Space

• Luminosity - the rate of light energy released or power output of a star
• Intensity - the power received from a star per unit area
• Parallax - the apparent change of position of a nearer star in comparison to distant stars
• Parsec - the distance when the parallax angle is 1 arcsecond
• Parallax method only works when the distance is less than 100 light years.
• Standard candle - an object with a known luminosity.

  Astronomical distances can be determined by measuring the intensity.
• Life cycle of a star

  • Nebula
  • Protostar
  • Main sequence

  Small

  • Red giant
  • White dwarf

  Big

  • Red supergiant
  • Supernova
  • Neutron star or black hole / singularity
• Protostar - dust and gas collect due to gravity
• Main sequence star

  • gravity and fusion are in equilibrium
  • hydrogen nuclei are fused into helium
• Red giant

  • hydrogen runs out
  • helium is fused into heavier elements
• White dwarf

  • fusion stops when the star runs out of fuel
  • gravity is greater than outwards force, so the star collapses
• Red supergiant

  • hydrogen runs out
  • helium is fused into heavier elements
• Supernova

  • fusion stops when the star runs out of fuel
  • core collapses inwards suddelny
  • elements heavier than iron are fused
• Neutron star

  • gravity forces protons and electrons into neutrons
• Main sequence star on HR diagram

  • begins as a protostar
  • heats up , moving left
  • becomes main sequence star
  • runs out of hydrogen, moves up and right
  • becomes red giant
  • runs out of helium, moves down and left
  • becomes white dwarf
• z = red shift

  lambda = original wavelength

  f = original frequency

  v = receding velocity
• Hubbles constant - rate of expansion of the universe
• Controversy over the age and fate of the universe

  • difficulty making accurate measurements of distances to galaxies
  • hubble’s constant has a large uncertainty
  • existence of dark matter
  • dark energy may mean we don’t understand gravity as we think