Term
| What are considered the atoms of the universe? |
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Definition
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Term
| What two questions are prompted when we learn that the universe is expanding? |
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Definition
What was it at the time of origin?
What fate does the future hold |
|
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Term
| How do we find the sun's size? |
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Definition
| Measure its angular size (how big it looks) and determine its distance (by using radar) |
|
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Term
What is the size of the sun (diameter)?
Compared to the earth? |
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Definition
It is 100 times the diameter of the Earth
1.4 million km in diameter |
|
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Term
| how many earths could fit in the sun? |
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Definition
|
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Term
| How we know the surface temperature of the sun? |
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Definition
| The colour of the light emitted by the sun tells us surface T |
|
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Term
| What is the sun's surface t? |
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Definition
|
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Term
| Is our sun really hot or cool or average for stars? |
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Definition
| It's relatively average, and we know because it's spectrum wavelength is not the hottest nor the coolest. Our sun is white mostly, but a blue star is far hotter |
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Term
| How do we find out what the outer surface of the sun is made of? |
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Definition
| By examining it's solar spectrum (tells us its 2/3 H, 1/3 He) |
|
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Term
| how we do know the interior composition of the sun? |
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Definition
| It's not easy! We have to first consider other things (like mass) before we can make assumptions |
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Term
| How do we find the mass of the sun? |
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Definition
| by examining how the earth moves in response to the sun's gravity. We ask how massive must the sun be for its gravity to make the earth rtoate at 30km/sec) |
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Term
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Definition
| 300,000 times the mass of the earth |
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Term
| Because the sun is 1m as big as the eart, but only 300,000 as massive, what do we know? |
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Definition
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Term
| What does the sun's density tells us about its composition? |
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Definition
| That is can't be made of the same material (rock) as the earth |
|
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Term
| how much light does the sun give off? |
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Definition
| About 1 kW per square metre |
|
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Term
| What did galileo understand through the behavior of sunspots? (2) |
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Definition
that the sun must rotate (because they move)
and that the outer parts of the sun must be fluid (not solid) |
|
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Term
| How do we know the sun's composition hasn't change much in a long time? |
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Definition
| Because there have been oceans of liquid water for at least 3 billion years |
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Term
| Compared to humans, does the sun produce a lot of energy? |
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Definition
| It contains a lot of energy, but only a tiny fraction of it "dribbles" out from the interior. Gram for gram, humans produce far more energy (more than 1000x more) |
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Term
| Why do we think the sun should be contracting? |
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Definition
| Because the sun's self gravity (the inward pull on all its atoms as they mutually attract each other) makes the sun want to contract to something smaller |
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Term
| And if we know the sun isn't shrinking, what is opposing it's self gravity? |
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Definition
We know now its the huge T! Lots of temperature means particles are moving fast, creating pressure and pushing up.
IT could have also been a rigid internal structure, like dart |
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Term
| Why could the sun not have a rigid structure? |
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Definition
| The gravitation of the sun is so strong it overwhelms all molecular and cystalline bonds |
|
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Term
| What is the interplay between the sun's heat and gravity? |
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Definition
| Stars must be really hot to resist the pull of gravity, but it is the inward pull of gravity that makes them hot in the first place |
|
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Term
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Definition
| Because huge clouds of interstellar gas start to contract under the influence of gravity. As they fall inward and collect together, the atoms collide vigorously. They wind up jiggling about furiously - in other words the material has become hot. |
|
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Term
| Describe the conversion of graivty to heat? |
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Definition
| Something has energy, gravity forces it to lose it's PE. So that energy is converted into KE and heat |
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Term
| Why do stars get progressively hotter as they use up their fuel? |
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Definition
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Term
| How hot must the interior of the sun be? |
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Definition
| In order to hold up against gravity - must be about 10 m kelvin |
|
|
Term
| What does the sun's massive internal T imply? |
|
Definition
| That all atoms are fully ionized into plasma (even Uranium). The vigour of the collisions strips them all off |
|
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Term
| What is the consequence of complete ionization? |
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Definition
| the sun's interior is thousands of tiny fast moving nuclei in a sea of free electrons. Therefore, The gaseous sun acts like a perfect (or ideal) gas' and obeys particularly simple laws! |
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Term
| T/F We understand the interior of the sun and the remote stars better than we understand the interior of the earth |
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Definition
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Term
| How do we get neutrons stars, pulsars and black holes? |
|
Definition
| If some force can overcome the huge electric repulsion between electrons --> Then all atoms could be enormously compressed and dense close packed matter |
|
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Term
| how we do consider pressure like a police raid (3)? |
|
Definition
Pressure is made up by three things
Number of particles - number of policeman charging the door
The mass of each particle - how heavy each policeman is
Their Speed - how fast they each run at the door |
|
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Term
| What does pressure depend on? |
|
Definition
| Density of gas (number and mass of particles) and their speeds. |
|
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Term
| What does speed of a gas tell us? |
|
Definition
|
|
Term
| What did people think about the sun's reactions? |
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Definition
1) They are burning - ordinary chemical reactions (requires fuel)
2) They are slowly contracting using gravity to keep the sun hot (and progressively raise it's temperature) |
|
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Term
| Why could it not simply be burning? |
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Definition
| Because they don't have enough fuel to keep it the same for billions of years |
|
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Term
| Explain Kelvin Contraction? |
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Definition
| The slow steady shrinkage of the sun, with it's increasing self gravity, would keep it hot. However, the shrinkage would be immeasurably small over the span of recorded history |
|
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Term
| Why did einstein help solve the burning sun problem? |
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Definition
| The sun emits a lot of ergs of energy every second (4 X10^33). And by using E=mc2 we learn that the sun is converted its mass into radiant energy at a rate of 4 million metric tonnes a secnod (which is a tiny % of it's overall rate) |
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Term
| What does E=Mc2 say about the sun's potential life time?Why is that wrong? |
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Definition
| It has enough mass to last about 10 trillion years, but thats wrogn because not all of its mass will get converted to energy. However, if 10% does get converted, it will yield a potential life time of 10 billion years |
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Term
| Does the changing mass of the sun affect's the earth orbit? |
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Definition
| Weakens, but in a neglible fashion |
|
|
Term
| What is important about the sun's stability? |
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Definition
| An even luminosity is helpful for the long term stability of our climate and for life on earth. |
|
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Term
| waht do we already know about the sun's stability? |
|
Definition
| Persistence of life on earth already tells us that it's been stable for quite a while |
|
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Term
| Is the sun like a baloon or snowball? |
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Definition
| The sun returns to equilibrium in 15 minutes, therfore it's like the baloon in that it returns to form |
|
|
Term
| Why is the sun like a bicycle pump? |
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Definition
| When we compress the sun, it leads to increase pressure and thus increased temperature. This increased T leads to more thermonuclear reactions and thus more heat, and more pressure outwards, and it restores the size of the sun |
|
|
Term
| What happens if you expand the sun somewhat? |
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Definition
| The central temperature falls, fewer nuclear reactions, too little central pressure to withstand teh inward pull of gravity. thee sun quickly shrinks back to original configuration |
|
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Term
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Definition
| Yes, very slowly. It changes as it uses up it's fuel. But its only the same scale as doctor's not worrying about the slow buildup of plaque during a given blood pressure test. Over a short timescale, the sun won't change (like millions of years) |
|
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Term
| What happens to stars when they are really old? |
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Definition
| They run out of fuel, begin to vary in brightness, pulsating like a beating heart. Within a day, the stars could double in brightness |
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|
Term
| What is important about the binding energy curve? |
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Definition
| From H to Fe, all fusion reactions release energy. From Fe onwards, the curve slopes down and all fission reactions are exergonic. |
|
|
Term
| What's easier, fission or fusion? |
|
Definition
| Fission, because it doesn't require insanely high temperatures |
|
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Term
| What are the problems with fission? |
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Definition
| We do it in pickering like reactors, but it's toxic or long lived radioactive, and has many waste products. Positives, it doesn't use greenhouse gases and does not gobble up fuel supply |
|
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Term
| Describe the process of neutron fission? |
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Definition
| Control is the key! you need to send one neutron at a nucleus, and then it begins to decay by sending off more neutrons. these sent off neutrons begin the process of decay for others atoms. so really, its a bomb where one thing leads to detenation of the others |
|
|
Term
| Why is it hard to have fusion reactors? |
|
Definition
| How do you contain a million degree gas? |
|
|
Term
| Why do you need high T for fusion |
|
Definition
| There needs to be a force to voercome the electromagnetic repulsions between nuclei. AT high speeds nuclei come close enough together for teh strong force to bind them together |
|
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Term
| Why are atomic bombs uncontrolled? |
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Definition
| You only need a critical msass of material close together. A supercritical mass leads to runaway reactions caused by escaped neutrons |
|
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Term
|
Definition
| They use fission reactions to create the neccessary heat for H fusion to occur. They release much more energy (when you consider the binding energy curve) |
|
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Term
| Why don't the reactions in the sun need to be confined? |
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Definition
| The enormous self gravity of the sun holds it together. There is no way for the fuel to escape so the nuclear reactions just keep tickign wawy in the hot central regions. |
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Term
| Why does the PP chain happen the way it does? |
|
Definition
| Because multiple protons colliding at the same time is nearly impossible, but just two colliding into each other is more likely. So it happens in steps in order to increase frequency |
|
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Term
|
Definition
| Two protons combine - forms a deuteron. The proton fusion leads to release of a positron through Beta decay. Then another proton is added (He isotope). Then two He isotope fuse (and remove two more protons) to from a full helium nucleus. In the end, its 4 protons forming a helium nucleus and it releases a ton of energy |
|
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Term
| How do we form neutrinos? |
|
Definition
| Convert a neutron to proton (get also an electron), but they don't follow law of conservation of linear momentum. Neutrino is hypothesized molecule that follows classical physics (and has be proven to exist). Note a positron is created when going the other way, from proton to neutron (also to keep charge) |
|
|
Term
| What is the antimatter particle of an electron? |
|
Definition
|
|
Term
| What happens when electrons and positrons meet? |
|
Definition
| They will anihilate each other and their mass is converted into pure radiant energy (via gamma rays) |
|
|
Term
| What is the practical use of Positrons? |
|
Definition
|
|
Term
|
Definition
| Essentially, you give a radioactive tracer. The tracer may get bound in up in cancerous cell (With high metabolic activity) and begin to decay. It's decay will produce positrons, who will immediately annihilate electrons. the subsequent Gamma rays produced can leave directly through the skull without interfering with matter, and can be detected. The manner in which they exit the body can be examined and a better analysis of the tumorous body can be created |
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Term
| What is the slowest link in the PP process? |
|
Definition
| the first one! an average proton takes 14 billion years to combine with another one .Conversely, deuterium is consumed almost instantaneously |
|
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Term
| Why are there different times in the PP process? |
|
Definition
| Because there are different probabilities of interacting (more like to get two larger masses than two smaller ones) |
|
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Term
| Because of the time each step takes in the PP process,what do we know? |
|
Definition
that a typical hydrogen nucleus has a long life in the core of the sun
There will be very little deuterium because it gets consumer so quickly once it is created |
|
|
Term
| Is the PP cycle the only way we get energy (heat)? |
|
Definition
| No, there are many other small PP chains (including BE, Li and B) not to mention the CNO cycle |
|
|
Term
| When do we get CNO cycles? |
|
Definition
| When stars have the heavier atoms presents, they can form the independant reaction cycle |
|
|
Term
| Whats the net effect of the CNO Cycle? |
|
Definition
|
|
Term
| What do C,N,O act as in the CNO cycle? |
|
Definition
| They act as modified catalysts because they speed up the reaction cycle but they themselves are left unchanged |
|
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Term
| Why is it harder to do the CNO cycle than the PP cycle? |
|
Definition
| You have to slam a porton into a nucleus of C or N ,rather than into anotehr proton. C and N have lots of protons, and therefore there is a large amount of electrostatic repulsion |
|
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Term
| Becuase of the repulsion between a C and a proton, what is required for the CNO cycle? |
|
Definition
| Lots and lots and lots of heat. In fact, the CNO cycle is dependnat to the 17th factor on Temperature, where the PP cycle is dependant to the 4th factor. On hotter planets, you get more of the CNO cycle |
|
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Term
| What are two problems we face when examinig the reactions in the sun? |
|
Definition
1) WE can't see into the centre of the sun
2) The brightness of the sun now only tells us how vigorous the reactions were some time ago |
|
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Term
| Why do photons take so much longer to leave the sun's centre than expected? |
|
Definition
| They perform a random walk, essentially bouncing off of everything and anything on their way out |
|
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Term
| Because we can't test photons, what do we do to probe the sun's interior? |
|
Definition
| The photon does a random walk, therefore it doesn't comes straight out of the deep interior. We need somethings that's much more direct. OR we can use seismic stud to measure the ways in which the sun is vibrating |
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Term
| How did we discover neutrinos? |
|
Definition
| First theoretically. WE know that a neutron forms a proton and electron. However, they move in similar directions (which would disregard the laws of conservation of momentum) so a third particle has to be formed (A neutrino) to balance out this equation |
|
|
Term
| What are the characteristics of a neutrino? |
|
Definition
| Uncharged, low mass, and elusive (barely interacts with other matter) |
|
|
Term
| Which two ways are neutrinos formed? |
|
Definition
In spontaneous beta decays (like uranium)
and in nuclear reactions (either in reactors or naturally in the sun) |
|
|
Term
| What is the main problem with neutrinos |
|
Definition
| It seems impossible to detect them. Though they are not rare, they travel through all matter (and the earth) |
|
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Term
| We had to prove neutrinos existed, how did we do this? |
|
Definition
| First, we used nuclear reactors and examined what happened when we turned them on and off (because nuclear reactors produced neutrinos). We attached a specialised detector that can see a tiny fraction of them (and in 1956 this was successful) |
|
|
Term
| What are the issues with finding solar neutrinos? |
|
Definition
| We have to eliminate all otehr sources of noise, the things that aren't the sun but may trigger a detector |
|
|
Term
| Who first tried to detect solar neutrinos |
|
Definition
|
|
Term
| How did ray davis experiment work? |
|
Definition
| He created a tank containing 100,000 gallons of cleaning fluid deep in a mine. Then he flooded the chamber with water before starting to detect neutrinos. Rarely, a neutrino hits a chlorine and converts it to argon. Then, after a few months, you collect th eargon and determine it's relative prevalence. |
|
|
Term
| What was unexpected about the ray davis experiment? |
|
Definition
| We only got 40% of the amount of neutrinos that we predicted |
|
|
Term
| What was not ideal about the experiment (4)? |
|
Definition
| Not time sensitive, no directionality, there are more efficient ways to capture neutrinos, it captures only one kind of neutrinos |
|
|
Term
| could there possibly be fewer neutrinos? how? |
|
Definition
| If it was cooler, and could be held up not by pressure but by srong magentic fields and rapid rotation |
|
|
Term
| What about neutrino flavors? could that have affected the experiment? |
|
Definition
| Davis experiment was only set up to detect one type, but apparently they may mix and turn into other forms he didn't detect. |
|
|
Term
| What were two good recent neutrino experiements? |
|
Definition
| Kamiokande and the SNO experiment |
|
|
Term
| Describe the SNO experimetn |
|
Definition
| Enormous vessel filled with heav water. It's mae of transparent plastic. When a neutrino passes through, there is a chance it will interact with one of the deuterons. This will lead to an electron being ejected and moving in the same direction as the neutrino itself - and it will move faster than the speed of light in water. The photomultipliers detect the flash of light and indicate the directio nfrom which the neutrinos came. |
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Term
What was there directionality in the SNO?
Time discrimination?
Sensitivity? |
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Definition
| The flashlight cone points in the direction the neutrino was travelling. Teh photomultipiers record the precise moment the flash was seen, so we know how steady the neutrino rate was. And deuterons are quite efficient neutrino detectors, much better than Cl atoms in the ray davis experiment. SNO detected a few dozen per day, while ray davis got one per day. LAslty, they can detect all flavors of neutrinos |
|
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Term
|
Definition
| Helioseismology utilizes waves that propagate throughout the Sun to measure, for the first time, the invisible internal structure and dynamics of a star. |
|
|
Term
| What can you use doppler shifts for? |
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Definition
MEasure them at various points on the sun
Then you consider the overtones that are produced. |
|
|
Term
| What is does helioseismology do for us? |
|
Definition
| Confirms the correctness of the standard solar model, and resolves also the neutrino problems |
|
|
Term
| Describe some aspects of the sun solar activity? |
|
Definition
| Flares, sunspots, spicules, chromospheres |
|
|
Term
| What type of motion does the sun use? |
|
Definition
| Convective motion (heating through wind movement) |
|
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Term
|
Definition
| They are cooler than the surrounding regions |
|
|
Term
| Why don't sunspots collapse? |
|
Definition
| They do, but are temporarily held up by their different magnetic field! They come and go in an inconsistent manner |
|
|
Term
| Do chickenpox move about? |
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Definition
| No, and so do sun spots. Some appear first on the abdomen and then spread to alomst everywhere else on the body |
|
|
Term
| Describe the sunspot pattern? Why like this? |
|
Definition
They form in a given location, at a non-middle latitude, and then persist for a while. The new spots form later, but tend to be closer to the equator.
It forms like this because there is different rotational times for the equator than the poles. They exist on a rotational timescale. First you get the ones at the poles, and then some form at centre (not the same spots). Eventually, the magnetic field gets super tangles and resets (but reverse poles) every 11 years. So we should see the same sunspots every 22 years |
|
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Term
|
Definition
| Because of magnetic field lines |
|
|
Term
| What does the magnetic field do? |
|
Definition
| The ionised gas is not free to move with complete liberty in the magnetic field, and this resistance provides an extra 'buoyancy' |
|
|
Term
| How do we know sunspots are correlated with magentic fields? |
|
Definition
| the presence of the magnetic field is deduced from the behavious of absorption lines in the light emitted by the sunspot regions. The magnetic field there is several hundred times the strength of the overall field of the sun |
|
|
Term
| Why is there an 11 year periodicity? |
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Definition
The magentic fields get so scrambled that every 11 years they start over (but in opposite direction)
Actually a 22 year series |
|
|
Term
| What kind of magnet is the sun's magnet like? |
|
Definition
| Like a bar magent, where magnetic field lines move frmo bottom to top |
|
|
Term
| What are the long timescale effect of sunspots? |
|
Definition
| Only in the 1600s, the maunder minimum |
|
|
Term
|
Definition
| Because its an average star that is close by |
|
|
Term
| How bright does the average star look in comparison to the sun? But how far is that average star? |
|
Definition
about 1/10^12 as bright
about a million times as far away |
|
|
Term
| What does the average star brightness and distance tell us about the sun? |
|
Definition
| THat the sun is actually quite an average star |
|
|
Term
| How close is the nearest star? |
|
Definition
| 4.2 Light years (40 trillion km) |
|
|
Term
|
Definition
| Per average, they move at about 30km/sec. At this speed it would take about 30,000 years to reach the nearest star |
|
|
Term
| Would stars ever collide? |
|
Definition
| Yea, potentially they could. But more likely not. Because it would be so random. However, there are binary stars that interact and depend on each other. |
|
|
Term
| In what do stars "not ignore" another? |
|
Definition
| Each one moves under the combined gravitational influence of all the material in the Milky Way galaxy - the other stars, gas dust and dark matter |
|
|
Term
|
Definition
| Stars that are literally in contact and share a mutual gravitational orbit |
|
|
Term
| What is tangential motion? ANd radial motion? |
|
Definition
| Tangential motion is the changing of a star's position among the constellations. Radial motion is changes of the distance betweeen us and the star |
|
|
Term
| How do find radial velocity of a star? |
|
Definition
| It only requires one observation, by spreading the light out into a spectrum, then measuring the doppler shift of the absorption lines . |
|
|
Term
| Combining radial and tangential motion, what do we get? |
|
Definition
| We find out the sun's or the earths motion. |
|
|
Term
| Is colour affected by distance? |
|
Definition
| No, it always tells us the temperature of the stars |
|
|
Term
| Do cool stars look bluer or redder? |
|
Definition
| More red - longer wavelength and less energy |
|
|
Term
| What does a spectra of the stars tell us? |
|
Definition
| Doesn't tell us about compositional differences, but rather differences in temperature. O and B type stars are hot, and M type stars are cold |
|
|
Term
| Are all red stars actually super cool? |
|
Definition
| not necessarily. There might be fog that impairs the color. Though, this impairment only happens in one direction (makes the stars appear cooler) |
|
|
Term
| What can we study without knowing the distance of a star? |
|
Definition
Position and motion (radial/tangential)
Colour and T (spectra)
Composition
RAte of rotation, strength of magnetic field |
|
|
Term
What is the proper motion of a star?
why is it called proper? |
|
Definition
It is the vector between the sun's current position and the star's tangential motion (has nothing to do with radial velocity).
Proper because it is only supposed to based on the star alone. |
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