6. Space physics Flashcards
1
Q
What happens during nuclear fusion?
A
Small nuclei fuse together to form larger nuclei
Energy is released and a neutron
2
Q
Is fusion the energy source for stars?
A
Yes
3
Q
What are the similarities between fusion and fission?
A
both release neutrons
collisions involved
release energy
begin with daughter nuclei
4
Q
What are differences between fusion and fission?
A
fission can cause a chain reaction
fusion occurs in stars
fusion is when two nuclei collide, fission is when a nucleus splits
different numbers of neutrons are released (fusion releases only 1 neutron)
fusion is with small nuclei + fission is with large ones
5
Q
Why is it difficult to fuse two nuclei together?
A
nuclei are positively charged
6
Q
What are the conditions required for nuclear fusion?
A
high temps and high pressures
this mean that the nuclei are moving fast enough to ->
to overcome repulsive forces between (positive) nuclei + force them together
7
Q
What are the energy transfers in fusion?
A
energy radiated away from stars is stored as nuclear energy of protons and nuclei in the star
nuclear fusion transfers this into kinetic energy of nuclei (and transferred by radiation)
8
Q
What is a universe?
A
Large collection of billions of galaxies
9
Q
What is a galaxy?
A
Large collection of billions of stars
10
Q
What galaxy is our solar system within?
A
Milky Way
11
Q
What are asteroids?
A
small pieces of rocks which orbit the sun between mars and jupiter
12
Q
What are comets?
A
Rock / ice / methane / ammonia a few km in diameter
Orbit the sun in highly eccentric ellipses
13
Q
What are comets?
A
Rock / ice / methane / ammonia a few km in diameter
Orbit the sun in highly eccentric ellipses
14
Q
What do gravitational forces do?
A
cause moons to orbit planets
planets to orbit sun
causes artificial satellites to orbit earth
causes comets to orbit the sun
gravitational force keeps them moving in curved paths (orbits)
15
Q
Why do comets travel faster when they are closer to the sun?
A
Gravitational forces are larger when the objects are closer
Farther away from sun - maximum GPE and lower KE
Closer to sun- lower GPE and maximum KE
16
Q
Describe the differences in the orbits of comets moons and planets?
A
comets have highly elliptical orbits around the sun
moons have circular orbits
planets have slightly elliptical orbits
17
Q
What is the orbital speed equation?
A
Orbital speed = circumference (distance travelled) /orbital period (time to orbit once)
Orbital speed=
2π r (radius is distance from planet to sun) /T
18
Q
How to convert years to hours?
A
365 x 24 = 8760 hours
19
Q
What is meant by spectral class?
A
letter label given to a star
- relates to its colour and temp
20
Q
Recite the letters of spectral class, from hottest to coldest
A
Only
Bats
And
Flies
Go
Kicking
Mice
21
Q
What colour is the spectral class O and B?
A
Blue
22
Q
What colour is the spectral class A and F?
A
Blue white
White
23
Q
What colour is the spectral class G?
A
Yellow white
24
Q
What colour is the spectral class K?
A
Orange
25
What colour is the spectral class M?
Red
26
Describe the evolution of stars of similar mass to the sun through the following stages:
nebula
star (main sequence)
NEBULA
1. Nebula collapses (dust + gas fall toward centre of mass due to gravitational attraction)
2. GPE -> KE + THERMAL ENERGY of the gas (thus temp increases)
3. Protostar forms at centre (planets form in disk surrounding it)
4. temp in protostar continues to increase until hot enough for nuclear fusion to occur, now main sequence star
MAIN SEQUENCE (stable)
1. When size is not changing= stable
2. Gravitational forces (trying to make star collapse) and thermal pressures (trying to make star expand) are in equilibrium
27
Describe the evolution of stars of similar mass to the sun through the following stages:
red giant
white dwarf
RED GIANT
1. Runs out of hydrogen -> OuTER SHELL gravitationally collapses, (as gravitational force bigger than thermal pressures) increasing the temp
2. Eventually hot enough for helium fusion to occur - increases temp further -> star expands to become a red giant (red because surface area so large, cooler than before) fusion of heavier elements becomes possible as temp increases
WHITE DWARF
1. Star expands rapidly due to increase in temp (caused by fusion of heavier elements) gravity not strong enough to keep star together -> outer layers of star are ejected (left with core of the star)
2. Star core compresses until it becomes very small hot white dwarf
3. Eventually becomes black dwarf when it radiates all of its energy
28
Do high or low mass stars have a larger lifetime? Why?
Low mass as fusion occurs more slowly (not as hot)
29
Describe the evolution of stars with a mass larger than the sun?
Red SUper giant and supernova
RED SUPER GIANT
1. After stable period, larger mass stars expand into red supergiants
2. Fusion can occur up to creation of iron.
SUPERNOVA
3. Runs out of nuclear fuel -> rapid collapse of star (temperature decreases, gravitational forces overcome outward pressure)
4. Followed by an explosion (enough GPE transferred to fuse elements heavier than iron)
5. Material ejected by supernova spreads out into space in a nebula (where more stars are born - these with heavier elements)
30
Scientists believe that the universe began in the Big Bang. It predicts that most of the universe would be hydrogen with small amounts of heavier elements. Explain where the other elements were created?
Elements < iron but > hydrogen occurred in centre of stars by fusion
Energy released in supernova enough to create elements > iron
31
Describe the evolution of stars with a mass larger than the sun. Neutron star and black holes
NEUTRON STARS
one remnant of supernova = neutron star = small and dense
Black holes
if remnant is greater than 2.5 solar masses a black hole remains
black hole so dense that light cannot escape its gravitational field
32
Describe large mass main sequence stars
Hot
White + blue
Fusion occurs quickly
Relatively short lifetime
33
Low mass main sequence stars
Cool
Red
Fusion occurs slowly
Large lifetime
34
What is apparent magnitude?
Brightness of a star
depends on : luminosity (how much energy it radiates) + distance from Earth
very bright = small/negative apparent magnitudes
very dim = high apparent magnitudes
35
What is absolute magnitude?
allows us to compare brightness of stars -> measure of how bright they would appear if all same distance from earth (only depends on luminosity)
again, lowest magnitude highest brightness
36
Why do we see fewer stars in top left and bottom right of HR diagram?
Top left = large mass main sequence stars -> short lifetime -> evolved into red giants -> so few here at one time
Bottom right low mass stars , lower luminosity, very faint + less detected
37
How will the absolute magnitude of a star alter when it becomes a red giant?
decrease
- larger radius + larger sa so will transfer more energy
38
How can you deduce the relative ages of galaxies from HR diagrams?
HR diagram showing only ms stars indicates younger galaxy than one showing less main sequence stars, and more red giant etc stars
enough time has passed for a ms to turn into an rg or a wd
39
Describe the past evolution of the universe
Universe started 13.8 billion years ago with Big Bang
universe expanded from sate of high density + temp
as universe expanded universe cooled + decreased in density
as it cooled atoms, molecules, stars + galaxies formed
40
What is CMBR radiation and how does it support the Big Bang theory?
cosmic microwave background radiation emitted during Big Bang
emitted as gamma radiation
wavelength stretched because universe is expanding
microwave radiation present everywhere leftover from Big Bang, which implies all parts of the universe were in contact a long time ago
41
If a galaxy is moving towards us, how would you expect the frequency of light to change?
frequency will increase (blue shift)
42
If a a galaxy is moving away from us, how would you expect the frequency of light to change?
Frequency will decrease (red shift)
43
If a a galaxy is moving away from us, how would you expect the frequency of light to change?
Frequency will decrease (red shift)
44
How does red shift of galaxies support the Big Bang theory?
the further the galaxy is from earth, the greater the red shift
the greater the red shift, the faster the galaxy is moving away
speed of galaxies increases with increased distance
relationship between speed and distance implies expansion from a single point or since Big Bang
45
What is the Doppler effect?
when moving away from observer, apparent wavelength increases, decrease in frequency
when moving towards observer, wavelength decreases, frequency increases
wave speed is constant
46
Do furthest galaxies move away from us faster?
Yes, they have more red shift
47
The Doppler Effect
The change of wavelength (and frequency) of the waves from a moving source depending on whether they are in front of or behind the observer.
48
How does a sound change when the source is moving towards you?
> The sound waves get compressed.
The wavelengths get more frequent.
The pitch is higher.
49
How does a sound change when the source is moving away from you?
> The sound waves get spread out.
The wavelengths get less frequent.
The pitch is lower.
50
Red Shift
> When an object is moving away from us.
The wavelengths get more spread out.
This causes the spectrum of light to shift to the red side.
51
Blue Shift
> When an object is moving towards us.
The wavelengths get more squashed together.
This causes the spectrum of light to shift to the blue side.
52
The faster a star or galaxy is moving (relative to us) …
… The larger the red/blue shift.
53
Evidence for the expanding universe.
> The light from distant galaxies is red-shifted.
> The further the galaxy is from us, the bigger the red-shift is.
54
The Big Bang Theory
The theory that space, time and matter were all created in a massive explosion staring from a very small initial point and the universe has been expanding ever since.
55
The Steady State Theory
An outdated theory that proposed the galaxies were being pushed apart by ‘white holes’ that were leaking matter into the universe.
56
Cosmic Microwave Background Radiation
> Created as high energy gamma radiation after Big Bang.
Been travelling through space ever since.
As the universe expanded, its wavelengths stretched to longer wavelengths and now it it detected as microwave radiation.
57
Evidence for the Big Bang:
Cosmic Microwave Background Radiation- The BBT is the only way of explaining it.
58
Evidence for the Big Bang:
Cosmic Microwave Background Radiation- The BBT is the only way of explaining it.
59
The future of the universe if its density is less than a certain amount:
> The universe will expand forever.
The stars will die out.
The universe ill end in a Big Yawn.
60
The future of the universe if its density is more than a certain amount:
> The universe will stop expanding and do the reverse.
> The universe will end in a Big Crunch.
61
Sun:
a star, a large celestial object that undergoes fusion
62
planets:
objects that orbit the sun (must be spheres and have their own orbit)
63
moons:
natural objects that orbit a planet
64
satellites:
man made objects that orbit planets
65
Oort Cloud:
region of icy particles on the outside of the solar system
66
meteorodes:
smaller rocks in space
67
asteroid:
rock with a diameter larger than 10m
68
comets:
made of ice + dust that come from the edge of the edge of our solar system
69
What is an equation relating circumference, orbital speed and time?
orbital speed = circumference/time take for one orbit
70
How do you calculate energy output?
E = mc^2
71
How do you do red shift calculations?
observed wavelength / original wavelength = recessional velocity / speed of light (3x10^8)
72
what does steady state theory suggest?
that the universe has always existed
73
what does the red shift theory state?
that all galaxies are moving away from each other, implying that they are expanding. The further away the faster the galaxies are moving.
74
what is CMBR?
cosmic microwave background radiation. It is the radiation from the Big Bang that has been stretched.
75
How does a nebula become a protostar?
The gas and dust in a nebula is gravitationally attracted to each other. Therefore it condenses and when the gas and dust is packed at a high enough temperature and pressure, fusion begins.
76
What are the features of a main sequence star?
Fusion is stable and stars spend the most of their life cycle in this stage.
77
What happens to a large mass star after is has been a main sequence star?
super red giant -> supernova -> neutron star/black hole
78
What happens to a low mass star after it has been a main sequence star?
red giant -> white dwarf -> red/black dwarf
79
What colour is the ‘hottest’
white
80
what colour is the ‘coldest’
red
81
what is apparent magnitude:
the brightness of a star as we see it on earth
82
what is absolute magnitude:
the brightness of stars assuming that all stars are the same distance away from us (10pc)
83
what is the Doppler effect?
when the apparent wavelength and frequency changes due to the movement of a source towards or away from the observer.
84
if a star is moving towards you the colour will appear…
blue
85
if a star is moving away from you, the colour will appear
red
86
what is a sun?
a star, a large celestial object that undergoes fusion
87
what are planets?
objects that orbit the sun (must be spheres in their own orbit)
88
what is a moon?
natural objects that orbit planets
89
what is an asteroid?
rocks larger than 10m diameter
90
what is an Oort Cloud?
a region of icy particles on the outside of our solar system
91
What is a universe?
a collection of galaxies
92
what is a galaxy?
a collection of stars (Milky Way)
93
How does a nebula turn into a protostar?
the gas and dust in a nebula is gravitationally attracted to each other and therefore it condenses. when it is packed together at a high enough pressure and temperature, fusion begins.
94
What is the apparent magnitude?
a measurement of the brightness of a star as we see it
95
What is absolute magnitude?
a measurement of the brightness of a star assuming that all stars are the same distance away from us (10Pc)
96
What is CMBR?
Cosmic microwave background radiation is radiation from the Big Bang that has been stretched and is now present on earth.
97
How does the red shift of galaxies prove the Big Bang?
all galaxies are moving away from each other which implies that they are expanding. the further away, the faster the galaxies are moving. all galaxies have been moving away from us for the same amount of time so they must have started in the same place
98
What celestial body do comets orbit?
The Sun
99
How do planets orbit the Sun?
In nearly circular orbits
100
Describe the orbit of a comet
Comets have very elliptical, elongated orbits. They travel much faster when moving near to the Sun, because the gravitational force is much stronger (the force is inversely proportional to the square of the distance from the centre of gravity)
101
orbital speed =
o.s. = 2π r/T
102
What is the universe?
Collection of billions of galaxies
103
What is the Milky Way galaxy?
Our galaxy; a collection of billions of stars
104
What is the solar system?
Collection of all the celestial bodies (planets, natural satellites, comets, asteroids etc.) which orbit the Sun
105
What happens to the orbital speed of an child on a roundabout in a park if the child halves their distance to the centre of the roundabout?
v = 2πr / T
If radius is halved, orbital velocity is halved for the same time period.
106
What is a galaxy?
A large collection of stars- made of billions of stars rotating about a central point
107
What type of orbit does a comet have?
Very ellipitcal- with the Sun or star at one focal point.
108
What is the equation which links orbital speed, radius of orbit and time period?
orbital speed = 2π x radius / time period
v = 2π r / T
109
What is the unit for time period (T)?
seconds (s)
110
What is the unit for orbital speed?
metres per second
or kilometers per hour
111
What happens to the movement of a comet during one complete orbit?
A comet accelerates towards the star. The comet is travelling at its highest velocity as it whips round the star. As it moves away from the star it decelerates. At the furthest distance from the star the comet will be travelling at its slowest velocity.
112
What type of orbit does a satellite have?
Circular orbit around the Earth
113
In which position will the comet be travelling the slowest and why?
The comet travels the slowest at A because the gravitational pull is the smallest at A.
Gravitational pull decreases as distance between celestial objects increases.
114
In which position will the comet be travelling the fastest and why?
The comet travels the fastest at C because the gravitational pull is the largest at C.
Gravitational pull increases as distance between celestial objects decreases.
115
What happens to the orbital speed of an child on a roundabout in a park if the child halves the time period of the roundabout?
v = 2π r / T
If time period is halved, orbital velocity is doubled for the same radius.
116
What is the name of our galaxy?
The Milky Way
117
What is the universe?
A large collection of billions of galaxies
118
In which position will the comet be travelling the slowest and why?
119
How many galaxies are found in the universe?
billions of galaxies
120
What is a geostationary orbit?
When a satellite is placed in high orbit above the equator with a speed such that its time period (T) is equal to 24 hours.
This means the satellite is always over the same point of the Earth- it can be used for satellite television.
121
Name one natural satellite orbiting the Earth
The Moon
122
In the image of a planet orbiting the Sun, how would you label the gravitational pull acting on the planet?
An arrow downward pointing towards the Sun
123
Which type of orbit does a planet have?
circular, slightly ellipitcal or very elliptical
Nearly circular, slightly elliptical
124
What happens to the orbital speed of an child on a roundabout in a park if the child doubles the time period of the roundabout?
v = 2π r / T
If time period is doubled, orbital velocity is halved for the same radius.
125
How could you calculate the orbital speed of a person standing on the very edge of a roundabout?
Use a stopwatch to time 5 full rotations and divide this time by 5. This is the time for one revolution or the time period (T)
Measure the radius (r) of the roundabout with a tape measure.
Calculate orbital speed = 2πr/T
126
Which side of the orbital path is the comet accelerating? decelerating?
The comet accelerates from A to D to C since the gravitational pull is in the same direction as its movement. The gravitational pull is speeding it up.
The comet decelerates from C to B to A since the gravitational pull is in the opposite direction to its movement. The gravitational pull is slowing it down.
127
In which position will the comet be travelling the fastest and why?
The comet travels the fastest at C because the gravitational pull is the largest at C.
Gravitational pull increases as distance between celestial objects decreases.
128
Which orbital path shows the orbit of a comet?
Blue or red?
Blue orbital path
Comets have elliptial orbits with time period of many years
129
What force keeps the stars together in a galaxy?
Gravitational pull
130
Approximately how many stars are found in a galaxy?
billions of stars
131
Galaxies rotate
If one side of the galaxy is moving toward us and one side is moving away from us, what would we observe in terms of the light we receive from each side of the galaxy?
Side moving towards us will be blueshifted, the light will have a smaller wavelength and higher frequency- shifted towards the blue end of the spectrum
Side moving away from us will be redshifted, the light will have a large wavelength and lower frequency- shifted towards the red end of the spectrum
