8 - Space Physics

• What is a mnemonic to remember the order of the planets in the solar system?

  My - Mercury

  Very - Venus

  Enthusiastic - Earth

  Mother - Mars

  Just - Jupiter

  Served - Saturn

  Us - Uranus

  Nine - Neptune

  Pizzas - Pluto
• What is within our solar system?

  one star (the Sun), eight planets, the dwarf planets (including Pluto), and natural satellites (moons that orbit planets)
• What is our solar system a small part of?

  The Milky Way Galaxy
• How do stars form?

  - stars form from a cloud of dust and gas (nebula)

  - gravity causes the cloud of gas and dust to collapse (collapsing cloud of hot gas and dust is a 'protostar') => as the dust particles move faster, temperature rises to millions of degrees celsius

  
  

  - if the temperature of the protostar gets high enough, then hydrogen nuclei join together to form helium (process is called nuclear fusion) => protostar => star
• What does nuclear fusion release?


  a huge amount of energy
• What happens a star that is undergoing nuclear fusion?

  There are two opposing forces acting within the star:

  
  

  - force of gravity acts inwards => causes the star to collapse

  
  

  - energy from nuclear fusion creates a force acting outwards => causes the star to expand
• What forces are balanced?

  - the force of gravity acting inwards is balanced by the force due to fusion energy acting outwards

  
  

  => star is in equilibrium
• What is a star's life cycle determined by?

  the size of the star
• What happens in a main-sequence star when the hydrogen begins to run out?

  - the outward force due to fusion energy is less than the inward force due to gravity => star collapses inwards => temperature increases =>

  helium nuclei fuse together to create heavier elements => star expands to form a red giant
• What happens when a red giant stops fusing helium?

  - star shrinks and forms a whte dwarf (no longer carrying out fusion so it gradually cools down)
• What is formed when a white dwarf eventually stops releasing any energy?

  - when the white dwarf stops releasing any energy, a black dwarf is formed
• What happens when a star, that is much bigger than our Sun, runs out out hydrogen?

  - they leave the main-sequence stage and expand into red super giants
• What is similar with smaller stars like the Sun and the red super giants?

  - helium nuclei fuse together to produce heavier elements
• What is the heaviest element that nuclear fusion can make with a star that is the same size as the Sun?

  - nuclear fusion cannot make elements heavier than iron
• What happens when red super giants stop carrying out nuclear fusion?

  - the star explodes => supernova
• How can supernovas create elements heavier than iron?


  - temperature of a supernova is high enough to produce elements heavier than iron (when the supernova explodes, these elements are distrubed throughout the Universe)
• What 2 objects can form after a supernova?

  - neutron star

  - black hole
• What does a neutron star consist of?

  - neutrons densely packed together
• What is special about a black hole?


  - a black hole has such a large gravity that not even light can escape
• What is it called when the Earth rotates around the Sun?


  - a circular orbit as the Earth follows the path of a circle around the Sun
• What is the more realistic orbit called?

  - elliptical orbit

  
• How do planets and satellites maintain their circular orbits?

  - gravity provides the force (e.g. the force of gravity acting between the Sun and the Earth holds the Earth in its orbit)
• Give an example of a natural satellite?

  - the Moon is a natural satellite
• Give an example of an artifical satellite?

  - the International Space Station
• What is the difference between artifical satellites and natural satellites?

  - artificial satellites are man-made that can be used to study the Earth, other planets, to help us communicate, and even to observe the distant Universe
• What are geostationary satellites?

  
  

  What does this mean about their position to the Earth?

  - geostationary satellites orbit once every 24hours

  
  

  - as the Earth takes 24hours for one full spin, the geostationary satellites always point to the same part of the Earth
• Why does the force of gravity acting on satellites lead to a change in velocity but not a change in speed?

  - velocity is a vector quantity (involves magnitude AND DIRECTION) so the direction is always changing but the speed remains constant
• What happens to the radius of a satellite's orbit is the speed increases?

  
  

  Why does this happen?

  
  

  What does this relationship lead to?

  - if a satellite orbits at an increased speed, then the radius of the satellite's orbit decreases

  
  

  - at a greater speed, the satellite needs a greater force of gravity to prevent it flying off into space (satellite comes closer to the Earth)

  
  

  => stable orbit
• In the 1900s, what did astronomers detect about the light from distant galaxies?

  - they detected that the light from very distant galaxies had an increased wavelength compares to light from closer galaxies
• On a spectrum, how can we identify absorbed wavelengths?


  - certain elements absorb light of specific wavelengths => those specific wavelengths appear as dark, vertical lines

  
• On a spectrum of light from a distant galaxy, what will we notice about the absorbed wavelengths of light?

  
  

  What do scientists call this effect?


  - all the lines will have shifted slightly towards the red end of the spectrum

  
  

  (red-shift)
• What does the red-shift tell us?

  - galaxies are moving away from each other (observed wavelength is increased)
• How can we identify fast-moving galaxies?

  - galaxies that are further away have a bigger red-shift so these galaxies are moving faster than galaxies that are closer
• What does red-shift provide evidence for?


  - the fact that distant galaxies are moving faster than nearby galaxies provides evidence tat hee universe is expanding (supports The Big Bang theory)
• What do scientists believe about The Big Bang theory?

  - scientists believe that the universe began from a very small region that was extremely hot and dense...which expanded into the universe we see today
• What did observations of supernovae sugest?

  - scientists used to think that due to gravity, the expansion of the Universe would slow down

  - observations of supernovae suggest that distant galaxies are actually receding increasingly faster
• Give 2 examples of what is still not understood about the Universe.

  - dark mass/matter

  - dark energy