Space physics

• Planets


  Large objects that orbit stars.

  They have a sufficient mass to assume hydrostatic equilibrium (a nearly round shape)

  It has a cleared orbit
• Stars


  Any massive self-luminous celestial body of gas that shines by radiation derived from its internal energy sources
• Natural satellite


  A body orbiting another planet or dwarf planet
• Satellite


  smaller planetary bodies that orbit around other planetary bodies. (artificial satellites are satellites humans have built)
• Doppler effect


  If an object that is emitting waves moves away from an observer, the observer will receive the wavefronts further apart.

  Hence the waves they receive have a larger wavelength than these emitted

  If an object that is emitting waves moves towards the observer, the observer will receive the wavefronts closer together

  Hence the waves they receive have a shorter wavelength
• Acceleration in orbits


  An object moving in a circle, is constantly changing direction hence it is changing velocity

  The acceleration is acting inwards towards the centre of the circle

  Therefore a force must be pulling towards the centre of the circle
• Direction and proximity of orbits

  The closer you get to a star or planet, the stronger the gravitational force is.

  The stronger the force, the faster the orbiting object needs to travel to remain in orbit (to not crash into the object that it is orbiting ).

  For an object in a stable orbit, if the speed of the object changes, the size/radius must do so too. Faster moving objects will move in a stable orbit with a smaller radius than smaller moving ones
• Red shift


  If visible light is emitted from a moving source , then an increase in wavelength will cause a shift to the red-end of the spectrum., this is known as red shift.

  The faster a star or galaxy is moving (relative to an observer) the bigger the shift is
• Evidence for the BIG BANG theory


  The discovery of CMBR (cosmic microwave background radiation) shows a high amount of radiation all around us in the universe

  The only way it could be there is from a large output of energy(the big bang)
• Hubble's observations

  • Light from distant galaxies is red-shifted
  • The further the galaxy, the greater the red-shift is
• Hubble's conclusions

  • Distant galaxies are moving away
  • The further away a galaxy is, the further it is moving away from earth
  • Therefore the whole universe is expanding
• red shift = away from us (long wavelength)

  blue shift = towards us (short wavelength)
• What will happen in the future

  Whether the universe will continue to expand forever, or one day collapse, it will depend on how much mass there is in it.

  If the universe has a lower density, it'll expand forever (big yawn) if it has a larger density it'll one day collapse (big crunch)
• LIFE CYCLE OF STARS (1):

  • Initially, there is a stellar nebula which is a cloud of dust and hydrogen gas out in space
  • Gravity pulls the dust and hydrogen together
  • This creates a protostar which is a very small star and fusion begins which gives off light.
  • As the force of fusion is greater than the force of gravity, there is a resultant force outwards and this creates a main sequence star, at this point, the fusion outwards is balanced by the gravity pulling inwards.
• LIFE CYCLE OF STARS (2):

  • If the main sequence star is lighter in mass, eventually the force of gravity is stronger than the force of fusion because the hydrogen runs out.
  • This allows the gas to compress and gets hotter therefore heavier element can fuse which allows the star to expand again, this creates a red giant
  • Eventually the fusion of Helium runs out so the force of gravity> fusion, which then creates a white dwarf.
  • White dwarves don't give out any heat so they cool down to the same as their surroundings and eventually forms a black dwarf.
• LIFE CYCLE OF STARS (3):

  • If the main sequence star is heavier in mass it becomes a red giant.
  • When it collapses and explodes it will become a supernova.
  • From this point if the supernova is lighter in mass it will become a neutron star that is made of neutrons, this is because the density and pressure are very high so it fuses protons and electrons to form neutrons.
  • If the supernova is heavier in mass, it is likely to become a black hole