PMT notes - space physics

• our star is called the sun
• the planets in the solar system go in the order Mercury Venus Earth Mars Jupiter Saturn Uranus
• the asteroid belt is in between Mars and Jupiter
• Jupiter has 16 moons
• Saturn has rings made out of rock and dust
• Pluto is a dwarf planet
• gravity between two planets depends on the mass of the planets and their seperation
• weight = mass x gravitational strength
• the seasons variate throughout the year from Earth being tilted on its axis
• daylight hours , temperature , suns height in sky at midday are all affected by the Earths axis
• Earth tilted towards the sun --> summer
• equinox --> 12 hours day and night
• lightyear is the distance travelled by light per year
• a nebula is a huge cloud of hydrogen gas and dust
• a protostar is when a nebula has collected into a sphere
• a main sequence star is a star that has started nuclear fusion
• a red giant is the size of the sun
• a red super giant is a high mass star
• a red giant turns into a white dwarf then a black dwarf
• a red supergiant explodes in a supernova explosion
• a supernova turns into a neutron star or a black hole
• the bigger a star is the hotter it's core , hydrogen turns to helium faster , heavier nucleii can be formed by fusion , less tume is spent as a main sequence star
• Solar Systems components


  One star (the Sun), plus the eight planets and the dwarf planets that orbit around the Sun, and natural satellites (moons) that orbit planets
• The sun lies at the centre of our solar system, it is heliocentric
• Planets in the solar system

  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
  • Uranus
  • Neptune
  • (Pluto)
• Smaller planets are made of primarily rock
• Geocentric model

  Initially, Earth was at the centre, the planets, our moon, and the sun, orbited the Earth
• Planetary Orbits

  1. Gravitational force causes the planet to change direction constantly (it moves in a circle around the sun)

  2. This means the velocity is always changing

  3. Hence the force causes the planet to accelerate without increasing its speed
• For a stable orbit


  If the planet moves closer to the sun (orbital radius decreases), the gravitational attraction to the sun increases, so the orbital speed of the planet increases
• Life Cycle of Star

  1. Dust and gas cloud is present in a galaxy

  2. The gravitational attraction between the gas/dust particles draws them together

  3. The cloud becomes more concentrated, as the particles get closer

  4. The temperature and pressure of the cloud increases as the particles get pushed so close together

  5. Eventually the pressure gets so great that the gas/dust particles are able to fuse together

  6. Fusion occurs as the light (mainly hydrogen gas) nuclei fuse together to form helium nuclei, creating a large amount of energy

  7. This release opposes the collapsing of the cloud due to gravity

  8. So eventually an equilibrium forms, where the energy released due to fusion balances the pressure of gravitational collapse

  9. Eventually the star runs out of gas to fuse, so it collapses

  10. If Massive, the star will collapse, increasing the pressure + temperature of the core, meaning heavier elements can fuse. Once all the fusion has happened, it is too massive to be stable, so the star collapses, rebounds on its centre and produces a supernova

  11. What remains is either a neutron star or black hole

  12. If Normal-sized, the same process happens, less fusion occurs however (less fuel to fuse), the star collapses, and produces a planetary nebula, a lower scale supernova, and a white dwarf remains
• Red Shift

  Light appears red shifted from galaxies which are moving away from Earth, evidence of an expanding universe
• As the universe expands, the distance from the galaxies also expands, so light from a galaxy has its wavelength "red-shifted" as it appears to move away from us, and the frequency appears to decrease
• Evidence for the Big Bang


  • Red Shift
  • CMB (Cosmic Microwave Background radiation)
• The Big Bang accounts for all the experimental evidence, so it is the most accepted model currently
• There is much about the universe that is not understood, for example dark mass and dark energy
• moons are a natural satellite
• the larger planets are made of primarily gas
• All of the planets in our solar system orbit the Sun
• All of the planets rotate but 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