Orbits and the Wider Universe

• Kepler's First Law

  Planets move in an elliptical orbit with the Sun as one of its focus points
• Kepler's Second Law

  The planet will move faster when closer to the star and there will be equal areas covered in equal amounts of time
• Kepler's Third Law

  The square of the planet's orbital period is proportional to the cube of the semi major axis
• Evidence for Dark Matter

  • The measured orbital speeds at great distances from the centre of galaxies are much higher than predicted
  • This means that the mass much be much higher in these areas than observed
  • This suggests the existence of dark matter
  • (can be linked to orbital speed equation)
• The Higgs Boson is a very large subatomic particle that decays very quickly into all other forms of matter and could be the mechanism that creates dark matter
• Binary stars are two stars that orbit a common centre of mass with the same orbital speed
• Radial Velocity is the rate of change of distance between two points
• Recessional velocity is the rate at which an object will become more distant from the observer as a result of the expansion of the universe
• Hubble's Constant is the rate of the expansion of the universe
• Critical Density

  The average density of matter required for the universe to stop expanding, but only after an infinite amount of time