OCR 21st Century P1

Solar System
1. Diameters
  1. Earth-12,800km
  2. Sun- 1.4 million km
  3. Earth's Orbit- 150 million km
  4. Solar System- 9.09 billion km
  5. Milky Way- 100,000 light years
2. Distances
  1. Milky Way to Andromeda- 2.5 million light years away
    1. Sun to Proxima Centauri- 4.22 light years
  2. Light Years- The distance travelled by light in a year
    1. Light travels at 300,000km per second
    2. 1.3 seconds Moon--->Earth
    3. 4 years across Solar System
    4. 100,000 years across MW
    5. The finite speed of light means that very distant objects are observed as they were in the past, when the light we now see left them
  3. Parallax- the apparent shift of a star against more distant stars as the position of the observor changes. The further away a star is, the the less it appears to sift at two different intervals
    1. However parallax is only effective for nearer stars as at greater distances the shift is so small it isn't measureable
  4. Relative Brightness-the brighter a star, the closer it is providing that the comparative star is the same type
    1. light pollution and other atmospheric conditions interfere with observations of the night sky
3. 8 planets, many moons and asteroids orbit the sun in circular motions.
  1. Comets- large balls of ice and dust. Elliptical orbits
    1. Asteroids- Orbit the sun between Mars and Jupiter
4. Sun
  1. One of thousands of millions of stars in the Milky Way galaxy
    1. Fusion of hydrogen nuclei produces helium and masses of heat and energy
      1. Helium is then fused to make heavier elements such as carbon and oxygen
5. Origin
  1. 5000 million years ago a great swirl of dust and gas came together
    1. About 99% of that material became the Sun
      1. Gravity pulled the remaining particles into smaller clumps which continued to join to form planets
        As it formed, the Solar System gathered debris from previous generations of dead stars. Except Hydrogen and Helium everything on earth is made from stardust
6. Measuring Uncertainties
  1. First scientists had to measure the Earths orbit around the sun. Then they had to use parallax to measure the distance to nearby stars. After that had to use the brightness method to measure the distance to further stars. Another method involved Cepheid variables, which was needed to extend the measurements beyond the Milky Way
    1. Each method depended on the result of the previous one so the final results were uncertain.
      1. these methods have built-in assumptions E.g. the brightness method assumes the stars are the same type
        By making different measurements scientists estimated the size of the Universe
Universe
1. Big Bang- 14 Billion Years ago
  1. when astronomers look at light from distant galaxies, it is shifted to the red end of the spectrum. This is redshift and the amount of it shows how fast galaxies are receeding
    1. Speed of Recession= Hubble Constant * Distance
    2. The further away a galaxy is, the faster it is moving away
  2. A hot Big Bnag exp,lains why the the early Universe was 76% Hyfrogen and 24% Helium by mass
  3. The oldest stars (12 billion years) are younger than the 14 billion year old Universe.
    1. Earth= 4.5 billion years
2. the ultimate fate of the Universe is dif cult to predict because of dif culties in measuring the very large distances involved and the mass of the Universe, and studying the motion of very distant objects.
  1. If the Universe has a high mass, it's gravty may cause it to eventually colapse= Big Crunch
Rocks and Plate Tectonics
1. erosion, sedimentation, fossils and folding is evidence for changes in the Earth.
  1. Continents would we worn down by erosion if not for continuous mountain formation
  2. Erosion and sedimentation take place very slowly. Over periods of time these small changes add up to great changes in the Earhs surface
    1. Erosion makes new soil (essential for humans). Heating inside the earth changes rocks and lifts land
2. Earth's oldest rocks were made around 4.4 billion years old. Earth must be = or + this age
3. Wegeners Continental drift
  1. Proposed the theory was that the Earth's continents were once joined together, but gradually moved apart over millions of years.
    1. Geometric fit of continents
    2. matching rock formations and mountain chains
    3. Identical reptile fossil
  2. Rejection
    1. Simpler explanations using same evidence
      1. movements of continents not detectable
      2. too big of an idea with limited evidence
      3. Cooling earth caused mountains
        Wegener was an outsider to the geology community
        Land Bridge
4. Seafloor Spreading
  1. Convection currents in the mantle caused by the heating of the Earth's core pulls the ridge apart. Hot magma erupts and cools to make new rock.
    1. the seafloor spreads a few centimetres each year
    2. seafloor spreading and the periodic reversals of the Earth’s magnetic field can explain the pattern in the magnetisation of seafloor rocks on either side of oceanic ridges.
  2. Plate tectonics
    1. Earthquakes
      1. Earthquakes produce wave motions on the surface and inside the Earth which can be detected by instruments located on the Earth’s surface
        S-waves (Transverse)- SOLIDS ONLY
        In transverse waves, the vibrations are at right angles to the direction of travel and energy transfer.
        P- Waves (Longitudinal)- SOLIDS AND LIQUIDS
        In longitudinal waves, the vibrates are along the same direction as the direction of travel and energy transfer.
      2. Transform plate boundary. The friction at fault lines builds up to the point when the locked rocks break and the earth moves
    2. Mountains- collisions between plates
      1. Himalayas- the edges of plates crumple and pile up together
      2. When one plate is subducted under another, mountains are formed. The friction of the movement can also melt rocks and produce volcanoes.
    3. Volcanoes
      1. Formed at oceanic ridges
5. Inside the Earth
  1. Scientists began to notice that both P-waves and S-waves reached seisometers close to the epicentre
    1. Only P-waves reached seismometers on the other side of the Earth
      1. There were 'shadow zones' where S-waves didnt reach
        Scientists knew that the core must be liquid if S-waves couldn't pass through. From the size of the shadow zone, he worked out it was around 7000km thick
        Scientists looked at P-wave patterns and discovered there must be a small liquid core
Waves
1. distance = wave speed × time
  1. (metres, m) (metres per second, m/s) (seconds, s)
    1. a wave is a disturbance, caused by a vibrating source, that transfers energy in the direction that the wave travels, without transferring matter
      1. the frequency of waves, in hertz (Hz), is the number of waves each second that are made by the source, or that pass through any particular point
        the wavelength of waves is the distance between the corresponding points on two adjacent cycles
        the amplitude of a wave is the distance from the maximum displacement to the undisturbed position
2. wave speed = frequency × wavelength
  1. (metres per second, m/s) (hertz, Hz) (metres, m)
    1. for a constant wave speed the wavelength of the wave is inversely proportional to the frequency.

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OCR 21st Century P1

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