P7 Revision

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  • Created by: ElishaG
  • Created on: 22-06-16 17:33
What is a sidereal day?
The time taken for star to return to the same position in the sky.About 23 hours and 56 minutes.
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What direction do the sun and moon appear to move?
East to west.
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What is a solar day?
The time taken for the sun to appear at the same position in the sky.It's 24 hours.
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Why are solar and sidereal days different?
The Earth orbits the sun as well as spinning on its axis.Earth orbits in same direction as it spins-Earth needs to spin slightly more for sun to appear.
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How long does it take for the moon to appear in the same place in the sky?Why?
25 hours.The moon orbits the Earth in the same direction as the Earth is rotating.
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Why do we see slightly different stars each night?
Because as the Earth moves around the sun,the direction we face changes slightly each day.
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What is an Earth year?
The time it takes for the Earth to orbit the sun once.So on same day each year you should see same stars.
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Explain phases of the moon.
1)Moon reflects light from sun-only the half facing sun lit up.2)As moon orbits Earth,see different amounts of Moon's surface lit up.3)Full moon=whole of lit up surface facing Earth.New moon=dark half facing Earth.4)Rest of phases in between.
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When do eclipses happen?
When light from the sun is blocked.
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What are the 2 main types of eclipse?
Lunar and solar.
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Describe lunar eclipses.
1)As it orbits,moon can pass into Earth's shadow.2)Earth blocks sunlight from moon-no light reflected.3)Moon seems to disappear.4)Total lunar eclipse=no sunlight at all.5)Normally partial eclipse-some light gets to moon.
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Describe solar eclipses.
1)When moon passes between Sun and Earth it can block out sun.2)Some parts of Earth,Sun completely blocked-total solar eclipse.3)Some places only part will be blocked-partial solar eclipse.4)Some places not blocked at all.
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Why don't eclipses happen very often?
The moon orbits Earth at an angle so most of the time the moon isn't in the right place.
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Why do partial eclipses happen more often?
Because the sunlight just needs to be partially blocked.
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What are the positions of stars measured by?
Angles seen from the Earth.
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What 2 fixed positions do astronomers measure from?
The pole star and the celestial equator.
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What is the pole star?
A star that hardly appears to move as it's directly above the North Pole.
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What is the celestial equator?
An imaginary plane running across the sky,extending out from the Earth's equator.
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What are the 2 angles used to measure positions in the sky called?
Declination and Right Ascension.
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What is declination?
Celestial latitude,measured in degrees.
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What is right ascension?
Celestial longitude(how much across) measured in degrees or time(360 degrees in 24 hours).
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Which direction does right ascension increase in?
The further east you go.
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What do all planets in the solar system do?
Orbit the sun in the same direction but at different speeds.The closer to the sun,the quicker it is.
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What are the 'naked eye' planets that can be seen without a telescope?
Mercury,Venus,Mars,Jupiter and Saturn.
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How can you track a planet as it goes across the sky?
Every night at the same sidereal time,note down position of planets.
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What direction do the planets travel in in the sky?
West to East.
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What is retrograde motion?
When a planet seems to change direction and go the other way,making a loop or squiggle and then carries on as normal.
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What planets does retrograde motion happen with?
Mars to Neptune.
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Why does retrograde motion occur?
Because both the planet and Earth are moving around the sun-we see the motion of the planet relative to Earth.
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How often does Mars appear to change direction?
Every 2 or so years.Slower moving planets 'change direction' less frequently.
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What is the speed of wave affected by?
The density of the things it's travelling in.
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What happens to a wave when it crosses a boundary between 2 substances?
The wave changes speed.
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What happens to a wave if the speed changes?
The wavelength changes.
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What is refraction?
When a wave changes direction as a results of change in speed and wavelength.
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Explain what happens when a light wave hits a boundary 'face on'.
It slows down,has a shorter wave length but the same frequency and travels in the same direction.
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Explain what happens when a light wave meets a different medium at an angle?
Part of the wave hits the boundary first and slows down but another part carries on at the faster speed for a while so that when it hits the medium the wave has been refracted.
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Which lens uses refraction to focus light waves to form and image?
Convex or converging.
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Explain how a converging lens uses refraction.
1)As light ray hits lens and moves from air to glass,it slows down-causes light ray to bend towards 'normal'(Line at right angles to boundary where ray enters or leaves).Continued...
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Converging lens and refraction continued.
2)Speeds up and bends away from normal as it goes from glass to air on other side.
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What does the curvature of a lens mean?
All the parallel rays hitting different parts of the lens are bent towards same focal point where an image is formed of whatever light is coming from.
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True or false-Different wavelengths of light refract by the same amount?
False-different wavelengths refract by different amounts.
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What happens to white light as it enters a prism?
It disperses(spreads out) into its different colours.
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What does a rectangular prism have?What does this mean?
Parallel boundaries.Rays bend one way as they enter and bend back again by the same amount as they leave.Light leaving glass is parallel to light entering it,so white light emerges.
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What are triangular prisms like?
Boundaries aren't parallel so different wavelengths don't recombine so you get a spectrum(rainbow).
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A converging lens is convex, what does this mean?
It gets fatter towards the middle,causing light to converge(come together) to a focus.
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What do all lenses have?
A principal axis,a line that passes straight through the middle of the lens.
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What is the focal point of a lens?
Where waves initially parallel to the principal axis meet(all lenses have a focal point in front and behind the lens).
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What is the focal length of a lens?
The distance between the middle of the lens and its focal point.
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What is focal length related to?
Power.The more powerful the lens,the more strongly it converges parallel rays of light,so the shorter the focal length.
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What is the power of a lens measured in?
D or dioptres.
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What can you do to a lens to make it more powerful?
Make it have a more strongly curved surface.
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Explain how to draw a point source ray diagram.
1)Mark focal point on principal axis.Draw 3 parallel rays from source(e.g star) one to centre,one towards top and one towards bottom.Only draw rays to middle of lens.2)Middle ray not refracted-extend past focal point.Continuedd.
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Point source ray diagram continued..
3)Draw top and bottom rays to meet middle ray above or below focal point-image formed at this point.
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Explain how to draw an extended source ray diagram.
1)Treat 2 opposite edges of object as point sources.2)Parallel rays will meet in line with or on focal point.3)Real image formed between 2 points where rays meet.
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What is a simple refracting telescope made up of?
Two convex lenses with different powers.
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What are the names of the 2 lenses that make up a refracting telescope?
Objective lens and a more powerful eye lens(or eye piece).
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What does the objective lens do?
Collects the light from the object being observed and forms an image of it.
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What does an eyepiece do?
Magnifies the image so we can view it.
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Explain the positions of the objective and eyepiece lenses.
Lenses aligned to have same principal axis and are placed so focal points are the same.
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What is light from far objects in space like when it reaches Earth?
Light rays effectively parallel.
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What does the objective lens do to these parallel rays?
Converges them to form a real image between 2 lenses.
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What does an eye piece do to the real image?
Much more powerful than objective lens (more curved).Acts as a magnifying glass on the real image and makes it a virtual image-where the light appears to have come from.
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What do most astronomical telescopes use instead of a convex objective lens?
A concave mirror-shiny on inside of curve,parallel rays reflect and converge.
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Describe telescopes with concave mirrors.
1)Concave mirrors like portion of sphere.Centre of sphere=centre of curvature.2)Centre of mirrors surface called vertex.3)Halfway between centre of curvature and vertex,is focal point-all lie on axis.Continued..........
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Telescopes with concave mirrors continued....
4)Rays parallel to mirror's axis e.g. those from a distant star reflect and meet at focal point.5)Can form a magnified image by putting a lens near focal point to act as eyepiece.
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What do waves do when they pass through a gap or past an object?
Spread out(diffract) at the edges.
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What does the amount of diffraction depend on?
The size of the gap relative to the wavelength of the wave.The narrower the gap,the longer the wavelength,the more the wave spreads out.
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What is the diameter of the objective lens called?
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When is a telescope with a huge objective lens (or mirror) used?
When an object is distant and faint-only small amount of radiation reaches us.The bigger the aperture is,the more radiation can get into the telescope so a better image is formed.
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Why do many telescopes have a concave mirror instead of a lens?
1)Large lenses is difficult and expensive.2)Easier to make big mirrors accurately.
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Why do images in telescopes blur?
Radiation entering a telescope spreads out at the edges of the aperture.
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What must aperture size be larger than?
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Why must aperture size be larger than the wavelength?
Because otherwise the point source would be dim and surrounded by rings that get dimmer the further away from the image they are.
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What is a diffraction grating like?
Has very narrow slits-small enough to diffract light.
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What happens when white light passes through the gaps in a diffraction grating?
Different wavelengths of coloured light are all diffracted by different amounts
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What does the diffraction of white light create?
A spectrum of different coloured light.
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What can astronomers use these spectra for?
To analyse the light coming from stars.
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What can the distance to nearby stars be measured by?
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What is parallax?
An apparent change in position of an object against a distant background.Makes closer stars appear to move relative to distant ones over the course of a year.
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What is parallax angle?
Half the angle moved against distant background stars over 6 months(opposite ends of Earth's orbit).The nearer an object is to you,the greater the angle.
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What is the parallax angle normally measured in?
Arcseconds. 1 arcsecond= 1".
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How many degrees is in an arcsecond?
1 arc second= 1/3600 degrees.
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What is parallax useful for?
Calculating the distance to nearby stars.Smaller the parallax angle,the more distant the star is.
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What unit of distance do astronomers usually use?
Parsecs. 1 parsec= about 3 light years.
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What is a parsec?
The distance to a star with a parallax angle of 1 arc second.
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What are distances between stars (interstellar distances) normally like?
A few parsecs.
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How can you calculate the distance to a star in parsecs.
Distance(pc)= 1 DIVIDED BY angle(arcsec).
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What is another word for luminosity?
Intrinsic brightness.
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What does intrinsic brightness of a star depend on?
The size and temperature.The bigger and hotter it is,the more energy it gives out,so the brighter it is.
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Why do stars look dimmer as you move away from them?
Because the energy spreads out through space.
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What does the observed intensity of a star seen on Earth depend on?Give an example.
Its luminosity and how far away it is from Earth.E.g. if 2 stars had the same luminosity but one was further away,the more distant star would look dimmer.
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What are Cepheid variable stars?
Stars that pulse in brightness, they get brighter and dimmer over several days.
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What is how quickly Cepheid variable stars pulse linked to?
Their luminosity,the greater the luminosity, the longer the time between pulses.
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How do astronomers work out the distance to Cepheid variable stars?
By comparing the luminosity (worked out by time between pulses) and the observed brightness.
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What shape is the Milky Way galaxy?
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How do we see the Milky Way galaxy from Earth?
As a bright strip of stars (wee see it side on).
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How many stars are in the galaxy?
Sun is 1 in 10(11).
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What were the names of two scientists who had a debate about the size and structure of the Earth?
Curtis and Shapely.
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What was the Curtis-Shapely debate over?
Faint,fuzzy objects called nebulae seen though telescopes,debate over what they were.
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What was Curtis' argument?
1)Thought universe made up of many galaxies.2)Thought our galaxy was about 10,000pc across with the sun close to the centre.3)Spiral nebulae were other,distant galaxies separate to Milky Way.
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What was Shapely's argument?
1)Thought univese was one huge galaxy 100,000pc across.2)Thought sun and solar system were far from centre of galaxy.3)Believed nebulae were nearby clouds of dust and gas and were part of Milky Way.
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Who was correct?Why?
Both.Shapely-Solar system far from centre of galaxy.Curtis-Said there were many galaxies and that spiral nebulae are far away.
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Why was the debate only settled ten years later, in the 30's?
Because there were better telescopes.
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Who helped to solve the Curtis-Shapely argument?
Hubble with his observations of the Andromeda nebula.
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How did Hubble do this?
He used images taken from the largest telescope at the time-found spiral shaped nebulae contained stars,some Cepheid variables.
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How did Hubble calculate the distance to the Andromeda galaxy?
By working out the distance to the Cepheid variables ,using their brightness and pulse frequency.
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How far away did he discover the Andromeda galaxy was?
2.5 million light years away-found similar results with other nebulae.
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What do astronomers use to measure distances to objects outside the Milky Way?
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What is the distance to the nearest spiral galaxy?
0.8 Mpc.
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What is red shift?
When a galaxy is moving away from us the wavelength of light becomes redder.
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How can you work out the recession velocity(how quickly it's moving away)?
By seeing how much light has been red-shifted. The greater the red shift,the greater the speed of recession.
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What pattern about red shift did Hubble find?
The more distant the galaxy,the faster it moves away from us.
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What is the Big Bang theory?
All matter and energy was compressed into a small space then exploded 14,000 million years ago and has been spreading out since.
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What is the value of Hubble's constant?
2x10(-18)s(-1) or 70km/s per Mpc.
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What has given us better values of Hubble's constant?
Cepheid variable stars.
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What does the kinetic theory say?
That gases consist of very small particles.
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Describe gases.
Particles constantly moving in completely random directions.Constantly collide with each other and the walls of the container they're in.When they collide,they bounce.Gases mostly empty space.
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What do you do if you increase the temperature of something?
You give particles more kinetic energy-they move around faster and vibrate more.
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What is the coldest anything can ever get?
-273 degrees.(Absolute Zero).
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What scale starts at absolute zero?
Kelvin-starts at -273 and a change of 1 degree is 1 Kelvin.
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How do you convert from Celsius to Kelvin?
Add 273.
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How do you convert Kelvin to Celsius?
Minus 273.
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What does anything that's moving have?
Kinetic energy.
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What happens if you double the absolute temperature(in Kelvins)?
You double the average kinetic energy of the particles.
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How is temperature and KE linked?
The temperature of a gas in Kelvins is proportional to the average kinetic energy of its particles.
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When do gas particles create an outward pressure?
When they collide with the container walls and exert a force on them.
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Why will the pressure decrease if you put the same amount of gas in a larger container?
There will be fewer collisions.
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What is the volume of gas inversely proportional to?
Its pressure at a constant temperature.
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What does the pressure of a gas depend on?
How fast the particles are moving and how often they hit the walls of their container.
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How does heating a gas affect its pressure?
If a gas is heated,particles move faster and kinetic energy increases.Means,partcles will hit container walls harder and more often,increasing the pressure.
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What is pressure proportional to?
Absolute temperature-doubling the temperature(K) doubles the pressure.
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What happens if gas stays at constant pressure and is heated?
Its volume increases-molecules are further apart so are less frequent but with more force.
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What is volume proportional to?
Absolute temperature.Doubling the temperature (in K) ,doubles the volume.
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What is nuclear fusion?
When two nuclei fuse to create a large nucleus.
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Which elements fuses in stars?
Hydrogen to make helium.
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What happens when the nuclei fuse?
Energy is released when lighter nuclei fuse to make heavier nuclei up to the size of an iron nucleus.
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When can the nuclei fuse?
If the nuclei are brought very close together-high temperatures and pressure needed.
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How can you calcuate how much energy is released during nuclear fusion(or fission)?
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What is a positron?
A postive electron that conserves charge.
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What do all hot objects like stars emit?
Radiation-continuous waves of frequencies.
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What is the peak frequency?
The frequency emitted the most.
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What does peak frequency depend on?
Temperature.The higher the temperature,the more energy the photons will have so the higher the peak frequency.
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What else depends on temperature?
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If a star is red,what do we know about it?
It has a low frequency and is cool.
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If a star is blue,what do we know about it?
It has a high frequency and it hot.
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What is ionisation?
When electrons gains enough energy to be removed from the atom.
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What is absorption spectra?
1)At high temperatures,electrons jump into higher energy levels by absorbing radiation.2)Only certain energy levels an electron can occupy,electrons absorb particular frequency of radiation to get to a higher energy level.Continued...
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Absorption spectra continued...
3)You can see this if a continuous spectrum of visible light shines through a gas.4)Electrons in as absorb certain light frequencies,making gaps in spectrum that appear as dark lines.
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What is emission spectra?
1)Electrons unstable in higher energy levels so tend to fall from higher to lower levels,losing energy by emitting radiation of particular frequency.2)Gives series of bright lines formed by emitted frequencies.
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True of false-energy levels are different for each element?
True.So each element has its own line spectrum.
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Explain how stars are created.
1)Born in cloud of dust and gas(mostly hydrogen and helium).2)Gravity causes dense clouds to contract slowly into clumps.3)When clumps dense enough,cloud breaks into protostars.4)Protostars collapse under gravity-reducing in volume.Continued.....
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How stars are created continued....
Protostars reduce in volume,increases pressure and temperature.5)Temperature reaches few million degrees so fusion starts.6)Releases enormous energy amounts and creates outward pressure to stop gravitational collapse.7)Star in main sequence stage.
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What is the core of a star like.
1)Most fusion takes place in centre.2)Pressure from weight and rest of star makes core hotter and denser than everywhere else.3)Nuclei in core close enough to fuse.
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What is the surface (photosphere) of a star like?
1)Outer region of star where energy is radiated into space.2)Energy released from fusion in core transported by photons and convection currents so surface of star.3)This is part of sun we see from Earth.
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When does a star stop being a main sequence star?
When it runs out of hydrogen in the core.
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What happens when a star runs out of hydrogen?
1)Swells up to become red giant or supergiant star.
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If a star is large what is the temperature like?
Hot.The larger a star is, the hotter the core,the heavier the nuclei it can fuse.
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What happens to low mass stars at the end of the main sequence stage?
1)Becomes red giant.2)Red giant doesn't have enough mass to compress core-no more fusion.3)Outer layers thrown into space.4)Core shrinks to become hot,white dwarf.5)No fusion in white dwarf star so it gradually cools and fades.
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What happens to high mass stars at the end of the main sequence stage?
1)Becomes red supergiant.2)Have enough mass to increase pressure of core so larger nuclei can be fused.3)Each time element becomes depleted,core shrinks until it's hot enough for more fusion.4)Happens until most fused into iron.Continued.........
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High mass stars continued.....
5)Red supergiants can't fuse iron so core collapses.6)Star explodes as supernova-creating nuclei with masses greater than iron.6)Core collapses to form neutron star OR if there's enough matter,a black hole-light can't escape.
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What is the Hertzsprung-Russell diagram?
A graph that shows if you plot luminosity against temperature on a graph,different types of stars group together.
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What are the advantages of computer controlled telescopes?
1)Can program telescope to track object.2)Can easily scan large areas of sky.3)More precise.4)Telescopes in remote places can be controlled.5)Can control many telescopes to face same direction.6)Can view telescopes around globe.Continued...
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Advantages of computer controlled telescopes continued...
7)Can record and process data.8)Can have telescopes in space.
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Explain scientific beliefs on other life in the universe.
1)Believe necessary conditions can be found on other planets or moons.2)Searching for planets outside solar system.3)Evidence of planets orbiting nearby stars-likely to be more.4)Probably life in universe.5)No evidence yet.
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Why do astronomers need accurate measurements?
So that they can understand what's going on in space.
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Why can the atmosphere cause problems for astronomers?
1)Atmosphere only lets certain wavelengths of EM radiation through and blocks others.2)Some waves e.g. radio pass through atmosphere easily but Visible light is badly affected.3)Light gets refracted by water in atmosphere-blurs images.Continued..
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Atmosphere problems continued...
5)Light can be absorbed by dust particles in air.
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Why are sites for observatories picked very carefully?
To minimise the problems caused by the atmosphere.
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What is another solution to overcome the problems caused by the Earth's atmosphere?
Put a telescope in space.
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When was the first space telescope launched?What is it called?
1990. Called the Hubble-can see objects billion times fainter than you can see looking at sky.
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What are bad things about having telescopes in space?
1)Getting it to space safely is hard.2)Difficult to get repair men there.3)Expensive.
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Why is most astronomy still done with Earth-based telescopes?
1)It is cheaper and easier to build and maintain.2)Good techniques developed to remove effects of atmosphere.3)Easier to get time slot in Earth telescopes as there are lots.
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What are space programmes?
Projects to send people,probes and telescopes into space.
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True or false-Space programmes are quite cheap?
False-they're very expensive.
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Why is the funding for space programmes never guaranteed?
Governments have to pay for defence,healthcare and natural disasters.
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What are many countries space programmes like?
They're linked so cut-backs in one country can have a knock-on effect on the others.
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Why is it good for countries to work together on space programmes?
Because they can share expertise and the cost.
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What are 2 examples of countries working together?
1)The ISS- US and 15 countries.Each country provides different parts.Most expensive and largest science project in history.2)European Extremely Large Telescope-Astronomers across whole of Europe-based in Chile.Too complex and expensive for 1 country.
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What are 4 reasons that are considered when deciding where to build observatories?
1)Optical(visible light).2)Atmosphere.3)Refraction.4)Clouds.
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Explain optical.
1)Observatories often put in remote locations e.g. Canary Islands.2)Idea to avoid man-made pollution as well as dust from affecting observatories.
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Explain atmosphere.
1)Want as little atmosphere between observatory and telescope as possible-minimise blurring.2)Observatories built high up e.g. mountains where atmosphere is thinner e.g. Hawaii.
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Explain refraction.
1)Water in atmosphere can cause problem by refracting light.2)Dry location with low atmosphere pollution good e.g. Australia and Chile.
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Explain clouds.
1)Block view of sky.2)Telescopes built in places with lots of cloudless nights.
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What are 4 other factors that need to be considered?
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Explain cost.
Observatories aren't cheap-building,running and eventually closing.
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Explain access.
Site will need roads to get equipment there as well as electricity.Some places too hard to get to.
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Explain environment.
Scientists have to be careful that building works-damage environment as little as possible.
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Explain social.
Always going to be people to work at telescope-need water,accommodation,electricity,shops etc.Expensive to provide.Some areas benefit community-provide jobs maintaining and building observatory.
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Card 2


What direction do the sun and moon appear to move?


East to west.

Card 3


What is a solar day?


Preview of the front of card 3

Card 4


Why are solar and sidereal days different?


Preview of the front of card 4

Card 5


How long does it take for the moon to appear in the same place in the sky?Why?


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