Option E: astrophysics Flashcards
1
Q
Stellar cluster
A
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.
2
Q
Constellation
A
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.
3
Q
light year
A
This is equal to the distance travelled by light in one year
4
Q
the luminosity of a star
A
The total amount of energy emitted by the star per second
5
Q
Apparent brightness
A
the amount of energy per second received per unit area
6
Q
Wien´s law
A
The relationship between the peak wavelength on the graph of Stephan-Boltzmann graph and the temperature is given by Wien displacement graph.
7
Q
Explain how atomic spectra may be used to deduce chemical and physical data for stars
A
- To put it simply, spectra reveal the presence of elements, ions, and molecules.
- Spectra indicate temperature of the object.
- Spectra indicate doppler motion of the object.
8
Q
binary stars
A
A binary star is a stellar system consisting of two stars orbiting around their center of mass
9
Q
red giants
A
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
10
Q
white dwarfs
A
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.
11
Q
A visual binary star
A
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.
12
Q
A spectroscopic binary star
A
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.
13
Q
An eclipsing binary star
A
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.
14
Q
Parsec
A
the distance at which one Au subtends an angle of one second
15
Q
Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec
A
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.
16
Q
Describe the apparent magnitude scale
A
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.
17
Q
Absolute magnitude
A
the magnitude of a star viewed from a distance of 10pc
18
Q
Outline the nature of a Cepheid variable
A
(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.
19
Q
State the relationship between period and absolute magnitude for Cepheid variables
A
- 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.
20
Q
Explain how Cepheid variables may be used as “standard candles”
A
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.
21
Q
Describe Newton´s model of the universe
A
Students should know that Newton assumed an infinite (in space and time), uniform and static universe.
22
Q
Explain Olbers´ paradox
A
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.
23
Q
How can we see that the universe is expanding?
A
the red-shift of light from galaxies indicate that the universe is expanding.
24
Q
A visual binary star
A
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.
25
A spectroscopic binary star
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.
26
An eclipsing binary star
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.
27
Parsec
the distance at which one Au subtends an angle of one second
28
Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec
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.
29
Describe the apparent magnitude scale
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.
30
Absolute magnitude
the magnitude of a star viewed from a distance of 10pc
31
Outline the nature of a Cepheid variable
(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.
32
State the relationship between period and absolute magnitude for Cepheid variables
* 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.
33
Explain how Cepheid variables may be used as “standard candles”
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.
34
Describe Newton´s model of the universe
Students should know that Newton assumed an infinite (in space and time), uniform and static universe.
35
Explain Olbers´ paradox
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.
36
How can we see that the universe is expanding?
the red-shift of light from galaxies indicate that the universe is expanding.
37
A visual binary star
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.
38
A spectroscopic binary star
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.
39
An eclipsing binary star
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.
40
Parsec
the distance at which one Au subtends an angle of one second
41
Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec
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.
42
Describe the apparent magnitude scale
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.
43
Absolute magnitude
the magnitude of a star viewed from a distance of 10pc
44
Outline the nature of a Cepheid variable
(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.
45
State the relationship between period and absolute magnitude for Cepheid variables
* 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.
46
Explain how Cepheid variables may be used as “standard candles”
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.
47
Describe Newton´s model of the universe
Students should know that Newton assumed an infinite (in space and time), uniform and static universe.
48
Explain Olbers´ paradox
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.
49
How can we see that the universe is expanding?
the red-shift of light from galaxies indicate that the universe is expanding.
50
A visual binary star
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.
50
A visual binary star
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.
51
A spectroscopic binary star
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.
51
A spectroscopic binary star
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.
52
An eclipsing binary star
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.
52
An eclipsing binary star
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.
53
Parsec
the distance at which one Au subtends an angle of one second
53
Parsec
the distance at which one Au subtends an angle of one second
54
Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec
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.
54
Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec
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.
55
Describe the apparent magnitude scale
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.
55
Describe the apparent magnitude scale
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.
56
Absolute magnitude
the magnitude of a star viewed from a distance of 10pc
56
Absolute magnitude
the magnitude of a star viewed from a distance of 10pc
57
Outline the nature of a Cepheid variable
(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.
57
Outline the nature of a Cepheid variable
(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.
58
State the relationship between period and absolute magnitude for Cepheid variables
* 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.
58
State the relationship between period and absolute magnitude for Cepheid variables
* 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.
59
Explain how Cepheid variables may be used as “standard candles”
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.
59
Explain how Cepheid variables may be used as “standard candles”
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.
60
Describe Newton´s model of the universe
Students should know that Newton assumed an infinite (in space and time), uniform and static universe.
60
Describe Newton´s model of the universe
Students should know that Newton assumed an infinite (in space and time), uniform and static universe.
61
Explain Olbers´ paradox
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.
61
Explain Olbers´ paradox
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.
62
How can we see that the universe is expanding?
the red-shift of light from galaxies indicate that the universe is expanding.
62
How can we see that the universe is expanding?
the red-shift of light from galaxies indicate that the universe is expanding.
63
A visual binary star
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.
63
A visual binary star
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.
64
A spectroscopic binary star
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.
64
A spectroscopic binary star
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.
65
An eclipsing binary star
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.
65
An eclipsing binary star
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.
66
Parsec
the distance at which one Au subtends an angle of one second
66
Parsec
the distance at which one Au subtends an angle of one second
67
Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec
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.
67
Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec
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.
68
Describe the apparent magnitude scale
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.
68
Describe the apparent magnitude scale
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.
69
Absolute magnitude
the magnitude of a star viewed from a distance of 10pc
69
Absolute magnitude
the magnitude of a star viewed from a distance of 10pc
70
Outline the nature of a Cepheid variable
(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.
70
Outline the nature of a Cepheid variable
(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.
71
State the relationship between period and absolute magnitude for Cepheid variables
* 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.
71
State the relationship between period and absolute magnitude for Cepheid variables
* 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.
72
Explain how Cepheid variables may be used as “standard candles”
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.
72
Explain how Cepheid variables may be used as “standard candles”
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.
73
Describe Newton´s model of the universe
Students should know that Newton assumed an infinite (in space and time), uniform and static universe.
73
Describe Newton´s model of the universe
Students should know that Newton assumed an infinite (in space and time), uniform and static universe.
74
Explain Olbers´ paradox
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.
74
Explain Olbers´ paradox
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.
75
How can we see that the universe is expanding?
the red-shift of light from galaxies indicate that the universe is expanding.
75
How can we see that the universe is expanding?
the red-shift of light from galaxies indicate that the universe is expanding.
76
A visual binary star
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.
77
A spectroscopic binary star
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.
78
An eclipsing binary star
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.
79
Parsec
the distance at which one Au subtends an angle of one second
80
Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec
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.
81
Describe the apparent magnitude scale
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.
82
Absolute magnitude
the magnitude of a star viewed from a distance of 10pc
83
Outline the nature of a Cepheid variable
(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.
84
State the relationship between period and absolute magnitude for Cepheid variables
* 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.
85
Explain how Cepheid variables may be used as “standard candles”
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.
86
Describe Newton´s model of the universe
Students should know that Newton assumed an infinite (in space and time), uniform and static universe.
87
Explain Olbers´ paradox
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.
88
How can we see that the universe is expanding?
the red-shift of light from galaxies indicate that the universe is expanding.
89
A visual binary star
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.
90
A spectroscopic binary star
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.
91
An eclipsing binary star
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.
92
Parsec
the distance at which one Au subtends an angle of one second
93
Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec
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.
94
Describe the apparent magnitude scale
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.
95
Absolute magnitude
the magnitude of a star viewed from a distance of 10pc
96
Outline the nature of a Cepheid variable
(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.
97
State the relationship between period and absolute magnitude for Cepheid variables
* 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.
98
Explain how Cepheid variables may be used as “standard candles”
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.
99
Describe Newton´s model of the universe
Students should know that Newton assumed an infinite (in space and time), uniform and static universe.
100
Explain Olbers´ paradox
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.
101
How can we see that the universe is expanding?
the red-shift of light from galaxies indicate that the universe is expanding.
102
Describe the discovery of cosmic microwave background (CMB) radiation be Penzias and Wilson
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
103
Explain how cosmic radiation in the microwave region is consistent with the Big Bang model
A simple explanation in terms of the universe “cooling down” is all that is required.
104
Suggest how the Big Bang model provides a resolution to Olbers´ paradox
If the universe is not infinitely old, light from distant galaxies will not have reached us yet. (Also the universe is expanding)
105
An open Universe
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.
106
A closed Universe
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.
107
A flat Universe
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
108
Critical density
the theoretical value of the density that would create a flat universe
109
Discuss how the density of the universe determines the development of the universe
- 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
110
Discuss an example of the international nature of recent astrophysics research
- 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.
111
Describe the conditions that initiate fusion in stars
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.
112
Outline the changes that take place in nucleosynthesis when a star leaves the main sequence and becomes a red giant
* 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.
113
Compare the fate of red giant and super red supernova
* 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
114
Outline the characteristics of pulsars
- 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.
115
Explain the red-shift of light from distant galaxies
- 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.
116
State Hubble´s law
the farther a galaxy, the faster it is receding from Earth. v=Hd
117
Discuss the limitations of Hubble´s law
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.
118
Explain how the expansion of the universe made possible the formation of light nuclei and atoms
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.
119
A visual binary star
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.
120
A spectroscopic binary star
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.
121
An eclipsing binary star
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.
122
Parsec
the distance at which one Au subtends an angle of one second
123
Explain why the method of stellar parallax is limited to measure stellar distances less than several hundred parsec
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.
124
Describe the apparent magnitude scale
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.
125
Absolute magnitude
the magnitude of a star viewed from a distance of 10pc
126
Outline the nature of a Cepheid variable
(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.
127
State the relationship between period and absolute magnitude for Cepheid variables
* 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.
128
Explain how Cepheid variables may be used as “standard candles”
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.
129
Describe Newton´s model of the universe
Students should know that Newton assumed an infinite (in space and time), uniform and static universe.
130
Explain Olbers´ paradox
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.
131
How can we see that the universe is expanding?
the red-shift of light from galaxies indicate that the universe is expanding.
132
Describe the discovery of cosmic microwave background (CMB) radiation be Penzias and Wilson
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
133
Explain how cosmic radiation in the microwave region is consistent with the Big Bang model
A simple explanation in terms of the universe “cooling down” is all that is required.
134
Suggest how the Big Bang model provides a resolution to Olbers´ paradox
If the universe is not infinitely old, light from distant galaxies will not have reached us yet. (Also the universe is expanding)
135
An open Universe
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.
136
A closed Universe
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.
137
A flat Universe
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
138
Critical density
the theoretical value of the density that would create a flat universe
139
Discuss how the density of the universe determines the development of the universe
- 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
140
Discuss an example of the international nature of recent astrophysics research
- 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.
141
Describe the conditions that initiate fusion in stars
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.
142
Outline the changes that take place in nucleosynthesis when a star leaves the main sequence and becomes a red giant
* 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.
143
Compare the fate of red giant and super red supernova
* 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
144
Outline the characteristics of pulsars
- 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.
145
Explain the red-shift of light from distant galaxies
- 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.
146
State Hubble´s law
the farther a galaxy, the faster it is receding from Earth. v=Hd
147
Discuss the limitations of Hubble´s law
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.
148
Explain how the expansion of the universe made possible the formation of light nuclei and atoms
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.
