P7 -

A brief overview of the whole of the P7 module. 

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  • P7
    • The earth rotates west-east.
      • A day is just under 24 hours.
    • A side-real day - the time it takes for earth to rotate 360 on it's axis.
      • A solar day - noon to noon, AKA 24 hours.
        • A side real day is shorter than a solar day because as the sun rotates, it also orbits the sun.
    • The position of an astronomical object is measured in angles.
      • The angles of declination and right ascension.
        • A star with a positive declination will be visible from the northern hemisphere and a star with a negative declination will be visible from the southern.
    • Planets move with retrograde motion, they can be seen to move compared to the stars in the background which appear still.
      • The Earth's small orbit than other planets, causes it to ovetake the outer planets at different times of the year which makes them look like they're slowing down and going in reverse.
    • The lunar cycle is the appearance of the moon during it's 28 day cycle.
    • Light, water and sound waves can be refracted. When they cross bewtween one medium to another, the frequency will stay the same however the wavelength can change. this change can lead to a change in a wave speed which can cause the waves to change direction. Thus being refracted.
      • Diffraction occurs when the wave passes through a narrow gap that is similar to/ smaller than the wave itself and the waves spread out from the edges.
        • Radiation is diffracted by the aperture of a telescope to make the images sharper.
    • The spectra observed from elements in stars belonging to distant galaxies, indicates that light is 'red shifted.' The further away a galaxy, the more red shifted the light.
    • Extrasolar planets are planets that orbit a star other than the sun.
    • When electrons are removed from an atom it's called ionisation. When electrons move inside an atom it causes it to emit radiation of specific frequencies. This is called line spectra. Different elements have different line spectra.
      • By comparing a star's spectrum to an emissions spectrum, it will help show which elements are in the star. As the element's spectra will match the stars.
    • Two optical and infrared astronomical observatories are; Royal observatory (largest reflecting telescope in UK) and the largest reflecting telescope in the world, Mauna Kea observatories.
      • The factors that often influence where these telescopes go are; high altitude (less atmosphere to absorb light) isolated location (less pollution to interfere with the signal) equatorial location (the best view of solar eclipses) and frequent clear skies. Other factors to be considered are; cost, environmental and social impact and working conditions.
    • Space telescopes (eg hubble) take pictures of the universe. Advantages of these telescopes is that they're not affected by the absorption and refraction of light from the earth's atmosphere. And can use the parts of the EMS normally absorbed by the atmosphere. However there are some disadvantages, like, they're expensive to make and run and there's uncertainties about space programmes e.g launch delays.
      • When controlling telescopes with computers the telescope can be tracked to follow certain objects, it can be isolated in a place that is normally difficult or impossible for humans to get to, it can be programmed to find precisely any star, the computer can directly record data.
      • Telescopes can be accessed through computers, directly at the site or through the internet. School's in the UK can access the Royal Observatory on the internet.
  • A solar eclipse is when when the moon 'covers' the sun, creating a shadow on Earth.
    • A lunar is when the Earth 'covers' the sun and causes a shadow on the Moon.
      • An eclipse only occurs when the moon passes through the ecliptic path.
    • P7
      • The earth rotates west-east.
        • A day is just under 24 hours.
      • A side-real day - the time it takes for earth to rotate 360 on it's axis.
        • A solar day - noon to noon, AKA 24 hours.
          • A side real day is shorter than a solar day because as the sun rotates, it also orbits the sun.
      • The position of an astronomical object is measured in angles.
        • The angles of declination and right ascension.
          • A star with a positive declination will be visible from the northern hemisphere and a star with a negative declination will be visible from the southern.
      • Planets move with retrograde motion, they can be seen to move compared to the stars in the background which appear still.
        • The Earth's small orbit than other planets, causes it to ovetake the outer planets at different times of the year which makes them look like they're slowing down and going in reverse.
      • The lunar cycle is the appearance of the moon during it's 28 day cycle.
      • Light, water and sound waves can be refracted. When they cross bewtween one medium to another, the frequency will stay the same however the wavelength can change. this change can lead to a change in a wave speed which can cause the waves to change direction. Thus being refracted.
        • Diffraction occurs when the wave passes through a narrow gap that is similar to/ smaller than the wave itself and the waves spread out from the edges.
          • Radiation is diffracted by the aperture of a telescope to make the images sharper.
      • The spectra observed from elements in stars belonging to distant galaxies, indicates that light is 'red shifted.' The further away a galaxy, the more red shifted the light.
      • Extrasolar planets are planets that orbit a star other than the sun.
      • When electrons are removed from an atom it's called ionisation. When electrons move inside an atom it causes it to emit radiation of specific frequencies. This is called line spectra. Different elements have different line spectra.
        • By comparing a star's spectrum to an emissions spectrum, it will help show which elements are in the star. As the element's spectra will match the stars.
      • Two optical and infrared astronomical observatories are; Royal observatory (largest reflecting telescope in UK) and the largest reflecting telescope in the world, Mauna Kea observatories.
        • The factors that often influence where these telescopes go are; high altitude (less atmosphere to absorb light) isolated location (less pollution to interfere with the signal) equatorial location (the best view of solar eclipses) and frequent clear skies. Other factors to be considered are; cost, environmental and social impact and working conditions.
      • Space telescopes (eg hubble) take pictures of the universe. Advantages of these telescopes is that they're not affected by the absorption and refraction of light from the earth's atmosphere. And can use the parts of the EMS normally absorbed by the atmosphere. However there are some disadvantages, like, they're expensive to make and run and there's uncertainties about space programmes e.g launch delays.
        • When controlling telescopes with computers the telescope can be tracked to follow certain objects, it can be isolated in a place that is normally difficult or impossible for humans to get to, it can be programmed to find precisely any star, the computer can directly record data.
        • Telescopes can be accessed through computers, directly at the site or through the internet. School's in the UK can access the Royal Observatory on the internet.
  • A convex lens is used to bend light rays inwards when passing through. If the rays are parallel when entering the lens, they are brought to a focal point when refracted.
    • The bigger the curve of the lens, the more powerful it will be.
      • To calculate the power of the lens you use this formula.         Power (dioptres) = 1 / focal length (metres)
  • A simple refracting telescope uses two convex lenses of different powers. the eyepiece lens (the one you look through) is higher power than the objective lens (the one that capture the parallel light rays.) The objective lens refracts the light rays to the eyepiece lens, which is the focal point and the eyepiece lens magnifies the rays/ the image.
    • An astronomical telescope uses a concave mirror instead of the objective lens. Concave mirrors reflect the light instead of capturing it and helps to focus. They're also a lot larger to can collect more light.
  • A magnified image will make the object appear closer than it is. This is because the angle of the light rays entering the eye is larger.
    • The increase in the angle is called angular magnification.
      • To calculate angular magnification you use.  Magnification = focal length of objective lens / focal length of eyepiece lens.
  • Parallax is the 'apparent' movement of an object. However it's normally the movements of the observer that cause the object to appear to be moving.
    • For example if you look at an object and close one eye and then the other. The object appears to move.
      • This occurs when stars appear to move in relation to other stars.
        • The parallax angle of a star is; the angle moved, against a background of distant stars, in six months, halved.
          • A further away object will have a smaller parallax.
            • Parallax can be used to measure interstellar distances. In the unit parsec (pc.)
              • A parsec is the distance to a star which has a parallax angle of one second per arc.
                • Mega-parsecs measure intergalactic distances.
                  • To calculate the distance of interstellar objects you use this formula; Distance (Parsecs) = 1 / Parallax angle (arcseconds)
  • Astronomers can measure distances of stars using their brightness. E.g. A closer star will appear brighter. However they don't necessarily give out the same amount of energy (have the same luminosity.)
    • Luminosity is dependant on size and temperature.
      • This means that how we see the intensity of a star, depends on it's luminosity and it's distance from earth.
        • A low luminosity star may seem duller even if it is very close to earth.
          • Astronomers can measure distances of stars using their brightness. E.g. A closer star will appear brighter. However they don't necessarily give out the same amount of energy (have the same luminosity.)
            • Luminosity is dependant on size and temperature.
              • This means that how we see the intensity of a star, depends on it's luminosity and it's distance from earth.
                • A low luminosity star may seem duller even if it is very close to earth.
    • A cepheid variable star, doesn't have a constant luminosity. It pulses which means its luminosity depends on the length of the pulse.
      • The changing frequency of pulses can be used to work out the distance of cepheid variable stars.
    • The Curtis-Shapley Debate, was a debate about the scale of the universe that happened in 1920. Between Heber Curtis and Harlow Sharpley
      • Curtis believed that the universe was made up of galaxies like ours and the fuzzy objects (originally called nebulae) were these distant galaxies.
      • Sharpley believed that the universe was one big galaxy and the nebulae were just nearby gas clouds within the milky way.
    • Edwin Hubble made an observation in the mid 1920s where he saw that the nebula he was observing was much further away than any star in the milky way. He found this by observing a cepheid star in the nebula.
      • This helped show the nebula was a distant galaxy. Now by observing cepheid stars, scientists can see that most nebulae are actually distant galaxies.
        • Now because of this astronomers have been able to measure the distance of the galaxies and determine the scale of the universe.
          • Hubble's discovery led to him finding that the universe was expanding. He found the further away a star was, the faster it was moving away.
            • Cepheid stars can be used to find the hubble constant (s-1 / kms-1 / Mpc-1) Which can help us find the speed of recession - how fast a star is moving away. We also use red shift for this.
              • Use this formulae; Speed of recession (km/s) = Hubble constant (s-1 / kms-1 / Mpc-1) x Distance (Km / Mpc)
    • Gas pressure is caused by the movement of gas particles. When the moving particles collide with one another or another object, they exert a force which is known as pressure.
      • The pressure is dependant on the number of collisions per second and the momentum of the particles. So when the volume is decreased the pressure increases as the is less space for the gas particles to move so more collisions.
        • The volume of gas is inversely proportional to the pressure when at a constant temperature. Pressure x volume = constant (temperature)
          • If a gas is heated up, the particles move faster. This leads to more collisions and a higher pressure. Which means the constant is the volume. Pressure / Temperature = Constant (volume)
    • When the temperature in a gas is reduced, the particles move slower which means the pressure falls. The particles eventually stop moving when the temperature is so cold. This is the absloute zero which is -273 degrees. Or 1 Kelvin (K)
      • To convert degrees to Kelvin you need to add 273.
    • A star has three main parts; the core (The hottest part where nuclear fusion takes place and photons are released) the convective zone (where photons are released again and carried to the photosphere by convection currents) and the photosphere (the outer layer where photons are radiated into space.
      • A 'red' hot object emits the majority of its energy in the red frequency range.The light frequency of a star can show how hot it is.
    • All stars begin as gas clouds (often hydrogen.) Gravity then pulls the clouds together to make them denser. The pull of the gravity increase the pressure and the temperature. The more gas that's pulled in, the greater the force of gravity. Once the gas is so compressed it gets hotter and denser to form something called a protostar. When the temperature and pressure is so high, the hydrogen nuclei fuse to form helium. This is called nuclear fusion. This is now known as a main sequence star.
      • Nuclear fusion mainly happens in the stars core. Nuclear fusion happens in main sequence stars. When stars leave the main sequence they become red giants.
        • In a red giant more fusions take place. helium fuses to form carbon, heavier nuclei are formed such as nitrogen and eventually oxygen. At each stage energy is released. In a very high mass star (bigger mass than the sun) the nuclei can be so heavy it can be up to and including iron and explodes as what is known as a supernova. This supernova leaves behind a neutron star or a black hole.
          • E=mc^2 is the equation used to calculate the energy released during nuclear fusion. E = energy. M = mass lost. And c = the speed of light in a vacuum.
    • The Hertzsprung- Russell diagram is a plot of temperature and luminosity of stars. To indentify regions where supergiants, red giants, main sequence stars and white dwarfs are located.
      • A low mass star that becomes a red giant but doesn't have a high enough mass to go past helium fusion will shrink to form a white dwarf. Where no nuclear fusion takes place. The white dwarf will gradually cool and fade.
    • Most telescopes are developed through international co-operation. This means cost is shared and knowledge can be shared. Astronomers can then 'book' time on the telescopes in other countries to see stars from different parts of Earth.

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