Astrophysics

• Universe

  Galaxy

  Solar system

  Gravitational field strength

  Universe - large collection of galaxies

  Galaxy -large collection of stars

  Solar system - collection of planets orbiting a star

  Gravitational field strength - Force per unit mass - (N/kg)
• Orbits

  Moons

  Planets

  Comets

  Artificial satellites

  Orbital speed

  Moons - Slightly elliptical with near constant speed

  Planets -Slightly elliptical with near constant speed

  Comets - Highly elliptical , speed up when closer to star as ice melts decreasing mass

  Artificial satellites - orbit earth

  Orbital speed is increased by increasing orbital radius or decreasing time period
• Nebula-> Protostar

  1. Nebula -Cloud of dust and Gas pulled together due to gravitational forcesClouds of gas contract potential energy converted into kinetic energyMass drawn to centre of nebula gravity increases
  2. Protostar- Star forms when protostar becomes hot and pressure is great enough for fusion to occur.
• Fusion

  • Fusion - Hydrogen atoms fuse to make helium and release high amount of energy that release an outwards pressureHigh pressure causes particles to be more tightly packed ad more likely to collide with each otherHigh temperature means particles move faster and store more energy to overcome electrostatic force of repulsion
• Main sequence

  Main sequence - Star becomes stable as inward gravitational forces and outward pressure become balanced
• Red giant / Red Super giant

  Eventually hydrogen in the star is used up no more outward pressure from fusion so star collapses in on itself
• Red giants

  • If similar mass to the sun star expands and helium fuses to form heavier elements like carbon and nitrogen
• Red Super giant

  If mass is much greater than our sun expands to become super red giant and then explodes into a supernova where heaviest elements are fused up to iron then neutron star and black hole if massive
• What does the colour of a star depend on ?

  The colour of a star depends on the visible light it emits which depends on its surface temperature
• Colour order?

  The hotter the star...

  Hottest to coldest - Blue White Yellow Orange Red (lowest frequency of light is red)

  The hotter the star the more light of higher frequencies it will emit
• Finding Brightness using absolute magnitude

  Brightness depends on a stars size and temperature

  The bigger and hotter the brighter

  It depends on the stars distance from so we use absolute magnitude which allows us to compare brightness if it were 10 parsecs
• Hertz Sprung Russel Diagram

  What does it show?

  Other stages don't show because a star is only in them for a very short period of time

  It shows the relationship between a stars surface temperature and brightness

  or absolute magnitude against temperature
• Big Ban theory - what is it

  The Big Bang Theory states that the universe expanded outwards from a single point
• • Redshift The doppler effect

  As the wave source is moving away relative to an observer the wave will undergo an apparent change in frequency and wavelength when they are observed . If a light source is moving away it will appear to be shifted to the red end of the spectrum because the wavelength is being stretched.

  The further it is from earth the faster it is moving away and the more it is redshifted
• Cosmic microwave background radiation -

  After the Big bang lots of short wavelength radiation would have been emitted

  The radiation would have become stretched over time as the universe expands

  The fact CMBR is present everywhere you point a telescope
• Equation for calculating

  Change in wavelength over Reference wavelength = Velocity of a galaxy over speed of light