 1 star is 100 times brighter than a magnitude 6 star.

Question 69

Absolute magnitude

Answer 69

the magnitude of a star viewed from a distance of 10pc

Question 69

Absolute magnitude

Answer 69

the magnitude of a star viewed from a distance of 10pc

Question 70

Outline the nature of a Cepheid variable

Answer 70

(Students should know that a Cepheid variable is a star in which the outer layers undergo a periodic expansion and contraction, which produces a periodic variation in its luminosity)
•For stars further away than 10Mpc the amount of light received is too small to accurately determine their temperature. In this case an alternative method is used that involves measuring the time period of a flashing star.
•A Cepheid variable is an unstable star that undergoes periodic expansions and contractions, leading to a periodic change in the apparent brightness of the star, as viewed from Earth.

Question 70

Outline the nature of a Cepheid variable

Answer 70

(Students should know that a Cepheid variable is a star in which the outer layers undergo a periodic expansion and contraction, which produces a periodic variation in its luminosity)
•For stars further away than 10Mpc the amount of light received is too small to accurately determine their temperature. In this case an alternative method is used that involves measuring the time period of a flashing star.
•A Cepheid variable is an unstable star that undergoes periodic expansions and contractions, leading to a periodic change in the apparent brightness of the star, as viewed from Earth.

Question 71

State the relationship between period and absolute magnitude for Cepheid variables

Answer 71

• The period and luminosity are related, proportional towards each other
• Cepheid variables may be used as “standard candles” to check other methods. If a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined by using the luminosity–period relationship.

Question 71

State the relationship between period and absolute magnitude for Cepheid variables

Answer 71

• The period and luminosity are related, proportional towards each other
• Cepheid variables may be used as “standard candles” to check other methods. If a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined by using the luminosity–period relationship.

Question 72

Explain how Cepheid variables may be used as “standard candles”

Answer 72

It is sufficient for students to know that, if a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined.

Question 72

Explain how Cepheid variables may be used as “standard candles”

Answer 72

It is sufficient for students to know that, if a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined.

Question 73

Describe Newton´s model of the universe

Answer 73

Students should know that Newton assumed an infinite (in space and time), uniform and static universe.

Question 73

Describe Newton´s model of the universe

Answer 73

Students should know that Newton assumed an infinite (in space and time), uniform and static universe.

Question 74

Explain Olbers´ paradox

Answer 74

Students should be able to show quantitatively, using the inverse square law of luminosity, that Newton´s model of the universe leads to a sky that should never be dark.

Question 74

Explain Olbers´ paradox

Answer 74

Students should be able to show quantitatively, using the inverse square law of luminosity, that Newton´s model of the universe leads to a sky that should never be dark.

Question 75

How can we see that the universe is expanding?

Answer 75

the red-shift of light from galaxies indicate that the universe is expanding.

Question 75

How can we see that the universe is expanding?

Answer 75

the red-shift of light from galaxies indicate that the universe is expanding.

Question 76

A visual binary star

Answer 76

is a binary star for which the angular separation is great enough to permit them to be observed as a double star in a telescope. The resolving power of the telescope is an important factor in the detection of visual binaries, and as telescopes become larger and more powerful an increasing number of visual binaries will be detected. The brightness of the two stars is also an important factor, as brighter stars are harder to separate due to their glare than dimmer ones are.

Question 77

A spectroscopic binary star

Answer 77

is a binary star in which the separation between the stars is usually very small, and the orbital velocity very high. A Doppler shift occurs when they move towards/away from you so the spectrum regularly changes.

Question 78

An eclipsing binary star

Answer 78

is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. Eclipsing binaries are variable stars, not because the light of the individual components vary, but because of the eclipses.

Question 79

Parsec

Answer 79

the distance at which one Au subtends an angle of one second

Question 80

Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec

Answer 80

oDue to the bend of light by the atmosphere, it is not possible to measure angles smaller than 0.001arc sec on earth.
oThe means that distances greater than 100pc cannot be measured.

Question 81

Describe the apparent magnitude scale

Answer 81

Students should know that apparent magnitude depends on luminosity and the distance to a star. They should also know that a magnitude 1 star is 100 times brighter than a magnitude 6 star.

Question 82

Absolute magnitude

Answer 82

the magnitude of a star viewed from a distance of 10pc

Question 83

Outline the nature of a Cepheid variable

Answer 83

(Students should know that a Cepheid variable is a star in which the outer layers undergo a periodic expansion and contraction, which produces a periodic variation in its luminosity)
•For stars further away than 10Mpc the amount of light received is too small to accurately determine their temperature. In this case an alternative method is used that involves measuring the time period of a flashing star.
•A Cepheid variable is an unstable star that undergoes periodic expansions and contractions, leading to a periodic change in the apparent brightness of the star, as viewed from Earth.

Question 84

State the relationship between period and absolute magnitude for Cepheid variables

Answer 84

• The period and luminosity are related, proportional towards each other
• Cepheid variables may be used as “standard candles” to check other methods. If a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined by using the luminosity–period relationship.

Question 85

Explain how Cepheid variables may be used as “standard candles”

Answer 85

It is sufficient for students to know that, if a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined.

Question 86

Describe Newton´s model of the universe

Answer 86

Students should know that Newton assumed an infinite (in space and time), uniform and static universe.

Question 87

Explain Olbers´ paradox

Answer 87

Students should be able to show quantitatively, using the inverse square law of luminosity, that Newton´s model of the universe leads to a sky that should never be dark.

Question 88

How can we see that the universe is expanding?

Answer 88

the red-shift of light from galaxies indicate that the universe is expanding.

Question 89

A visual binary star

Answer 89

is a binary star for which the angular separation is great enough to permit them to be observed as a double star in a telescope. The resolving power of the telescope is an important factor in the detection of visual binaries, and as telescopes become larger and more powerful an increasing number of visual binaries will be detected. The brightness of the two stars is also an important factor, as brighter stars are harder to separate due to their glare than dimmer ones are.

Question 90

A spectroscopic binary star

Answer 90

is a binary star in which the separation between the stars is usually very small, and the orbital velocity very high. A Doppler shift occurs when they move towards/away from you so the spectrum regularly changes.

Question 91

An eclipsing binary star

Answer 91

is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. Eclipsing binaries are variable stars, not because the light of the individual components vary, but because of the eclipses.

Question 92

Parsec

Answer 92

the distance at which one Au subtends an angle of one second

Question 93

Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec

Answer 93

oDue to the bend of light by the atmosphere, it is not possible to measure angles smaller than 0.001arc sec on earth.
oThe means that distances greater than 100pc cannot be measured.

Question 94

Describe the apparent magnitude scale

Answer 94

Students should know that apparent magnitude depends on luminosity and the distance to a star. They should also know that a magnitude 1 star is 100 times brighter than a magnitude 6 star.

Question 95

Absolute magnitude

Answer 95

the magnitude of a star viewed from a distance of 10pc

Question 96

Outline the nature of a Cepheid variable

Answer 96

(Students should know that a Cepheid variable is a star in which the outer layers undergo a periodic expansion and contraction, which produces a periodic variation in its luminosity)
•For stars further away than 10Mpc the amount of light received is too small to accurately determine their temperature. In this case an alternative method is used that involves measuring the time period of a flashing star.
•A Cepheid variable is an unstable star that undergoes periodic expansions and contractions, leading to a periodic change in the apparent brightness of the star, as viewed from Earth.

Question 97

State the relationship between period and absolute magnitude for Cepheid variables

Answer 97

• The period and luminosity are related, proportional towards each other
• Cepheid variables may be used as “standard candles” to check other methods. If a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined by using the luminosity–period relationship.

Question 98

Explain how Cepheid variables may be used as “standard candles”

Answer 98

It is sufficient for students to know that, if a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined.

Question 99

Describe Newton´s model of the universe

Answer 99

Students should know that Newton assumed an infinite (in space and time), uniform and static universe.

Question 100

Explain Olbers´ paradox

Answer 100

Students should be able to show quantitatively, using the inverse square law of luminosity, that Newton´s model of the universe leads to a sky that should never be dark.

Question 101

How can we see that the universe is expanding?

Answer 101

the red-shift of light from galaxies indicate that the universe is expanding.

Question 102

Describe the discovery of cosmic microwave background (CMB) radiation be Penzias and Wilson

Answer 102

In 1965 they discovered that radiation was coming in all directions from space. The spectrum detected was typical of a black body at 3K… this is leftover heat from the Big Bang

Question 103

Explain how cosmic radiation in the microwave region is consistent with the Big Bang model

Answer 103

A simple explanation in terms of the universe “cooling down” is all that is required.

Question 104

Suggest how the Big Bang model provides a resolution to Olbers´ paradox

Answer 104

If the universe is not infinitely old, light from distant galaxies will not have reached us yet. (Also the universe is expanding)

Question 105

An open Universe

Answer 105

is one that continues to expand forever. The force of gravity slows the rate of recession of the galaxies
down a little bit but it is not strong enough to bring the expansion to a halt. A low density universe.

Question 106

A closed Universe

Answer 106

is one that is brought to a stop and then collapses back on itself ( “big crunch”). The force of gravity is enough to bring the expansion to an end. A high density universe.

Question 107

A flat Universe

Answer 107

is the mathematical possibility between open and closed. The force of gravity keeps on slowing the expansion down but it takes an infinite time to get to rest. This would only happen if universe were exactly the right density. One electron more, and the gravitational force would be a little bit bigger. Just enough to start the contraction and make the Universe closed

Question 108

Critical density

Answer 108

the theoretical value of the density that would create a flat universe

Question 109

Discuss how the density of the universe determines the development of the universe

Answer 109

• The density of the universe is not an easy quantity to measure.
• It is reasonable easy to estimate the mass in a galaxy by estimating the number of stars and their average mass.
• This estimation results in a galaxy mass which is too small.
• We know this because we can use mathematics of orbital motion to work out how much mass there must be keeping the outer stars in orbit around the galactic center

Question 110

Discuss an example of the international nature of recent astrophysics research

Answer 110

• The Cosmic Background Explorer (COBE) was launched on 18 November 1989. COBE determined that the CMB exhibits anisotropies at a level of one part in 105 and showed that the CMB spectrum matched that of a black body with a temperature of 2.725 K ± 2 mK.
• ESA’s 2009 Planck mission could answer some of the fundamental questions about the nature of dark matter. Its objective is to analyse, with the highest accuracy ever achieved, the remnants of radiation that filled the Universe immediately after the Big Bang.

Question 111

Describe the conditions that initiate fusion in stars

Answer 111

In order for any of these reactions to take place:

• two positively charged particles (hydrogen or helium nuclei) need to come close enough for interactions to take place. (Obviously they will repel one another)
• A high temperature.

Question 112

Outline the changes that take place in nucleosynthesis when a star leaves the main sequence and becomes a red giant

Answer 112

• It is fusion of hydrogen into helium and at some point hydrogen in the core will become rare.
• The fusion reactions will happen less often. This means that the star is no longer in equilibrium and the gravitational force will, once again, cause the core to collapse.
• This collapse increases the temperature of the core still further and helium fusion is now possible.
• The net result is for the star to increase massively in size – this expansion means that the outer layers are cooler. It becomes a red giant.
• This process of fusion as a source of energy must come to an end with the nucleosysthesis of iron.
• The iron nucleus has the greatest binding energy per nucleon of all nuclei.

Question 113

Compare the fate of red giant and super red supernova

Answer 113

• A red giant from a planetary nebula and then becomes a white dwarf
• A white dwarf is stable due to electron degeneracy pressure
• A red supergiant experiences a supernova and becomes a neuron star or collapse to a black hole
• A neuron star is stable due to neutron degeneracy pressure

Question 114

Outline the characteristics of pulsars

Answer 114

• Pulsars are rotating neutron stars emitting radio wave pulses.
• Neutron stars have strong magnetic fields.
• Magnetic fields accelerate charged particles, which release radiation.)
• This radiation can only be observed when the beam of emission is pointing toward the Earth, much the way a lighthouse can only be seen when the light is pointed in the direction of an observer, and is responsible for the pulsed appearance of emission.

Question 115

Explain the red-shift of light from distant galaxies

Answer 115

• Students should realize that the red-shift is due to the expansion of the universe.
• Doppler redshift is a phenomenon in which the visible light from an object is shifted towards the red end of the spectrum. It is an observed increase in the wavelength, which corresponds to a decrease in the frequency of electromagnetic radiation, received by a detector compared to that emitted by the source. The corresponding shift to shorter wavelengths is called blueshift.

Question 116

State Hubble´s law

Answer 116

the farther a galaxy, the faster it is receding from Earth. v=Hd

Question 117

Discuss the limitations of Hubble´s law

Answer 117

1. Distances to galaxies are difficult to measure..
2. It should be noted that, on very large scales, Einstein’s theory predicts departures from a strictly linear Hubble law.
3. … and nearby galaxies cannot be used to verify Hubble’s Law because they are more affected by gravitation that expansion.

Question 118

Explain how the expansion of the universe made possible the formation of light nuclei and atoms

Answer 118

Students should appreciate that, at the very high temperatures of the early universe, only elementary (fundamental) particles could exist and that expansion gave rise to cooling to temperatures at which light nuclei could be stable.

Question 119

A visual binary star

Answer 119

is a binary star for which the angular separation is great enough to permit them to be observed as a double star in a telescope. The resolving power of the telescope is an important factor in the detection of visual binaries, and as telescopes become larger and more powerful an increasing number of visual binaries will be detected. The brightness of the two stars is also an important factor, as brighter stars are harder to separate due to their glare than dimmer ones are.

Question 120

A spectroscopic binary star

Answer 120

is a binary star in which the separation between the stars is usually very small, and the orbital velocity very high. A Doppler shift occurs when they move towards/away from you so the spectrum regularly changes.

Question 121

An eclipsing binary star

Answer 121

is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. Eclipsing binaries are variable stars, not because the light of the individual components vary, but because of the eclipses.

Question 122

Parsec

Answer 122

the distance at which one Au subtends an angle of one second

Question 123

Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec

Answer 123

oDue to the bend of light by the atmosphere, it is not possible to measure angles smaller than 0.001arc sec on earth.
oThe means that distances greater than 100pc cannot be measured.

Question 124

Describe the apparent magnitude scale

Answer 124

Students should know that apparent magnitude depends on luminosity and the distance to a star. They should also know that a magnitude 1 star is 100 times brighter than a magnitude 6 star.

Question 125

Absolute magnitude

Answer 125

the magnitude of a star viewed from a distance of 10pc

Question 126

Outline the nature of a Cepheid variable

Answer 126

(Students should know that a Cepheid variable is a star in which the outer layers undergo a periodic expansion and contraction, which produces a periodic variation in its luminosity)
•For stars further away than 10Mpc the amount of light received is too small to accurately determine their temperature. In this case an alternative method is used that involves measuring the time period of a flashing star.
•A Cepheid variable is an unstable star that undergoes periodic expansions and contractions, leading to a periodic change in the apparent brightness of the star, as viewed from Earth.

Question 127

State the relationship between period and absolute magnitude for Cepheid variables

Answer 127

• The period and luminosity are related, proportional towards each other
• Cepheid variables may be used as “standard candles” to check other methods. If a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined by using the luminosity–period relationship.

Question 128

Explain how Cepheid variables may be used as “standard candles”

Answer 128

It is sufficient for students to know that, if a Cepheid variable is located in a particular galaxy, then the distance to the galaxy may be determined.

Question 129

Describe Newton´s model of the universe

Answer 129

Students should know that Newton assumed an infinite (in space and time), uniform and static universe.

Question 130

Explain Olbers´ paradox

Answer 130

Students should be able to show quantitatively, using the inverse square law of luminosity, that Newton´s model of the universe leads to a sky that should never be dark.

Question 131

How can we see that the universe is expanding?

Answer 131

the red-shift of light from galaxies indicate that the universe is expanding.

Question 132

Describe the discovery of cosmic microwave background (CMB) radiation be Penzias and Wilson

Answer 132

In 1965 they discovered that radiation was coming in all directions from space. The spectrum detected was typical of a black body at 3K… this is leftover heat from the Big Bang

Question 133

Explain how cosmic radiation in the microwave region is consistent with the Big Bang model

Answer 133

A simple explanation in terms of the universe “cooling down” is all that is required.

Question 134

Suggest how the Big Bang model provides a resolution to Olbers´ paradox

Answer 134

If the universe is not infinitely old, light from distant galaxies will not have reached us yet. (Also the universe is expanding)

Question 135

An open Universe

Answer 135

is one that continues to expand forever. The force of gravity slows the rate of recession of the galaxies
down a little bit but it is not strong enough to bring the expansion to a halt. A low density universe.

Question 136

A closed Universe

Answer 136

is one that is brought to a stop and then collapses back on itself ( “big crunch”). The force of gravity is enough to bring the expansion to an end. A high density universe.

Question 137

A flat Universe

Answer 137

is the mathematical possibility between open and closed. The force of gravity keeps on slowing the expansion down but it takes an infinite time to get to rest. This would only happen if universe were exactly the right density. One electron more, and the gravitational force would be a little bit bigger. Just enough to start the contraction and make the Universe closed

Question 138

Critical density

Answer 138

the theoretical value of the density that would create a flat universe

Question 139

Discuss how the density of the universe determines the development of the universe

Answer 139

• The density of the universe is not an easy quantity to measure.
• It is reasonable easy to estimate the mass in a galaxy by estimating the number of stars and their average mass.
• This estimation results in a galaxy mass which is too small.
• We know this because we can use mathematics of orbital motion to work out how much mass there must be keeping the outer stars in orbit around the galactic center

Question 140

Discuss an example of the international nature of recent astrophysics research

Answer 140

• The Cosmic Background Explorer (COBE) was launched on 18 November 1989. COBE determined that the CMB exhibits anisotropies at a level of one part in 105 and showed that the CMB spectrum matched that of a black body with a temperature of 2.725 K ± 2 mK.
• ESA’s 2009 Planck mission could answer some of the fundamental questions about the nature of dark matter. Its objective is to analyse, with the highest accuracy ever achieved, the remnants of radiation that filled the Universe immediately after the Big Bang.

Question 141

Describe the conditions that initiate fusion in stars

Answer 141

In order for any of these reactions to take place:

• two positively charged particles (hydrogen or helium nuclei) need to come close enough for interactions to take place. (Obviously they will repel one another)
• A high temperature.

Question 142

Outline the changes that take place in nucleosynthesis when a star leaves the main sequence and becomes a red giant

Answer 142

• It is fusion of hydrogen into helium and at some point hydrogen in the core will become rare.
• The fusion reactions will happen less often. This means that the star is no longer in equilibrium and the gravitational force will, once again, cause the core to collapse.
• This collapse increases the temperature of the core still further and helium fusion is now possible.
• The net result is for the star to increase massively in size – this expansion means that the outer layers are cooler. It becomes a red giant.
• This process of fusion as a source of energy must come to an end with the nucleosysthesis of iron.
• The iron nucleus has the greatest binding energy per nucleon of all nuclei.

Question 143

Compare the fate of red giant and super red supernova

Answer 143

• A red giant from a planetary nebula and then becomes a white dwarf
• A white dwarf is stable due to electron degeneracy pressure
• A red supergiant experiences a supernova and becomes a neuron star or collapse to a black hole
• A neuron star is stable due to neutron degeneracy pressure

Question 144

Outline the characteristics of pulsars

Answer 144

• Pulsars are rotating neutron stars emitting radio wave pulses.
• Neutron stars have strong magnetic fields.
• Magnetic fields accelerate charged particles, which release radiation.)
• This radiation can only be observed when the beam of emission is pointing toward the Earth, much the way a lighthouse can only be seen when the light is pointed in the direction of an observer, and is responsible for the pulsed appearance of emission.

Question 145

Explain the red-shift of light from distant galaxies

Answer 145

• Students should realize that the red-shift is due to the expansion of the universe.
• Doppler redshift is a phenomenon in which the visible light from an object is shifted towards the red end of the spectrum. It is an observed increase in the wavelength, which corresponds to a decrease in the frequency of electromagnetic radiation, received by a detector compared to that emitted by the source. The corresponding shift to shorter wavelengths is called blueshift.

Question 146

State Hubble´s law

Answer 146

the farther a galaxy, the faster it is receding from Earth. v=Hd

Question 147

Discuss the limitations of Hubble´s law

Answer 147

1. Distances to galaxies are difficult to measure..
2. It should be noted that, on very large scales, Einstein’s theory predicts departures from a strictly linear Hubble law.
3. … and nearby galaxies cannot be used to verify Hubble’s Law because they are more affected by gravitation that expansion.

Question 148

Explain how the expansion of the universe made possible the formation of light nuclei and atoms

Answer 148

Students should appreciate that, at the very high temperatures of the early universe, only elementary (fundamental) particles could exist and that expansion gave rise to cooling to temperatures at which light nuclei could be stable.