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| Question | Answer |
|---|---|
| What does the solar system contain? | the sun, planets, meteors, comets, moons, minor planets, and asteroids |
| What is a comet? | frozen rocks that orbit the sun in elliptical orbits |
| When can you see a comet? | comets have an ellipitical orbit and can only be seen when they are close to the sun which makes them heat up and emit light |
| What are meteors? | small pieces of rock that enter the atmosphere and burn up |
| What is another name for meteors? | shooting stars |
| What is the sun? | a star at the centre of the solar system |
| What are stars formed from? | clouds of dust and gas that are pulled closer and closer together by gravitational attraction |
| How did the sun form? | clouds of dust and gas were pulled closer and closer together by gravitational attraction |
| When did the sun form? | billions of years ago - the sun is around 5 billion years old and will last for another 5 billion years |
| Name the planets in order around the sun. | mercury, venus, earth, mars, jupiter, saturn, uranus, neptune |
| Where is the earth among the planets orbitting the sun? | third planet from the sun |
| Describe the orbits of the planets orbitting the sun. | they orbit around the sun in circular or near-circular orbits that are all in the same plane |
| What is the 'habitable' zone? | the zone around the sun where water can exist as liquid on the planet |
| What is a protostar? | a star forming because a concentration of gas and dust becomes hot enough to cause nuclear fusion |
| How does a protostar form? | the particles in the clouds of gas and dust are pulled together by their own gravitational attraction speeding up and becoming more and more concentrated |
| What happens when to turn a protostar into a star? | the protostar becomes denser, particles speed up and collide more, and its temperature increases so hydrogen atoms fuse to become helium nuclei releasing energy starting to shine |
| Name the process that combines hydrogen atoms to form helium nuclei. | fusion |
| How do stars acquire planets? | smaller objects are attracted to the star by the star to become planets that orbit the star |
| Why do stars radiate energy? | because hydrogen fusion in the core of the star releases energy |
| What is a star called during the principal part of its life? | a main sequence star |
| What keeps the fusion in the core of the star going? | fusion generates energy that keeps the core hot and keeps the process of fusion going |
| Why is a main sequence star stable? | the gravitational forces acting inwards are balanced by the forces from the radiation from the fusion acting outwards |
| When are the forces in the core of a star no longer in equilibrium? | when most of the hydrogen nuclei have been fused into helium nuclei |
| What is the heaviest known natural element? | uranium |
| What is the half life of uranium? | 4500 million years |
| What does the presence of uranium demonstrate about the origin of the earth and the solar system? | that the earth and the solar system must once have been part of a supernova |
| Name an element heavier than uranium? | plutonium |
| How is plutonium obtained? | plutonium is made by bombarding elements like uranium with high speed neutrons |
| Why is plutonium not found on the earth? | plutonium would have been present when the solar system was first formed but have long since decayed |
| Question | Answer |
|---|---|
| What defines that a star has reached the end of its main-sequence stage? | it runs out of hydrogen nuclei to fuse together at its core |
| What happens to a star when it reaches the end of its main-sequence stage? |
• it runs out of hydrogen nuclei to fuse together at its core • it becomes unstable • its core collapses • its outer layers swell out |
| What happens to stars about the same size or smaller than the sun? | they swell out, cool down, and turn red |
| What are stars that have turned red called? | red giants |
| What happens in a red giant? | helium and other light elements combine in the core fuse to form heaver elements |
| What happens to a red giant when there are no more light elements in the core? |
• fusion stops • no more radiation is released • the star collapses in on itself because of its own gravity • it heats up • it turns from red to yellow to white • it becomes a white dwarf |
| What is a white dwarf? | a white, hot, dense star smaller than its original size |
| What happens to white dwarfs? | they fade out, go cold, and become black dwarfs |
| List in order the stages in the life of a star the size of the sun |
• protostar • main-sequence star • red giant • white dwarf • black dwarf |
| What will the star become at the end of its life? | a black dwarf |
| What do stars much larger than the sun do at the end of their main-sequence? | they swell out to become red supergiants |
| What happens to red supergiants? |
• they collapse • the matter around the core, compresses the star more and more • the compression suddenly reverses • there is a cataclysmic explosion called a supernova • a supernova can outshine an entire galaxy for weeks |
| What is a supernova? | the explosion of a red supergiant after it collapses |
| List the stages in order in the life of a star much, much larger than the sun |
• protostar • main-sequence star • red supergiant • supernova • neutron star • black hole if enough mass |
| How is helium formed? | hydrogen nuclei are fused to form helium in stars |
| What happens in the core of stars like the sun? | hydrogen nuclei are fused to form light elements like helium and carbon |
| What happens in the core of a red giant? | it fuses helium and other light nuclei into larger nuclei |
| What are the largest nuclei formed in a red giant? | iron |
| Why is iron the largest nuclei formed in a red giant? | too much energy is needed |
| When are heavy elements formed? | when a massive star collapses then explodes as a supernova |
| Why can a massive star collapse form heavy elements in a supernova? | in a supernova, temperatures and pressures are extraordinarily high, much, much higher than in a star or red giant, creating the conditions to fuse lighter nuclei to form heavy nuclei |
| What elements are contained in the debris of a supernova? | all the elements from light to heavy |
| What happens to the debris from a supernova? |
• the explosion scatters the elements throughout the universe • new stars pull the debris together • some of the debris is pulled together to form new planets surrounding a star • planets made from the debris of supernova contain all the elements |
| How old is the sun? | 5000 million years old (half a billion years) |
| How long before the sun continue? | 5000 million years (half a billion years) |
| What will happen to the sun when it reaches the end of its main-stage? | it will become a red giant |
| How large will the sun become when it turns into a red giant? | the red giant will be greater than the orbit of mercury, venus and probably the earth |
| How will life on earth be affected as the sun ages |
• in 1.1 billion years, the sun will be 10% hotter triggering a greenhouse effect like the one that turned venus into what it now is • in 3.5 billion years, the sun will be 40% hotter causing the seas to boil, and all water vapor in the atmosphere to evapourate transforming the earth into a hot, dead world like Venus |
| What is left after a supernova explosion? | the explosion compresses the core into a neutron star |
| What is a neutron star? | an extremely dense object made up entirely of neutrons |
| What happens to a neutron star? | if the star is massive enough, the neutron star will become a black hole |
| Why is it known as a black hole. | the gravity of a black hole is so strong that nothing can escape from it, not even light |
| Question | Answer |
|---|---|
| What is the shape of the orbit of the earth? | it is almost circular |
| What are the shapes of the orbits of the other planets in the solar system? | they are ellipses or slightly squashed circles |
| What is the moon? | the man is a natural satellite that orbits the earth in a circular orbit |
| What is the force holding satellites in place around the earth? | the force of gravitational attraction between the earth and the satellite |
| In what direction does the force of gravity acting on a planet act? | towards the centre of the sun |
| What type of force is this gravitational force? | it is a centripetal force |
| Why is the gravitational force holding satellites around the earth a centripetal force? | because it acts towards the centre of the circle |
| What is the effect of the gravitational force on the movement of the satellite? | it changes the direction of the satellites velocity |
| How does the direction of the velocity compare with the direction of the force? | the velocity of a satellite is at 90 degrees to the force of gravity on the satellite |
| What is the resultant force on a satellite? | the centripetal force is the resultant force acting on a satellite as there are no other forces acting on it |
| What is the acceleration on a satellite in a circular orbit? | the acceleration is towards the centre of the orbit in the same direction as the resultant force |
| What is the effect of the acceleration on a satellite in a circular orbit? | it changes the direction of the velocity but not its magnitude |
| What work does the force do on a satellite? | none, because the force is at right angles to the direction of motion |
| What is the effect of the of the force on kinetic energy, velocity and speed |
• kinetic energy does not change • the direction of velocity changes but the magnitude of velocity does not change • the speed (also known as the magnitude of velocity) does not change |
| What happens to a satellite too close to the earth? |
• it gradually loses speed • it spirals inwards towards the earth • it eventually hits the earth |
| Why does a satellite too close to the earth lose speed? | because of atmosphere drag |
| What is meant by a satellite being in a stable orbit? | the satellite moves at a constant height above the surface of the earth i.e. its orbit does not move outwards or inwards with respect to the earth |
| What must a satellite do to move in a stable orbit? | the satellite must move at a particular speed |
| What happens to a satellite launched at too low a speed? | if the satellite is too slow, it will fall back towards the earth |
| What happens to a satellite launched at too fast a speed? | if the satellite is too fast, it will fly off into space |
| What happens to a satellite launched at the correct speed? | it will move in a circular orbit at a constant height and a constant speed |
| What is the effect on speed on distance for a satellite around the earth? |
• the greater the distance from the earth, the slower the speed needed for a stable orbit • the longer the satellite takes to orbit the earth |
| Why does a larger orbit reqire a lower speed? | the force of gravity is weaker when it is further from the earth |
| What is the effect on speed on distance for a satellite around the earth? |
• the greater the distance from the earth, the slower the speed needed for a stable orbit • the longer the satellite takes to orbit the earth |
| Why does a larger orbit require a lower speed? |
• the force of gravity is weaker when it is further from the earth so it does not need to travel as fast to maintain its orbit • the circumference of the orbit is smaller so the satellite moves slower to stay in orbit |
| State the properties of a communication satellite? |
• in an orbit of about 36 000km • with a period of 24 hours • stay above the same spot on the earth • this kinds of orbit is known as a geostationary orbit |
| List three uses of monitoring satellits? |
• weather forecasting • monitoring the environment |
| What is a monitoring satellite? | satellites that orbit the earth |
| What is a geostatianary satellite? | satellites they remain permanently about the same spot on the earth |
| How do the orbits of geostationary and monitoring satellites compare? |
• monitoring satellites are in much lower orbits than geostationary satellites • monitoring satellites orbit the earth every two to three house, while geostationary satellites remove in the same position above the earth |
| Question | Answer |
|---|---|
| Where is the sun in the solar system? | the earth is the third planet from the sun |
| Where is the sun in the galaxy? | the sun is a star on the outskirts of the Milky Way galaxy |
| What is a galaxy? | a very large collection of stars that are held together by the gravity between them |
| How many stars are there in the Milky Way? | about 100 billion stars |
| How large is the Milky Way? | it is about 100 000 light years across |
| What is a light year? | the distance that light travels in a year |
| How many galaxies are there in the known universe? | many billions |
| How far away are the furthest known galaxies? | about 13 billion light years away |
| How are stars and galaxies studied? | by examining the light that they produce |
| How is light split into a spectrum? | using a prism |
| What is used to determine if a star or galaxy is move away or towards the earth | the spectrum of light from the star or galaxy |
| How does the wavelength of light change with colour? | the wavelength of light increases from blue to red |
| What is red-shift? | the wavelength of waves is increased (shifted towards the red part of the light spectrum) because the star or galaxy is moving away from the earth |
| What is blue-shift? | the wavelength of waves is decreased (shifted towards the blue part of the light spectrum) because the star or galaxy is moving towards the earth |
| What determines have big the shift is? | the faster the star or galaxy is moving away or towards the earth |
| What did Edwin Hubble discover about the universe? |
• the light from distant galaxies was red-shifted • the further a galaxy is from earth, the bigger its red-shift |
| What did Edwin Hubble conclude from the evidence that he collected about galaxies? |
• the distant galaxies are mobing away from the earth • the greater the distance a galaxy is from the earth, the greater the speed at which it is moving away form the earth |
| What can be concluded from Hubble's work? | the entire universe is expanding |
| Question | Answer |
|---|---|
| Name the model used to explain the expansion of the universe. | the Big Bang |
| Describe the Big Bang? |
• space, time and matter were created in the Big Bang • the Big Bang was a huge explosion of a very small and extremely hot and dense region • the universe is expanding as a result of the Big Bang |
| What was the alternative explanation of the Big Bang? | the steady state theory |
| How is the expanding universe explained by the steady state theory? | the expansion was caused by matter entering the universe through white holes (the opposite of black holes) |
| What evidence demonstrated that the Big Bang model was the correct explanation? | the discovery of cosmic microwave background radiation (CMBR) in 1965 |
| What is the origin of cosmic microwave background radiation (CMBR)? |
• high-energy gamma radiation was produced just after the Big Bang • the gamma radiation produced has been stretched out to longer and longer wavelengths i.e. lower-energy radiation • the raidation is now microwave radiation |
| What will determine whether the universe expands forever? | the total mass of all the galaxies, how much matter is between them, and the space they occupy i.e. the density of the universe |
| How much of the mass of a galaxy is made up of the total mass of the stars in the galaxy | a small percentage |
| How do astronomers know that the mass of the stars is only a small percentage of the total mass of a galaxy? | the galaxy would spin much faster if the only mass in a galaxy was the mass of the stars |
| What other than the stars in the galaxy accounts for the mass of a galaxy? | dark matter |
| Why is it called dark matter? | because it can't be seen |
| What is the effect of dark matter on the mass of a galaxy? | it makes the average density of the universe much bigger |
| How does the density of the universe affect its expansion? |
• if the density is below a certain amount, the universe will expand forever - the Big Yawn • if the density is below a certain amount, the universe will eventually stop expanding and go into reverse - the Big Crunch |
| What has caused astronomers to conclude that the universe will expand forever? | observations of supernova in distant galaxies suggest that the distant galaxies are accelerating away from each other |
| What is puzzling about the galaxies accelerating? |
• there must a source of energy causing the acceleration • gravity is an attractive force so cannot be driving the acceleration • gravity is the only known force acting on the stars in a galaxy • the source of the energy causing the acceleration is unknown • the unknown source of energy is known as dark energy |
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