Further physics - studying the universe Flashcards
1
Q
How does the sun appear to move across the sky?
A
From east to west (I remember it by alphabetical order)
2
Q
What is the time between the sun appearing at its highest point one day and the next called?
A
The solar day
3
Q
How long is the solar day?
A
24hours
4
Q
How long does it take for the moon to appear in the same place in the night sky from one day to the next?
A
24 hours + about 50 minutes, which is the time that the earth takes to rotate further to catch up with the moon as it orbits us.
5
Q
How long does it take the stars to appear in the same place?
A
Slightly less than 24 hours.
6
Q
What is a sidereal day?
A
The time taken for the earth to rotate 360 degrees
7
Q
How long is the sidereal day?
A
23 hours 56 minutes
8
Q
Why is the sidereal day shorter than the solar day?
A
We are orbiting the sun, so we need an extra 4 minutes to allow for the movement of the earth through space to put the sun where it was the previous day.
9
Q
What does the moon orbit?
A
The earth
10
Q
What causes the moon to be visible from earth?
A
It reflects some of the light from the sun.
11
Q
How much of the moon is lit by the sun at any time?
A
Half.
12
Q
Why does the moon appear to change shape from earth?
A
It is due to the change in the amount of the lit side of the moon that we can see.
13
Q
What is the changing shape of the moon called?
A
The phases of the moon.
14
Q
When the moon is almost directly between the earth and the sun, what shape moon do we see?
A
The crescent of the new moon
15
Q
When the earth is almost directly between the sun and the moon what shape moon do we see?
A
The round full moon.
16
Q
What is the time between one full moon and the next?
A
29.5 days.
17
Q
What is the time between one full moon and the next called?
A
A lunar month.
18
Q
What happens when the sun, moon and earth are directly in line?
A
It creates an eclipse
19
Q
How does a solar eclipse happen?
A
The moon comes between the sun and earth, and the moons shadow falls on earth.
20
Q
How can the tiny moon blot out the whole sun?
A
It is much closer to the earth, and they apparent size of the two objects from earth is almost the same.
21
Q
Why can a solar eclipse only be seen from part of the earth?
A
The moon is a lot smaller than the earth, so the moons shadow covers a relatively small area.
22
Q
How can a lunar eclipse happen?
A
When the moon passes into the earth’s shadow.
23
Q
From where on earth is a lunar eclipse visible?
A
From any part where the moon is visible at that time.
24
Q
Why don’t eclipses happen every time the moon orbits the earth?
A
The moon does not orbit the earth at the same angle as the orbit of the earth around the sun, the earth moon system is tilted slightly.
25
Which planets can be seen from earth with the naked eye?
Mercury, Venus, Mars. Jupiter and Saturn can also be seen, despite the distance, as they are very large objects.
26
What does the word planet actually mean?
It comes from the Greek for "wandering star", as the planets move across the other stars.
27
As the planets orbit the sun, and we keep orbiting too, what happens to the distance between us and the planets?
It changes.
28
What happens to the apparent brightness of the planets as the distance between us changes?
It changes.
29
What happens to the stars as the earth rotates?
They, and the planets, appear to move east-west.
30
What happens to the position of the planets against the background of the stars?
It changes due to their orbits around the sun.
31
Sometimes the planets actually go backwards. What is this called?
Retrograde motion.
32
What happens to the speed of an object if the orbit is smaller?
It speeds up. (Think of a somersault, tight tuck = quicker movement)
33
What is the implication of the different speeds of the planets, as seen from earth?
Sometimes they will be moving towards us, at other times they will be moving away from us.
34
If Mars is on the opposite side of the sun from us, what will it's speed seem to be, from earth?
Very fast, as we are moving in the opposite direction = we seem to see the sum of our speed, and the speed of Mars.
35
If we are on the same side of the sun, what speed is Mars doing (seen from Earth)
We would see the speed of Mars as the difference of the two speeds of Earth and Mars - but we are going more quickly, we are closer to the Sun, so it actually appears to go backwards for a bit.
36
What really happens to the speed of Mars as it orbits the sun?
It stays almost constant (remember that the orbits are not completely round, so the speed has to vary a little)
37
Where is the Pole star, relative to Earth?
Above the North Pole.
38
What is the Pole Star really called?
Polaris.
39
Why do the stars visible from earth change over the year?
We only see the stars at night, from the half that faces away from the sun, so we are facing a different part of the night sky as we orbit the earth. Polaris remains visible from the whole of the northern hemisphere of earth.
40
How would you describe the position of a star?
The angle of declination (distance above the equator) and the angle of right ascension (distance east-west).
41
What is the celestial sphere?
An imaginary globe around the earth that has the light of every celestial object projected on to it.
42
What is the angle of declination measured in?
Degrees, minutes, seconds.
43
What is the angle of right ascension measured in?
hours, minutes, seconds. 1 hour = 15 degrees.
44
When is the angle of right Ascension measured?
At the point where the sun crosses into the northern hemisphere, this happens at the spring equinox.
45
What is the spring equinox?
The day in spring when day and night are exactly the same length.
46
How does light travel?
As a wave.
47
How is light affected by the medium it is travelling through?
The speed varies.
48
What is the speed of light in a vacuum?
300,000,000 m/s = 3 x 10^8 m/s
49
If the speed of the light changes in different mediums, what happens to the frequency and the wavelength?
The frequency stays the same, so the wavelength has to be shorter if the speed is reduced.
50
When waves hit a boundary between two different mediums, where they will travel at different speeds, what will happen?
The light is refracted (bent).
51
Why is light refracted?
Think of a car going from the road to say, deep pebbles at an angle, the wheel that hits the pebbles first will slow down and cause the whole car to swing round it, changing direction.
52
How do we use refraction?
It is how a lens focuses light.
53
Draw the refraction diagram for a convex lens.
Make sure you use a ruler, and have sudden changes of direction at the edges of the lens, marks will not be awarded for bendy light waves!
54
What do convex lenses do to light?
Bring it together.
55
The power of a lens in measured in?
Dioptres
56
What is the formula for the power of a convex lens?
Power (dioptres) = 1/focal length
57
What is the focal length?
The distance from the lens that all the light will meet.
58
Light entering the eye from the objects around us is not parallel. Why do we say that the light from stars is?
The distances are so large that the light rays are effectively parallel.
59
If an object is on the principal axis of a lens, where will the image be?
At the focal point.
60
If an object is off the principal axis of a lens, what will happen to the image?
It will still be focused, but at one side of the focal point (opposite to the real object).
61
What are astronomical objects that are bigger than a point of light called?
Extended objects.
62
Name some extended objects?
Sun, moon, galaxies, planets and their moons
63
You will need to be able to draw ray diagrams - page 44 of the revision guide.
Ruler!!!
64
What does a simple refracting telescope contain?
Two convex lenses, the objective lens and the eyepiece lens.
65
What does the objective lens in a refracting telescope do?
It is a low power lens, with a long focal length. It has a large diameter to collect the most possible light.
66
What does the eyepiece lens in a refracting telescope do?
It is a small lens, higher power, short focal length. It acts as a magnifying glass to the image formed by the objective lens.
67
What is the function of the telescope?
To make objects appear larger.
68
How does the telescope make the image larger?
It increases the angle between the image and the axis of the telescope - so it is spreading the image out.
69
How do you measure magnification of a refracting telescope using the angles from the axis?
The angle from the axis of light leaving the telescope/ the angle from the axis of the light entering the telescope.
70
What does the magnification of a telescope actually depend on?
The ratio of the power of the lenses, and therefore the ratio of the focal lengths.
71
How would you measure magnification of a refracting telescope?
Magnification = focal length of objective lens / focal length of eyepiece length.
72
What is the magnification of a telescope always greater than?
1 - otherwise it is not helping
73
How does focal length relate to power?
f = 1 / power
74
Work out the magnification of a telescope where the eyepiece has a power of 100, and the objective has a power of 20.
```
f = 1 / power. fe = 1/ 100 = .01 fo = 1/20 = .05
magnification = focal length of obj. lens/ eye.lens
magnification = 0.05 /0.01 = 5
```
75
How does a concave mirror reflect light?
As the mirror is curved, and the angle of reflection must equal the angle of incidence, it brings the rays together at a focal point.
76
How can a concave mirror be used in a telescope?
It is used instead of the objective lens, then a second mirror is used to reflect the captured image into the eyepiece
77
Why us a concave mirror in a telescope rather than a convex lens?
A mirror is lighter (as thinner), easier to support (as can be supported all the way behind, not just at the edges like a lens) so can be made much larger, easier to manufacture, no chromatic aberration.
78
What is chromatic aberration?
When light passes through a lens different colours (wavelengths) of light are diffracted by different amounts (like a prism) so you get colours on a telescope image where there should not be any (eg the moon has a coloured edge)
79
Who first built a telescope using a mirror?
Newton, in 1668. Mr Apple himself :)
80
What sort of lens is the objective lens of the telescope?
Convex
81
What sort of mirror in a telescope?
Concave.
82
What is diffraction?
The waves spread out after going through a small gap
83
What does the amount of diffraction depend on?
The wavelength of the wave, and the size of the gap in comparison to the wavelength.
84
What does the long wavelength of radio waves mean for the diffraction of radio waves?
They can be diffracted considerably, so,for instance, you can receive radio waves in a valley because the hills have diffracted the waves, even if you don't have a direct line of sight to the transmitter.
85
What sort of telescope is Jodrell Bank?
Radio
86
What other sorts of telescopes are there?
eg X-ray, infrared, microwaves
87
What is the aperture of a telescope?
The size of the objective lens/mirror
88
What happens when the waves entering the telescope are diffracted by the small aperture?
You get blurry images.
89
What must you do to produce clear images?
Increase the size of the aperture to be longer than the wavelength.
90
What type of telescope will be most affected by diffraction?
Radio telescopes, as the wavelength of radio waves is so large.
91
What do we do to reduce diffraction in radio telescopes?
Join multiple dishes together in an array to create a telescope with an aperture hundreds of metres across.
92
What does a star's spectrum show?
How much energy of each wavelength it emits.
93
What can studying the spectrum of a star tell us?
Information about composition and temperature.
94
When can you see the spectrum of visible light from the sun?
In a rainbow.
95
What could you use to create a spectrum?
A prism.
96
How does a prism split light?
The light is refracted as it enters the prism, different wavelengths are refracted by different amounts.
97
What are the colours of sunlight?
Red, Orange, Yellow, Green, Blue, Indigo, Violet (Richard Of York Gave Battle In Vain)
98
If the wavelength is shorter, what happens to the amount of refraction?
It increases
99
What colour light is refracted the most?
Violet.
100
What else can produce a spectrum?
A diffraction grating
101
What is a diffraction grating?
A series of very finely spaced gaps that light shines through; or a series of finely drawn lines on a surface that light reflects off (eg a cd!)
102
How many lines per cm on a diffraction grating?
Thousands.
103
As different colours are diffracted by different amounts, what would you see if you look at a diffraction grating, then move your head?
The colours will change
104
What did astronomers notice about quasars when they were first discovered?
The spectrum showed a very large redshift.
105
What does a large redshift mean?
The object must be moving away from us very quickly
106
Where would an object that is moving away so quickly be?
A long way away from us (expanding universe)
107
Why did some astronomers not believe that quasars were as far away as the red shift suggested?
Something that far away would not be visible.
108
Why are quasars only seen far away?
There are no quasars in the recent universe, they seem to have happened only at the beginning.
109
What are quasars?
No one really knows. They seem to be tied up with galaxy formation in the early universe, they only last a short time (maybe a billion years or so), none are being formed now, and they (probably) leave behind a black hole.
110
What is parallax?
The way an object seems to "jump" against the background if we look at it from slightly different viewpoints. Nearby objects move more.
111
What happens to the closer stars compared to the more distant stars as we move around the sun?
They move slightly.
112
How would you find the parallax angle of a nearby star?
You take two measurements of the close star against the background of distant stars, 6 months apart, to get the parallax angle, which is half the angle that it has appeared to have moved in the six months. By geometry, the parallax angle p is half of the difference of the 2 measurements.
113
How are parallax angles measured?
In seconds of an arc (arcseconds). One second = 1/60 minute. I minute = 1/60 of a degree.
114
What is the parsec?
A unit of length that is equal to 3.26 light years.
115
What defines a parsec?
Distance (parsecs) = 1 / parallax angle (seconds)
116
What are parallax angles like?
Extremely small - our closest star, Alpha Centauri, has a parallax angle of 0.75 degrees, so it is 1.3 pc (parsec) from earth. Don't bother getting your protractor out for this job ;)
117
What is 1 arcsecond like?
The angle you would have to move your eyes to look from one side of a penny to the other - if the penny were 1.5 km away.
118
What is the angular diameter of the full moon, roughly?
1800 seconds. ( Don't bother learning, just for comparison)
119
What is the definition of a light year?
The distance travelled by light in one year.
120
How far to Alpha Centauri, our nearest neighbour?
Just over 4 light years.
121
How far to our nearest galaxy?
Over 2 million light years. (It is Andromeda, by the way, part of the "close cluster".)
122
What is the total energy output of a star?
Luminosity
123
How would you define luminosity?
The total energy output of a star, across all wavelengths, in all directions, in one second
124
What does the luminosity of a star depend on?
Size (larger surface area to emit radiation from); temperature (the hotter the star, the more radiation).
125
How does the temperature of the star affect the colour?
hotter stars are bluer, cooler stars are redder.
126
What is a star's apparent brightness?
the mount of energy that reaches the earth, ie how bright it is.
127
What does apparent brightness depend on?
The luminosity of the star; how far away the star is (as the radiation spreads out over a much wider area).
128
How does apparent brightness vary?
The inverse square law - going twice as far away means the radiation has to cover four times the area.
129
If there are two stars of equal luminosity, but one is 10 times as far away, what will be the apparent brightness of the further star?
1/100 of the nearer star.
130
What do you call a star that shows regular variation in brightness?
A Cepheid variable.
131
What do you call the period of dimming, and going back to the maximum, of a Cepheid variable?
The period.
132
What is the relationship between the period of a Cepheid variable, and the luminosity?
There is direct correlation.
133
How can a Cepheid variable be used to calculate the distance?
The apparent brightness can be used as the luminosity can be calculated from the period .
134
What makes a Cepheid variable behave in such a loony way?
They are stars that vary between a larger, brighter state and a smaller, denser one. They are very luminous variable stars, of a class that was especially massive and hot, using up their fuel early, leaving them in this pulsating condition.
135
What did the use of telescopes reveal about the Milky Way?
That it consists of millions of stars
136
What did people realise about the Milky Way when it was found to be millions of stars?
That it is a galaxy, and that we are part of it.
137
What allowed an estimate of the size of the Milky Way?
The use of Cepheid variables
138
What did Harlow Shapely do?
He used Cepheid variable stars in groups of stars called globular clusters to find the luminosity, and therefore to get an estimate of the size of the Milky Way.
139
What size did Shapely estimate the Milky Way at?
300,000 light years.
140
What incorrect conclusion did Shapely come to as a result of his estimate of the size of the Milky Way?
He thought that the Milky Way was the only thing in the universe
141
What else, apart from the Milky Way, was found using telescopes?
Fuzzy bright clouds of light, called nebulae.
142
What were the two schools of thought about spiral nebulae?
Some people thought that they were nearby clouds of dust, possibly areas of planetary formation; others thought that they were galaxies so far away that they appeared fuzzy (the Island Universe Hypothesis)
143
When was the Curtis-Shapely debate held?
1920
144
What did Curtis believe?
The Island Universe Hypothesis; the Milky Way is 30,000 ly across.
145
What did Shapely believe?
Our galaxy is about 300,000 ly (light years), the only object in the universe; spiral nebulae are nearby, just small clouds of gas,
146
Who found evidence to resolve the debate, 5 years later?
Edwin Hubble (the Hubble telescope is named after him)
147
What did Hubble find?
Evidence that the spiral nebulae were other galaxies.
148
Who was right, Curtis or Shapely?
Neither, Curtis was right about the Island Universe but wrong about the size of the Milky Way; Shapeley was closer about the size of the Milky Way but wrong about the size of the universe.
149
When did Edwin Hubble show that some nebulae were actually galaxies?
1925
150
What made him think that some nebulae were galaxies?
He discovered a Cepheid variable in the Andromeda nebula which had a period of 31 days which meant that it should have been very bright, but it was very faint. He calculated that it must be at least 1 million light years away, so outside of our own galaxy.
151
How large is the known universe?
Around 14 billion light years across.
152
When you compare the spectrum of light from another galaxy to the spectrum from ours, what do we see?
The spectrum is shifted to the red end.
153
What does red shift mean?
The galaxy is moving away from us.
154
What have we found about the motion of galaxies?
Most are moving away from us
155
Why are some galaxies moving towards us if the universe is expanding?
We are gravitationally bound to the "close cluster" of galaxies, so we are moving towards Andromeda.
156
What did Hubble find about the speed of recession versus the distance?
They are directly proportional.
157
What is the equation for the speed of recession?
Speed of recession (km/s) = Hubble constant (s^-1) x distance (km) or Speed of recession (km/s) = Hubble constant((km/s)/Mpc) x distance (Mpc)
158
How did Hubble's discovery of receding galaxies support the big bang theory?
The way that everything is moving apart supports the theory that space itself is expanding.
159
What is the Big Bang Theory?
The universe appeared at a single point about 14 thousand million years ago.
160
What do all objects emit?
Electromagnetic radiation. (Except dark matter. If it exists).
161
What increases the amount of radiation an object emits?
Heat
162
What happens to the wavelength of radiation an object emits as it gets hotter?
The frequency goes up, so the wavelength gets shorter
163
What does the colour and luminosity of a star depend on?
Surface temperature.
164
Where is the star hottest, and densest?
In the middle. The sun has 16 million C there.
165
Where does most of the nuclear fusion in a star happen?
In the centre.
166
What do the nuclear reactions in the centre of the star release?
Photons.
167
What happens to the photons?
They transfer radiation in the radiation zone of the star.
168
How is heat distributed closer to the surface of the star?
Convection currents.
169
Where is the layer of the star that radiates the energy into space?
The photosphere, the outer layer of the star.
170
What is the rainbow?
A continuous spectrum that covers all the wavelengths of visible light.
171
What is a line spectrum?
When there are just a few coloured lines at specific wavelengths.
172
What sort of line spectra do different elements produce?
Different ones.
173
Hot gases give off light radiation. If you split this light, what do you get?
A line spectrum specific to the gas being heated.
174
If white light is shone through a gas the spectrum produced will have....
black lines where some of the light is absorbed.
175
What is another name for a line spectrum?
An emission spectrum.
176
What do you call the spectrum that is left after the gas has taken some of the light?
An absorption spectrum.
177
Stars are very hot objects so they emit?
A near continuous spectrum of radiation.
178
What can you see if you look closely at the emission spectrum of a star?
Hundreds of dark lines.
179
What are the lines on the spectrum of a star caused by?
The gases in the "cool" outer parts of the star absorbing certain wavelengths of light, different elements absorb different wavelengths and produce different spectra.
180
What can you learn by studying the lines on the spectrum of a star?
The chemical composition of the star.
181
What happens when an atom absorbs a photon?
It may knock an electron off.
182
What is it called when you remove an electron from an atom?
Ionisation.
183
What do different elements require to ionise?
Different amounts of energy.
184
Is the spectrum of an ion the same as the atom?
No.
185
What can you determine by looking at the ions that are present on a star?
You can determine how energetic the absorbed ions are, and therefore how hot the star is.
186
What makes an atom emit light?
An electron losing energy.
187
What do the line spectra indicate?
Electrons don't have a continuous range of energy, if they did the light spectrum would be continuous.
188
Electrons in an atom have what sort of energy levels?
Specific energy levels.
189
What is emitted when an electron drops from one energy level to another?
A photon.
190
What do different elements have in relation to the energy levels of their electrons?
Different elements have their own set of specific energy levels, so different elements have different emission spectra.
191
How does the idea of electron energy levels explain absorption spectra?
Each element's electrons need a specific amount of energy to "jump" to a higher level.
192
What is the difference between temperature and thermal energy?
Temperature does not take into account how much of something there is, so a hot bath will have more thermal energy than a burning candle.
193
What is temperature a measure of?
How concentrated the thermal energy is.
194
What does the temperature of a substance measure?
The average kinetic energy of the molecules.
195
What is the temperature when all the molecules have no kinetic energy?
Absolute zero.
196
What happens as you increase the temperature of a gas?
The molecules move faster, which causes more collisions with the walls of the container, and more energy in the collisions, so the pressure goes up. If you keep the pressure constant (eg by having the gas in a balloon) then the volume will increase.
197
What happens if you cool a gas?
The molecules move slower, which causes fewer collisions with the walls of the container, and less energy in the collisions, so the pressure goes down. If you keep the pressure constant (eg by having the gas in a balloon) then the volume will decrease.
198
If you plot a graph of volume of a gas v temperature,you get a straight line. What temperature would give a volume of zero?
-273C
199
Why is -273C the coldest possible temperature?
The molecules have no kinetic energy at this point.
200
What is -273C in Kelvin?
0K
201
What would you get if you plotted a graph of pressure of a gas versus temperature?
You would get a straight line, with a pressure of 0 at -273C
202
What is Boyle's law?
Pressure x volume = constant.
203
What are the three gas laws?
Pressure x volume = constant; pressure/temperature = constant; volume/temperature = constant.
204
How can the three gas laws be combined?
pressure x volume / temperature = constant.
205
What are nebulae (modern, not 1920s)
Immense clouds of molecular gas.
206
What do the nebulae contain, mainly?
hydrogen, helium, and dust
207
What slowly pulls the dust and gases together?
Gravity
208
Why do nebulae form unstable regions?
The greater density of some regions means that they are more likely to collapse to form even denser regions.
209
How long do the denser regions remain stable?
While the outward pressure balances the gravitational force.
210
What happens as a nebula's dense area gets more dense?
The volume of the gas decreases, the gas particles move faster so the temperature increases, and the pressure and gravitational force are balanced again.
211
What happens when the temperature has risen so much that the area of the gas cloud glows red?
It is known as a protostar, and it keeps on attracting material to itself.
212
What happens as the protostar spends a few million years attracting more material to itself?
As it gets more material it exerts a stronger force of gravity, so it attracts more material, which increases the gravity....
213
What eventually happens to the protostar?
It gets so hot and dense in the centre that nuclear fusion can start and it becomes a star.
214
What is a brown dwarf?
A protostar that did not reach ignition, and cooled.
215
How much energy is produced by the nuclear fusion in the sun?
3 x 10^26 Joules per second.
216
What is the material at the centre of the sun like?
It is at over 15 millions Kelvins, denser than anything on earth, but still a gas due to the heat.
217
What happens to atoms at very hot temperatures?
They become a plasma of ions and electrons all moving at incredibly high speeds. (Note - 21st century describe a plasma as a gas!)
218
Given that most of the sun is hydrogen, what does that make most of the ions?
A single proton.
219
Fusion is not easy, how long may a proton have to wait before it gets fused?
A billion years.
220
What is the high output of energy from the sun due to, if fusion is so difficult?
The mass of the sun.
221
What is the series of reactions to make helium from the 4 protons called?
p-p cycle.
222
What happens first in the p-p cycle?
2 protons fuse (after about 10^9 years) to form a deuterium (heavy hydrogen) nucleus, one proton, one neutron - this gives off a positron and a neutrino.
223
What happens as the second stage of the p-p cycle?
The deuterium fuses with a hydrogen nucleus to form helium 3 (takes about 1 second for this stage) and a gamma ray is given off.
224
What happens at the third stage of the p-p cycle?
Two Helium 3 nuclei fuse (after 10^6 years) to form proper helium 4, and this reaction also gives off two protons (hydrogen nuclei) which have to wait another billion years or so to be fused again.
225
What happens to the mass of the reactants in the p-p cycle?
The mass numbers are conserved, but the mass of helium-4 is slightly less than the mass of 4 hydrogens. This loss of mass is what powers the sun.
226
What is Einstein's equation?
E = mc^2
227
How much mass does the sun lose per second?
3 x 10^9 kg every second.
228
What sort of star is our sun?
A main sequence star.
229
What is happening during the main sequence?
Hydrogen is being fused into helium in the core, and the outward pressure of the gas and radiation is balanced by the gravity.
230
What is needed to form the heavier elements?
Pressures and temperatures much higher than our sun, so bigger stars.
231
What does fusing lighter elements to create the elements up to iron release?
Energy.
232
How do we get the elements heavier than iron?
They are only formed in the final stages of the life of the largest stars.
233
What happens when the code of a star stops releasing energy?
Gravity will begin to crush the star.
234
What is a Hertzsprung-Russel diagram?
A plot of luminosity of a star (y) against the temperature (x).
235
What does a Hertzsprung-Russel diagram show?
Three main groups of stars - main sequence, giants and supergiants, and white dwarfs.
236
What is a white dwarf?
A star that is no longer fusing anything, and is just cooling slowly.
237
What happens as a star runs out of hydrogen?
Fusion is reduced, less energy is produced and the pressure drops.
238
What happens to the size of a star if the internal pressure drops?
The star will shrink down as gravity now exceeds the internal pressure.
239
What happens as the star collapses because fusion has slowed down
As the star collapses the density and temperature increase and fusion can restart, this increases the pressure and the star expands enormously.
240
What happens to the temperature of the star as it expands?
The photosphere cools and the star becomes a red giant or supergiant.
241
What happens to the last of the hydrogen in the centre of a star at least eight times the mass of the sun?
It fuses to form helium, which fuses to form beryllium and carbon, and then heavier element up until iron.
242
What will happen to the sun when it has used all the hydrogen in the core?
The core collapses, but the outer layers are blown off into space. The remnant is a white dwarf and a planetary nebula, cooling to a black dwarf.
243
What happens when a star has mainly iron left in the core?
Further fusion would absorb energy rather than releasing it, so the star cannot generate energy and undergoes a catastrophic collapse, a supernova. The heaviest elements are formed during this collapse, and the star's explosion scatters mass into space.
244
What is left after a supernova?
A neutron star - the star is so dense that there are only neutrons, no protons and electrons.
245
What happens if the star was so massive that it can keep collapsing beyond the neutron star stage?
A black hole.
246
Why is finding planets circling other stars difficult?
They are too small to see; they don't give out their own light; light reflected from them is lost in the glare from the star,
247
How do astronomers find planets circling other stars?
The wobble method, or the transit method.
248
What is the wobble method of finding a star?
The star will be orbiting the centre of gravity of the star/planetary system, if there is a massive planet it can produce a "wobble" in the star, which can either be seen, or detected in the light emitted from it by changes to the spectrum (shift due to Doppler effect).
249
What is the transit method of finding a planet?
The planet passing in front of the star will absorb some of the light given out by the star, so the apparent brightness of the star will change in a regular manner as the planet orbits.
250
How many planets have been detected?
Hundreds.
251
What are most of the planets that we have found like?
Huge (like Jupiter) and close to the sun, because they are the easiest to detect.
252
What is the Goldilocks zone?
The area round the star that is thought to be habitable, where a planet could have liquid water.
253
Why do we think we might find life in water on other planets?
Life began on earth shortly after there was liquid water.
254
Why do many people believe that there must be life on other planets?
There are so many, so even if it is a rare event....
255
Has anyone found evidence that has been generally accepted for life on other planets?
No
256
Where are we looking for life in the solar system?
Mars; Gas giant moons eg Europa, one of Jupiter's moons.
257
Why would there be life on Mars?
It had liquid water once, so there may have been life which may be clinging on even now.
258
Why would there be life on Europa (and other moons)
Some have oceans of liquid water under a solid crust of ice, the water is warmed by tidal heating and there may be life that is relying on chemical energy.
259
What is SETI?
The search for extra-terrestrial life, a project that is listening for radio signals from space.
260
What are the advantages of a space telescope?
No atmosphere to absorb/refract radiation; no light pollution; no weather; can use parts of the electromagnetic spectrum that are absorbed by the atmosphere.
261
What are the disadvantages of a space telescope?
They are expensive to set up and maintain and repair; space programmes are very expensive and may not carry on, so repairs could become impossible.
262
How were the locations of the main ground based optical and infrared telescopes chosen?
High above sea level so above clouds, less atmosphere above them; cloudless nights; dry air and little pollution as particles in the air would scatter the light.
263
What are the problems of choosing remote sites for telescopes?
Transport can take a long time, roads need to be built; expensive to build due to extra transport required; most astronomers are too far away to use the telescope.
264
How have computers improved access to telescopes for astronomers?
Astronomers can control the telescope from anywhere in the world, and get the results; the telescope can be programmed to track an object, or to scan a specific area of space; the telescope can be positioned much more accurately than any human could do it; images can be processed by computer allowing processing of wavelengths that we cannot detect by the human eye.
265
What do you need to consider before building a new telescope?
Environmental and social impact near the telescope; working conditions for employees; cost.
266
Why do countries cooperate when building telescopes?
They are very expensive.
267
What is the proposed ELT?
Extremely Large Telescope, much too expensive for any one country
268
What is a gamma ray burst?
A sudden burst of very energetic gamma rays from space, but we don't know what causes them.
269
When do gamma ray bursts happen, and how long do they last?
Randomly, and they last from a few seconds to several minutes
270
How is international cooperation helping gamma ray burst research?
The SWIFT satellite detects a gamma ray burst, then sends the coordinates to observatories around the world, some of whom might be looking the right way.
271
When was the last supernova in our galaxy?
400 years ago.
272
What will be the first warning of a supernova?
A flood of neutrinos will be detected, but we won't know where they are coming from.
273
What will happen when the neutrinos are detected which are thought to give warning of a supernova?
Everyone (astronomers) will start looking, and when they find the supernova the information will be shared so that we can get as much information as possible.
274
How does the internet help astronomers?
There are too many images to be analysed by astronomers, the images are put on line with some simple software and anyone can help map our galaxy. People are still better than computers for that job.
