space physics

• heliocentric


  lies at the centre of our solar system (our sun)
• smaller planets are made of primarily rock, then the larger planets are primarily gas.
• all planets rotate, just at different speeds. some planets rotate in the opposite direction or on a skewed axis to the other planets, and this may be due to past collisions throwing its axis off balance.
• larger planets have rings, as their gravitational field is so strong it attracts debris.
• order of the planets in the milky way:

  mercury, venus, earth, mars, jupiter, saturn, uranus, neptune, (pluto)
• the first solar system model was...

  • geocentric model
  • the earth was at the centre and everything orbited it in perfect circles
  • fixed background of stars
• 600 years after the geocentric model, the heliocentric model was formed, with the sun at the centre.

  • the main evidence being mars' 'retrograde motion' (earth orbits the sun faster than mars, so we undertake it, so it appears to reverse its direction in the sky
  • galileo observing moons orbiting jupiter showed not everything orbited the earth
  • kepler showed that the planets orbited in ellipses, and not circles.
• as the planet orbits the sun, the gravitational force causes the planet to change direction constantly (it moves in a circle around the sun) this means that the velocity is always changing, hence the force causes the planet to accelerate without increasing its speed.
• what is needed for a stable orbit

  if the planet moves closer to the sun (its orbital radius decreases), the gravitational attraction to the sun increases (force increases and so does acceleration), so the orbital speed of the plant increases.
• if the planet moves further away from the sun (orbital radius increases), then the gravitational attraction to the sun decreases (so does force and acceleration). The orbital speed of the planet decreases.
• nebula


  all stars form from a giant cloud of hydrogen gas and dust called a nebula
• formation of a protostar

  the force of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas known as a protostar. as the particles are pulled closer together, the density of the protostar will increase, resulting in more frequent collisions between the particles which causes the temperature to increase.
• formation of a main sequence star

  once the protostar becomes hot enough, nuclear fusion reactions occur within its core. the hydrogen nuclei will fuse to form helium nuclei. every fusion reaction releases heat (and light) energy which keeps the core hot.
• once a star is born, it is known as a main sequence star. during the main sequence, the star is in equilibrium and is said to be stable - the inward force due to gravity is equal to the outward pressure force from the fusion recations.
• if the main sequence star is about the same size as the sun (a small star) it will then form a red giant star -> planetary nebula -> white dwarf -> black dwarf.
• if the main sequence star is much bigger than the sun (big star) it will form a red super giant star -> supernova -> (if big star) neutron star -> (if really big star) black hole.
• formation of a planetary nebula (small star)

  once the second stage of fusion reactions have finished, the star will become unstable and eject the outer layer of dust and gas. the layer of dust and gas which is ejected is called a planetary nebula
• white dwarf formation (small star)

  the core which is left behind from a planetary nebula will collapse completely due to the pull of gravity the star will become a white dwarf. the white dwarf will be cooling down and as a result, the amount of energy it emits will decrease
• black dwarf formation (small star)

  once the white dwarf has lost a significant amount of energy it becomes a black dwarf. it will continue to cool until it eventually disappears from sight
• formation of a red giant (small stars) and red super giant (big stars)

  eventually, the star runs out of gas to fuse. this means it is no longer in equilibrium, so it collapses. this causes the core to shrink and heat up as the inward force due to gravity will become greater than the outward force of pressure. a new series of reactions then occur around the core, for example, helium nuclei will undergo fusion to from beryllium. these reactions cause the outer part of the star to expand and become red from the outer surface starting to cool
• formation of a supernova (larger stars)

  once the fusion reactions inside the red supergiant finally finish, the core of the star will collapse suddenly causing a gigantic explosions called a supernova. at the centre of this explosion, a dense body called a neutron star will form. the outer remains of the star will be ejected into space during the supernova explosion, forming a planetary nebula
• formation of a neutron star or black hole depending on the size of the star (larger stars)

  in the case of the biggest stars, the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole. (an extremely dense point in space that not even light can escape from)
• supernovas

  a supernova is a bright and powerful explosion that happens at the end of a massive star's life. the explosion releases a large amount of energy. during a supernova, all of the elements which were produced by the fusion reactions are exploded out along with neutrons. the neutrons combine with the elements to form even heavier elements these elements are ejected into the universe by the supernova explosions and form new planets and stars
• since the earth contains many heavier elements up to iron, this is proof that it must have once been made from the remains of as supernova
• light appears red shifted from galaxies which are moving away from earth. the change in the distance of each galaxy's speed is evidence of an expanding universe. as wavelength appears to get larger (more visible in the red end of the visible spectrum) frequency appears to decrease, as each time a wavelength is emitted, the source (galaxy) is further away.
• evidence for the big bang

  red shift, CMB (cosmic microwave background radiation)
• there is so much about the universe that is not understood, for example, dark mass and dark energy
• CMB - cosmic microwave background radiation

  when the universe was very young, everything, the stars and rock, would be very hot and should have emitted lots of short-wavelength radiation. this radiation, as the universe expanded over time, would have been stretched to become microwaves. this background radiation is present wherever you point a telescope in the sky which proves that the hot young unniverse has cooled and expanded since.
• as the big bang accounts for all the experimental evidence, it is the most accepted model currently