♡ Topic 7_Astronomy ♡

• The size of the star determines the type of lifecycle a star undergoes
• All stars of the same or greater size than the sun undergo the Protostar phase and Main sequence phase
• Stars like the sun become black dwarfs at the end of their life-cycle
• Stars much bigger than the sun can become neutron stars or black holes at the end of their lifecycle
• Stars of similar size to the sun go through the Red giant and White dwarf phases between being a main sequence star and a black dwarf
• Stars of greater size than the sun go through the Red supergiant and Supernova phases between being a main sequence star and a neutron star/black hole
• Transition of the star from the nebula stage to the main sequence:

  • The nebula increases in size until it is pulled in due to its gravity, causing GPE to turn into KE
  • Collisions between particles cause kinetic energy to turn into thermal energy
  • Eventually, the nebula becomes dense and hot enough to begin fusion
• When a star is a main sequence star:

  • Fusion in the star releases energy
  • Energy balances out with gravitational potential energy leaving the star
  • The star is in equilibrium and stable, not collapsing due to gravity or expanding due to radioactive behavior
• Transition to the red giant stage:

  • Once all hydrogen fuel is used up, the star fuses helium and other larger nuclei
  • This causes the star to expand and become a red giant
• Red giant becomes a white dwarf by:

  • Once all reactions have taken place, the star’s gravity pulls in all of its mass, making a small, dense white dwarf
  • The white dwarf will cool down to form a black dwarf
• Telescopes are located outside the earth's atmosphere because:

  • The earth's atmosphere absorbs many electromagnetic waves, making it difficult to detect certain waves
  • Light pollution can make some images less clear
  • Telescopes in space can operate both night and day
• Disadvantage of telescopes located outside the earth's atmosphere:

  • They are difficult to maintain as they have to be repaired in space (or brought down, which is unreasonably expensive)
• Disadvantages of optical telescopes:

  • Can only be used at night when the sky is clear
  • Can’t be used when the weather is cloudy
• Use of radio telescopes:

  • Not weather dependent, can be used in the rain as radio waves are not blocked by clouds
  • Usually large and expensive
• Steady State theory:

  • The universe has always existed
  • It is expanding and creating matter to counteract the loss in density
• Big Bang theory:

  • The universe expanded from a very small dense point about 14 billion years ago
• Red-shift:

  • A perceived increase in the wavelength of light due to the source moving away from the observer
• Red-shift provides evidence for:

  • The universe is expanding
  • This supports the Big Bang theory
• Big Bang theory suggests:

  • The entire universe started from a very small, hot and dense region in space
• Comparison of observed red-shift of two galaxies:

  • The galaxy further away is travelling faster
  • The observed red-shift is greater the further away it is
• Evidence for the universe expanding at an ever faster rate:

  • Observations of supernovae suggested galaxies are moving away at an ever faster rate
• Prior to observations of supernovae, belief about the rate of expansion of the universe:

  • The rate of expansion was expected to occur more slowly
  • It was thought that gravitational forces would cause this slowing down
• CMBR:

  • Cosmic Microwave Background Radiation
• CMBR provides further evidence for:

  • The Big Bang Theory
  • It is believed that CMBR originates from radiation produced in the Big Bang
• Existence of CMBR supporting the expansion of the universe:

  • Gamma radiation released in the Big Bang is thought to have been stretched by the expansion of the universe, resulting in the microwave radiation present today
• Why does your weight vary across planets?

  • Weight is dependent on g, as weight = mass x g
  • Gravitational field strength (g) of a planet varies depending on the size of the planet
  • This variation in g leads to weight differences across planets
• What is gravitational field strength on Earth?

  • Approximately 10 N/kg
• What does our solar system consist of?

  • The sun (our star)
  • 8 Planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune)
  • The planet’s natural satellites (e.g., the moon)
  • Dwarf planets
  • Comets and asteroids
• Name the planets in order, starting with the closest to the sun.

  Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and 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 and the planets orbit it
• What did Galileo contribute to theories about the universe?

  • Used telescopes to support Copernicus’ suggestions
  • Suggested that moons orbit planets
• Describe the orbits of moons, planets, comets, and artificial satellites.

  They orbit in an elliptical shape
• Explain why for a stable orbit, the radius of orbit must change if the speed changes.

  • Higher speeds require a greater centripetal force
  • Greater centripetal force needs an increase in gravitational force
  • Achieved by reducing the radius of the orbit
• Explain how the force of gravity acting on a satellite affects its speed and velocity.

  • The force can alter its velocity as the direction changes
  • It cannot change the speed as there is no force component in the direction of motion