Astrophysics

• What is the universe composed of?

  A large collection of billions of galaxies
• What is a galaxy?

  A large collection of billions of stars
• What is a solar system?

  A collection of planets orbiting a common star
• In which galaxy is our solar system located?

  Milky Way galaxy
• What does gravitational field strength measure?


  The force per unit mass on a body in a gravitational field
• In what units is gravitational field strength measured?

  Newtons per kilogram (N/kg)
• How does gravitational field strength vary?

  It varies with the mass and size of the body
• What is the formula for gravitational weight?


  $w =$$mg$
• What enables various bodies to orbit around others?

  Gravitational force
• What type of orbits do moons have?

  Moons orbit planets in slightly elliptical orbits with near constant orbital speed
• How do planets and comets orbit the Sun?

  Planets have slightly elliptical orbits with near constant orbital speed, while comets have highly elliptical orbits
• What is the relationship between orbital radius, time period, and orbital speed?

  The greater the orbital radius or the smaller the time period, the greater the orbital speed
• What is the formula for orbital speed?

  $v =$$\frac{2\pi r}{T}$
• Why do comets have greater speed when nearer to the star?

  Because the ice inside them melts as they get closer, causing their mass to decrease
• What is a nebula?


  A cloud of dust and gas where a star begins its formation
• What happens to particles in a nebula?

  They experience a weak attraction towards each other due to gravity and begin to clump together
• What occurs when pressure and temperature in a star are great enough?

  Nuclear fusion occurs
• What is produced during nuclear fusion in stars?

  Hydrogen nuclei fuse to form helium nuclei, releasing a large amount of energy
• What happens to the outward pressure in a star when hydrogen is used up?

  There is no longer enough outward pressure from nuclear fusion, causing the star to collapse
• What happens to a star similar in mass to the Sun after it collapses?

  It expands massively and becomes a red giant, then a white dwarf, and finally cools into a black dwarf
• What happens to a star with a mass larger than the Sun after it collapses?

  It expands and becomes a red super giant, then explodes in a supernova, leaving either a neutron star or a black hole
• How are stars classified?

  According to their colour, which is related to their surface temperature
• What is the relationship between a star's colour and its surface temperature?

  Hotter stars are bluer and cooler stars are redder
• What does the brightness of a star depend on?

  Where it is measured, represented using absolute or apparent magnitude
• What is absolute magnitude?

  The apparent magnitude a star would have if viewed from exactly 10 parsecs away
• What is apparent magnitude?

  How bright a star appears at a particular point in space
• What does a Hertzsprung-Russell diagram (HR diagram) show?

  • The relationship between a star’s surface temperature and brightness
  • Main components:
  • Supergiants (top right)
  • Red giants (below supergiants)
  • The Main Sequence (diagonal strip from top left to bottom right)
  • White dwarfs (bottom left)
  • Other stages are not shown as they are brief

  
• What does the Big Bang theory state?

  The universe expanded outwards from a single point
• What evidence supports the Big Bang theory?

  Red shift and cosmic microwave background radiation (CMBR)
• What does red shift indicate?

  That galaxies are moving away from us, with those furthest away moving the fastest
• What is cosmic microwave background radiation (CMBR)?

  Radiation released just after the Big Bang that has been stretched to become microwaves
• Why is the Big Bang theory the most accepted model?


  It accounts for all the experimental evidence
• What happens to the observed frequency and wavelength if a wave source is moving relative to an observer?

  There will be a change in the observed frequency and wavelength due to the Doppler effect
• What is an example of the Doppler effect?

  The siren of an ambulance is high-pitched as it approaches and low-pitched as it goes away
• What is the formula for the change in wavelength due to the Doppler effect?


  $\Delta \lambda =$$\frac{v}{c} \lambda_0$
• What does the red-shift of light from galaxies indicate?

  It indicates that the wavelength of the light is increasing as the galaxies move away from Earth
• How does the speed of a galaxy affect its red-shift?

  The faster it is moving, the more its light is red-shifted