Topic 7 - Astronomy

• Why does your weight vary across planets?

  ● Your weight is dependant on g, since weight = mass x g

  ● The gravitational field strength (g) of a planet varies depending on the size of the planet

  ● This means that your weight will also vary
• What is the gravitational field strength on earth?

  10N/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 (ie. 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, 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?


  He used telescopes to support Copernicus' suggestions about the sun, and 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.


  ● At higher speeds, the object requires a greater centripetal force

  ● For a greater centripetal force, the gravitational force must increase

  ● This is achieved by the radius of the orbit being reduced
• Explain how the force of gravity acting on a satellite affects its speed and velocity

  ● The force can alter its velocity since the direction is continually changing

  ● It can't cause a change of speed since there is no force component in the direction of motion
• Describe the Steady State theory

  The Steady State theory says that the universe has always existed but is expanding and creating matter to counteract the loss in density.
• Describe the Big Bang theory

  The Big Bang theory states that the universe expanded from a very small dense point about 14 billion years ago.
• What is red-shift?

  When light rays moving away from us appear red, as the wavelength becomes stretched
• What does red-shift provide evidence for

  that the universe is expanding and supports the 'Big-Bang' theory
• What does the Big Bang theory suggest?

  The entire universe started from a very small, hot and dense region in space.
• Compare the observed red-shift of two galaxies, one further away than the other.

  ● The galaxy that is further away is travelling faster

  ● The observed red-shift is greater the further away it is
• What did scientists observe to provide evidence that the universe is expanding at an even faster rate?

  they observed supernovae, which suggested that galaxies are moving away at an even faster rate
• Prior to observations of supernovae, what was believed about the rate of expansion of the universe and why?

  ● The rate of expansion was expected to occur at an ever slower rate

  ● It was thought that gravitational forces would cause this slowing down
• What does CMBR stand for?

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

  ● The Big Bang Theory

  ● It is believed that CMBR originates from radiation produced in the big bang
• How does the existence of the CMBR support the expansion of the universe?

  - It is thought that gamma radiation was released in the Big Bang

  - The expansion of the universe has stretched this radiation, resulting in the microwave radiation present today
• 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?

  1. Protostar phase

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

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

  1. Neutron star

  2. 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?

  1. Red giant

  2. 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?

  1. Red super giant

  2. Supernova
• Describe the 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

  
  

  The collisions between particles cause this kinetic energy to turn into thermal energy

  
  

  Eventually the nebula will become dense and hot enough to begin fusion
• What occurs in the stage when a star is a main sequence star?

  - The fusion in the star releases energy

  - During fusion, main sequence stars mostly turn hydrogen into helium

  - thermal energy released from fusion causes an outward pressure which balances the inward pressure caused by gravity

  - the star is in equilibrium so will not collapse due to gravity or expand due to fusion. It is stable
• What happens when a star transitions to the red giant stage?

  Once all of the hydrogen fuel has been used up, the star begins to fuse helium and other larger nuclei

  
  

  This causes the star to expand and become a red giant
• How does a red giant become a white dwarf?

  ● Once all reactions have taken place, the star's gravity pulls in all of its mass, making a small, dense white dwarf

  ● This will cool down to form a black dwarf
• Why are telescopes located outside the earth's atmosphere?

  - the earths atmosphere absorbs many electromagnetic waves, making it difficult to detect certain waves

  - light pollution can make some images less clear

  - telescopes in space van operate both night and day
• What is the disadvantage of telescopes located outside the atmosphere?

  They are difficult to maintain as they have to be repaired in space (or brought down, which is unreasonably expensive).
• What are the disadvantages of optical telescopes?

  - They can only be used at night when the sky is clear

  - They can't be used when the weather is cloudy etc.
• Evaluate the use of radio telescopes.

  ● They are not weather dependent for example radio waves are not blocked by clouds so can be used in the rain

  ● They are usually large and expensive