Topic 7: Astronomy

• What is the formula for weight?

  Weight = mass x gravitational field strength
• Why does weight vary across planets?

  Weight depends on gravitational field strength (g)
• What is the gravitational field strength on Earth?

  Approximately 10 N/kg
• What are the components of our solar system?

  • The sun (our star)
  • 8 planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
  • Natural satellites (e.g., the moon)
  • Dwarf planets
  • Comets and asteroids
• Name the planets in order from the sun.

  Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
• What did Ptolemy suggest about the universe?


  That the Earth was at the centre
• What did Copernicus suggest about the universe?


  That the sun is at the centre
• What did Galileo contribute to theories about the universe?

  He used telescopes to support Copernicus' ideas
• Describe the orbits of moons, planets, comets, and artificial satellites.

  • They orbit in an elliptical shape.
• Why must the radius of orbit change if speed changes for a stable orbit?

  Higher speeds require greater centripetal force
• How does gravitational force affect a satellite's speed and velocity?

  It alters velocity but not speed
• Why does the direction of a satellite's motion change?

  Because the gravitational force continually changes direction
• What does the Steady State theory propose about the universe?

  The universe has always existed and is expanding
• How does the Steady State theory explain the creation of matter?

  It creates matter to counteract density loss
• What does the Big Bang theory state about the universe's origin?

  The universe expanded from a small dense point
• How long ago did the Big Bang occur?

  About 14 billion years ago
• What is red-shift?

  A perceived increase in light wavelength
• What does red-shift indicate about the movement of celestial objects?

  It indicates the source is moving away
• What evidence does red-shift provide for the universe?

  It supports that the universe is expanding
• How does red-shift support the Big Bang theory?


  It shows galaxies are moving away from us
• What does the Big Bang theory suggest about the universe's initial state?

  The universe started from a small, hot region
• How does the observed red-shift differ between two galaxies at varying distances?

  The further galaxy is traveling faster
• What did scientists observe to conclude the universe is expanding faster?

  They observed supernovae suggesting faster movement
• What was the prior belief about the universe's expansion rate before supernova observations?

  Expansion was expected to slow down
• Why was it thought that the universe's expansion would slow down?

  Gravitational forces were expected to slow it
• What does CMBR stand for?

  Cosmic Microwave Background Radiation
• What does CMBR provide evidence for?

  It supports the Big Bang Theory
• What is believed to be the origin of CMBR?

  Radiation produced in the Big Bang
• How does CMBR support the expansion of the universe?

  Gamma radiation was stretched during expansion
• What happens to gamma radiation as the universe expands?

  It stretches into microwave radiation
• What factor determines the type of lifecycle a star undergoes?

  The size of the star.
• Which two phases do all stars of the same or greater size than the sun undergo?

  Protostar phase and Main sequence phase.
• What do stars like the sun become at the end of their life-cycle?

  A black dwarf.
• What two things can stars much bigger than the sun become at the end of their lifecycle?

  Neutron star and Black hole.
• What two phases do stars of similar size to the sun go through between being a main sequence star and a black dwarf?

  Red giant and White dwarf.
• What two phases do stars of greater size than the sun go through between being a main sequence star and a neutron star/black hole?

  Red supergiant and Supernova.
• Describe the transition of the star from the nebula stage to the main sequence.

  • Nebula increases in size due to gravity.
  • Gravitational potential energy turns into kinetic energy.
  • Collisions cause kinetic energy to become thermal energy.
  • Nebula becomes dense and hot enough for fusion.
• What occurs in the stage when a star is a main sequence star?

  • Fusion releases energy.
  • Energy balances gravitational potential energy.
  • Star remains in equilibrium and stable.
• What happens when a star transitions to the red giant stage?

  • Hydrogen fuel is used up.
  • Star begins to fuse helium and larger nuclei.
  • Star expands and becomes a red giant.
• How does a red giant become a white dwarf?

  • Gravity pulls in all mass after reactions.
  • Forms a small, dense white dwarf.
  • White dwarf cools down to form a black dwarf.