topic 7 astronomy

• What is a nebula?

  Cloud of dust and gas
• What happens during the formation of a protostar?

  Gravity pulls dust and gas together, raising temperature
• What initiates nuclear fusion in a protostar?

  High temperature allows hydrogen nuclei to fuse
• What is a main sequence star?

  Long stable period of a star
• What balances the force of gravity in a main sequence star?

  Outward pressure from thermal expansion
• How does the mass of a star affect its time on the main sequence?

  Heavier stars have shorter main sequence lifetimes
• What occurs when hydrogen runs out in a star?

  Gravity overcomes thermal expansion, causing compression
• What is a red giant?

  Star that expands and cools after hydrogen depletion
• What is a white dwarf?

  Hot, dense, solid core after outer layers are ejected
• What happens during a supernova?

  Star glows brightly and eventually explodes
• What is left after a supernova explosion?

  Dense core called neutron star or black hole
• What is CMB radiation?

  Leftover energy from the initial explosion
• What does red shift indicate?

  Increase in wavelength from objects moving away
• How does CMB radiation support the Big Bang model?

  It shows the Universe had a beginning
• What is the Steady State Theory?

  Universe has always existed, with constant matter creation
• What is the Big Bang theory?

  All matter was once in a small, dense space
• What does the geocentric model suggest?

  Earth is at the center of the universe
• What does the heliocentric model propose?

  Sun is at the center of the Solar System
• What does the force of gravity depend on?

  Mass and distance between objects
• How does distance affect gravitational force?

  Closer objects experience a stronger gravitational force
• What happens to the speed of an object in stable orbit if its radius changes?

  Speed must change if radius changes
• How do planets move around the Sun?

  In almost circular orbits
• What is true about an object in circular orbit at constant speed?

  It is constantly accelerating towards the center
• What is centripetal force?

  Force acting towards the center of a circle
• What are the stages in the life cycle of a star?

  1. Nebula
  2. Protostar
  3. Main Sequence star
  4. Red giant or red supergiant
  5. White dwarf or supernova
  6. Neutron star or black hole
• What are the differences between the Big Bang theory and Steady State theory?

  • Big Bang: Universe had a beginning, all matter in a small space, expanded after explosion
  • Steady State: Universe has always existed, new matter created as it expands, no beginning or end
• What are the key differences between the geocentric and heliocentric models?

  • Geocentric: Earth at center, celestial bodies orbit Earth
  • Heliocentric: Sun at center, planets orbit the Sun
• Astronomical objects found in the Solar System

  • star
  • planets
  • moons
  • comets
  • asteroids
• Shape of planet's orbit around the Sun

  circular orbit around the Sun
• Why is the star stable during main sequence

  Gravitational pull inwards

  Outwards force due to fusion reactions

  Both forces are in equilibrium
• What happens to the Sun between main sequence and the end of its life cycle?

  The Sun will expand to become a red giant

  • then the star will collapse to become a white dwarf
  • the star will cool to become a black dwarf
• Life cycle of a star

  1. Starts as a nebula
  2. Gravity brings the gas together to form a protostar
  3. Then it enters the main sequence (gravity balanced with outward force due to fusion)
  4. Star cools and expands and explodes in a supernova
  5. Leaves behind a very dense neutron star or a black hole
• Process of nuclear fusion in stars

  two small nuclei join together to produce a larger nucleus. This releases energy/gamma radiation
• Red shift and Big Bang Theory evidence

  If galaxies are now moving apart from one another they must have previously been closer together.

  This proves that they originated from a very dense region in space where the big bang occured
• CMBR evidence for Big Bang Theory

  CMBR appears the same in all directions

  • All parts of the universe were in contact a long time ago
  • wavelength has increased (universe has expanded)
• What causes the red shift of light from distant galaxies?

  the doppler effect due to the relative motion between the observer and the source
• Describe the methods scientists have used to help with this search in our Solar System

  • telescopes
  • search for evidence of conditions needed for life e.g. water/oxygen
  • manned missions
  • unmanned missions to other planets
  • landers/robots
• Describe the methods scientists have used to help with this search in rest of Universe

  • search for SETI
  • use radio telescopes
  • search for regular pattern of radio signals
  • discovery of other planetary systems
  • broadcasting signals
• State what is meant by red-shift

  the change in the observed frequency or wavelength of light received from a distant galaxy