1
Q
what happens to a light source as you get further away?
A
Light source appear fainter at greater distances because the emitted light spreads over a larger area as it travels
2
Q
What is the surface area of a sphere, and how does it relate to the distance of a star?
A
the surface area is 4xpixr^2, where r is the radius.
For a star, the radius is the distance between the star and earth
3
Q
how is the radiation recieved at earth
A
the radiation is spread out equally through the area of 4 x pi x d^2
4
Q
what is the equation for the inverse square law of flux?
A
F = L
————-
4xpixd^2
F= flux (intensity) (wm^-2)
L= Luminosity (w)
d= distance between the star and earth (m)
5
Q
what are the assumptions does the inverse square law make?
A
- the power from a star radiates uniformly through space
- No radiation is absorbed between the star and the earth
6
Q
what does this equation tell us
A
This equation tells us:
For a given star, the luminosity is constant
The radiant flux follows an inverse square law
The greater the radiant flux (larger F) measured, the closer the star is to the Earth (smaller d)
7
Q
what is the principle of parrallax
A
it is based on how the position of an object appears to change as the position of observer changes
8
Q
what is an example of parallex and what is it used for
A
stellar parallex
- can be used to measure the distance of nearby stars
9
Q
what is the definition of stellar parallex
A
the apparent shifting in position of a nearby star against a background of distant stars when viewed from different positions of the earth during the earths orbit about the sun
10
Q
what does stellar parallax involve
A
how the position of a nearby star changes over a period of time against a fixed background of distant stars
- from the observes position the distant stars dont appear to move
- this difference is creates the effect of stellar parralex
11
Q
what is 1 AU and what is the value
A
it is the radius of the earths orbit around the sun it is 150,000,000 km
12
Q
how do they use stellar parallax on earth to obseve distance to stars
A
The observations are made six months apart to maximise the distance the Earth has moved from its starting position
The Earth has completed half a full orbit and is at a different position in its orbit around the Sun
The nearby star will appear in different positions against a backdrop of distant stars which will appear to not have moved
This apparent movement of the nearby star is called the stellar parallax
13
Q
what is the stellar parralax equation
A
tan p = AU
—–
d
For small angles, expressed in radians tan p = p
so
p= AU/d
14
Q
definition of an arcsecond
A
it is 1/3600 degrees
15
Q
definition of arc minute
A
1/60 degrees
16
Q
how do arcsecond and parsecs relate
A
(parsec) d = 1/p (arcsec)
17
Q
definition of a parsec
A
A parsec is the distance at which an object has a parallax angle of 1 arcsecond when observed from opposite sides of Earth’s orbit, separated by 1 astronomical unit (AU)
18
Q
what is the value of 1 parsec
A
3.1 x 10^16m
19
Q
what is 1 light year = to
A
9.5 x 10^15m
20
Q
what is the definition of a standard candle
A
An astronomical object which has a known luminosity due to a characteristic quality possessed by that class of object
21
Q
what are the two types of standard candles are
A
cepheid variable stars
Type 1a supernova
22
Q
definition of apparent magnitude
A
how bright a star appears from our viewpoint
23
Q
definition of absolute magnitude
A
how bright a star is from from a fixed distance of 10pc
24
Q
what is the max distance you can use stellar parralex
A
1000 parsecs
25
what is the type 1a supernova and why does it mean you can find the distance
A supernova explosion involving a white dwarf
The luminosity at the time of the explosion is always the same
26
what is a cephied variable star
A type of pulsating star which increases and decreases in brightness over a set time period
This variation has a well defined relationship to the luminosity
27
what is the advantage of using standing candles to measure distance
there is no distance limit as you can measure the period no matter how far you are
28
whats the period equation in terms of distance
................ _________
t = 2 x pi / r^3
/--------------
/ Gx M
29
What is the luminosity of a star?
Luminosity is the total energy a star emits per second in all directions, measured in watts.
30
What does the luminosity depend on?
1. Surface area (4 pi r^2) - larger starts emit more energy
2. Surface temperature - hotter stars radiate more energy according to the stefan-boltzmann law
31
What is the UV Catastrophe?
Classical theory predicted an infinite amount of energy as wavelength approached zero, which contradicted experimental data. where there is a drop at the ultra violet level.
32
how does the uv catastrophe work?
At higher frequencies the energy of each
hf) becomes larger.
A system is less likely to have enough energy to produce these high-energy quanta.
This reduces the number of high-frequency photons emitted, causing the intensity to drop.
33
what is wiens law
wavelength is inversely proportional to the absolute temperature
34
what is wiens equation
lamba(peak) x T(emperature) = 2.898 x 10^-3 mk
35
what is wiens constant
- 2.898 x 10^-3 mk
36
what is preferential scattering
preferential scattering (refraction) of Blue light (sky is blue) leaves yellow as the dominant colour we see from the disc
37
what is the stefan boltzmann law
the relationship between surface temp and luminosity
L proportional T^4
also
L proportional to Area
so therefore
L= sigma x 4xpixr^2xT^4
38
what is stefan boltzmanns constant
5.67 x 10^-8 Wm^-2K^-4
39
what is the stellar cycle (small main sequence) ?
1. star forming nebula
2.protostar
3.yellow star
4. red giant
5. planetary nebula
6. white dwarf
7. Black Dwarf
40
what is the stellar cycle (Large main sequence) ?
1. star forming nebula
2. protostar
3. Blue Giant
4. Red supergiant
5. super nova
if massive
- Black hole
if just large
- neutron star
41
what happens in a star forming nebula?
- it is a giant cloud of hydrogen gas and dust
- gravitational attraction between atoms cause denser dumps of matter (gravitational collapse)
42
what happens when it goes from a nebula to a yellow star?
Nuclear fusion
- eventually temp reaches millions of Kelvin and the fusion of hydrogen to helium begins
43
explain the process from a nebula to a protostar
Gravitational forces cause regions of a molecular cloud (nebula) to collapse, forming dense clumps.
As the clumps contract, they heat up due to gravitational energy converting into thermal energy.
A central dense object forms, called a protostar.
The protostar’s radiation pressure begins to resist further collapse but isn’t sufficient to start fusion yet.
44
explain the process from a nebula to a protostar
The protostar continues contracting and heating until the core temperature reaches ~10 million K.
The star achieves hydrostatic equilibrium: radiation pressure balances gravitational forces.
The star is now a main sequence star, where it remains for most of its life, converting hydrogen into helium.
Position on the Hertzsprung-Russell (H-R) diagram depends on mass (higher mass = hotter and more luminous).
45
explain the process of a man sequence star to a red giant to a red supergiant
Hydrogen in the core is depleted, and fusion ceases there.
The core contracts and heats, while hydrogen fusion continues in a shell around the core.
Increased radiation pressure causes the outer layers to expand and cool, forming a red giant (low-mass stars) or red supergiant (high-mass stars).
46
explain the process of a red giant to a planetary nebula and a white dwarf
In the core, helium nuclei fuse into carbon and oxygen via the triple-alpha process.
Once helium is exhausted, the core cannot sustain fusion of heavier elements.
The outer layers are ejected, forming a glowing planetary nebula.
The hot, dense core becomes a white dwarf, supported by electron degeneracy pressure.
47
explain the process of a White Dwarf to Black Dwarf
A white dwarf radiates away its residual heat over billions of years, gradually cooling and dimming.
Eventually, it becomes a black dwarf, a theoretical end-state (not yet observed as the universe is not old enough).
48
explain the process of a red supergiant to Supernova and Neutron Star (High-Mass Stars)
Successive fusion shells form heavier elements up to iron, which cannot release energy through fusion.
The core collapses under gravity, triggering a Type II supernova.
The remnant core becomes a neutron star, supported by neutron degeneracy pressure.
Neutron stars are incredibly dense, with a radius of ~10 km, and may appear as pulsars if their magnetic field and spin align to produce detectable radiation.
49
explain the process of a Red Supergiant to Supernova and Black Hole (Very High-Mass Stars)
Similar to neutron star formation, but if the core remnant exceeds the Tolman-Oppenheimer-Volkoff limit (~3 solar masses), gravity overcomes all forms of degeneracy pressure.
The core collapses completely, forming a black hole.
A black hole is characterized by an event horizon, the boundary beyond which no light or matter can escape.
For A-Level Physics, understand that the black hole’s mass and escape velocity define this limit, but calculations of event horizon radius are beyond the scope.
50
what is the effect of a super nova and its link to a nebula
A supernova explosion ejects outer layers into space, enriching the interstellar medium with heavy elements.
These materials contribute to the formation of new stars, planets, and nebulae, restarting the stellar cycle.
The leftover core remnant may form a neutron star or black hole, depending on its mass.
51
what does the hertzsprung - russel diagram show
luminosity of different stars against their temperature
Luminosity relative to the Sun, on the y-axis, goes from dim (at the bottom) to bright (at the top)
Temperature in degrees kelvin, on the x-axis, goes from hot (on the left) to cool (on the right)
52
what does the Hertzsprung and Russel diagram show
Most stars are clustered in a band called the main sequence
For main sequence stars, luminosity increases with surface temperature
A smaller number of stars clustered above the main sequence in two areas, red giants, and red super giants
These stars show an increase in luminosity at cooler temperatures
The only explanation for this is that these stars are much larger than main sequence stars
Below and to the left of the main sequence are the white dwarf stars
These stars are hot, but not very luminous
Therefore, they must be much smaller than main sequence stars
53
what does the Hertzsprung-Russell Diagram not show
it only shows stars in stable phase
Transitory phases happen quickly in relation to the lifetime of a star
Black holes cannot be seen since they emit no light
54
what is the definition of the astronomical unit
1 AU is the mean distance between the Earth and the Sun
55
the definition of the doppler effect
the doppler effect is the apparent change of wavelength as a result of relative movement between a receiver and source
56
how does the doppler effect relate to red shift
red shift is the change in frequency as a light source moves further away, the doppler effect is the same but with light
57
How is frequency interpreted in red shift and doppler effect?
In the Doppler effect, the frequency is referred to as the pitch, whereas for light it is interpreted as the colour
58
what remains constant in the doppler effect and what changes
velocity is fixed, so if frequency increases, the wavelength goes down
59
what is the equation for the doppler effect
f'= ( Vwave )
( ------------------ ) xf
( Vwave+Vsource )
60
what happens to the observed wavelength of a wave source moving away from the observer
the observed wavelength will increase
61
what happens to the observed wavelength of a wave source moving towards from the observer
the observed wavelength will decrease
62
what happens to the observed frequency of a wave source moving towards from the observer
the observed frequency will increase
63
definition of red shift
red shift is the apparent shift of the wavelength of light emitted by a star towards the red end of the light spectrum, as a result of it receding
64
what are the equations for red shift
z (red shift value) = Change in Lamba
--------------------------
lamba
or
change in frequency
--------------------------------
frequency
or
change in velocity
---------------------------
speed of light
65
how does the relative speed value inputted into the equation differs depending on if the source is coming near or moving away
if the source and receiver are approaching each other, the value should be negative, otherwise the value is positive
66
whats the difference between a positive and negative z value?
a positive z value represents red shift, a negative value represents blue shift
67
what are the two main conclusions that can be drawn from observation of red shift from distant galaxies?
1. all galaxies show red shift and so all galaxies are moving away
2. the more distant a galaxy is, the greater its red shift and so the faster it is receding
68
what does the red shift of distant galaxies provide evidence for ?
red shift of distant galaxies suggest they are moving away from us. this supports the concept that the universe is expanding which supports the big bang theory
69
why are there lines of darkness in the spectroscope of the sun?
The sun produces almost all the colors. The little black lines are called absorption lines, and they occur because the gas in the sun's atmosphere doesn't let all the light out; it absorbs some. We know where these lines should be. They correspond to the wavelengths absorbed by hydrogen and helium atoms in the sun.
70
what is the proof of redshift.
If we look at light from distant galaxies, all the little lines should be in the same place, as hydrogen and helium are the same everywhere. This proves redshift, as there are the same lines just shifted towards the red end of the spectrum.
71
what is blue shift.
the same as red shift but towords the blue side as the object is moving closer.
72
what does CMBR stand for
Cosmic microwave Background radiation
73
what is cosmic background radiation
Radiation in the microwave region of the Em spectrum that is present in very small quantities all around us
74
how does CMBR support the Big Bang theory
During the Big Bang, a significant amount of high-energy radiation was produced. As the universe expanded over time, the wavelength of this radiation stretched, placing it in the microwave region. Other theories of the universe cannot account for the existence of the Cosmic Microwave Background Radiation (CMBR).
75
what is the big bang theory
the big bang theory is a theory for the formation of the universe. It proposes that the universe began from a very small, hot and dense region, and expanded from this point
76
what two quantities does the hubbles law relate
the distance of a galaxy to the speed at which it is moving away
77
express hubbles law in words
the speed at which a galaxy is moving away, is directly proportional to the distance it is at
78
state the defining equation for Hubbles Law
velocity (v) = Ho (hubbles consant) x distance
79
describe what was observed when observations of galaxies brightness were compared to the prediction made by hubbles law
- TThe actual and predicted brightnesses of distant galaxies do not always agree with each other. Distant galaxies are not as bright as predicted by Hubble's law, suggesting that they are more distant than anticipated.
80
state the conclusion that can be made from hubbles law and observations
the rate of expansion of the universe is acceleration, since galaxies are further away than predicted
81
Give one possible explanation for the acceleration of the universes expansion
The existence of Dark energy. This would explain where the energy required for the expansion rate to constantly accelerate comes from
82
why is the existence of dark energy still only a hypothesis
Dark matter and energy cant easily be observed
83
what is the value for hubble constant
67.4 +- 0.5 km s^-1Mpc^-2
84
what would we expect to happen as objects move away from us
for there velocity to decrease as there is a weakening of gravitational field strength
this happens for small objects like solar systems (furthest planets orbit the slowest) but not large objects like galaxies
85
defintion of dark matter
dark matter is defined as matter which cannot be seen and that does not emit or absorb em radiation
86
how can we detect dark matter?
we can detect it through telescopes
It should make up 85 percent of the mass in the universe
it is detected based on its gravitational effects relation to the rotation of other galaxies.
87
whats the order of spectral class and there simular temperature
05 50,000k
B0 30,000k
A0 10,000k
F0 7000 k
G0 6000k
K0 5000k
M0 3000k
88
what is dark energy
The universe is constantly expanding and accelerating. energy is needed to accelerate something. therefore we call this energy dark energy.
