Space-Physics

• Within our solar system there is one star, the Sun, plus the eight planets and the dwarf planets that orbit around the Sun
• Natural satellites, such as moons that orbit planets, are also part of the solar system
• The sun lies at the centre of our solar system, making it heliocentric
• Dwarf planets, including Pluto and Ceres, also orbit the sun
• Asteroids and comets are also part of our solar system
• Our solar system is a small part of the Milky Way galaxy
• The planets in our solar system are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, (Pluto)

  • A mnemonic to remember the order of the planets is: My Very Early Morning Jam Sandwich Usually Nauseates (people)
• Smaller planets are primarily made of rock, while larger planets are primarily made of gas
• All planets orbit the Sun on the same plane
• All planets rotate, but at different speeds

  • Some planets rotate in the opposite direction or on a skewed axis due to past collisions throwing their axis off balance
• Larger planets have rings due to their strong gravitational field attracting debris
• Initially, the geocentric model placed Earth at the centre of the solar system with everything orbiting in perfect circles
• 600 years later, the heliocentric model was formed with the sun at the centre

  • Evidence for this model includes Mars' retrograde motion and Galileo observing moons orbiting Jupiter
• Kepler showed that planets orbit in ellipses, not circles
• As a planet orbits the sun, the gravitational force causes the planet to constantly change direction, leading to changing velocity

  • This force causes the planet to accelerate without increasing its speed
• For a stable orbit:

  • If a planet moves closer to the sun, its gravitational attraction increases, leading to an increase in orbital speed
• In the life cycle of a star:

  • Dust and gas clouds in a galaxy are drawn together by gravitational attraction
  • The cloud becomes more concentrated as particles get closer, increasing temperature and pressure
  • Fusion occurs as light nuclei fuse together to form helium nuclei, releasing energy that opposes gravitational collapse
  • Eventually, the star runs out of gas to fuse, leading to collapse
  • If massive, the star produces a supernova and may become a neutron star or black hole
  • If normal-sized, the star produces a planetary nebula and a white dwarf remains
• Red Shift:

  • Light appears red-shifted from galaxies moving away from Earth
  • The change in each galaxy's speed with distance is evidence of an expanding universe
  • Red Shift supports the Big Bang theory, showing the universe is expanding from a single point
• Evidence for the Big Bang includes:

  • Red Shift showing the expanding universe
  • Cosmic Microwave Background radiation, which proves the cooling and expansion of the universe over time
• The Big Bang theory is the most accepted model currently, explaining experimental evidence
• The life cycle of a star begins with a dust and gas cloud present in a galaxy
• Gravitational attraction between the gas/dust particles draws them together, causing the cloud to become more concentrated
• As particles get closer, the temperature and pressure of the cloud increases
• When the pressure gets great enough, gas/dust particles fuse together through fusion, mainly hydrogen gas nuclei fusing to form helium nuclei
• Fusion releases a large amount of energy, opposing the collapsing of the cloud due to gravity
• An equilibrium forms where the energy released from fusion balances the pressure of gravitational collapse, resulting in the formation of a star that will stay like this for billions of years
• Eventually, the star runs out of gas to fuse, leading to a collapse if massive or normal-sized
• If Massive:

  • The star collapses, increasing the pressure and temperature of the core, allowing heavier elements to fuse. Once all fusion occurs, the star is too massive to be stable, leading to a supernova
  • What remains is either a neutron star or black hole
• If Normal-sized:

  • The star collapses, producing a planetary nebula with less fusion occurring due to less fuel to fuse
  • A white dwarf remains after the collapse
• Artificial Satellites: Man-made satellites sent into space for satellite imaging and communications
• Big Bang Theory: The currently accepted model for the origin of the universe
• Circular Orbits: Planets and satellites travel in circular orbits due to gravity
• Dark Energy: A hypothesised form of energy responsible for the universe's increasing rate of expansion
• Dark Mass: A hypothesised type of mass used to explain galaxies rotating faster than expected for their observed mass
• Main Sequence Star: The stable state of all stars where gravitational forces and pressure are balanced
• Milky Way Galaxy: The galaxy where our solar system is located
• Natural Satellites: Moons that orbit planets
• Nebula: A cloud of dust and gas
• Protostar: The first stage all stars go through after forming from a nebula
• Red Giant Star: Stars similar to the Sun that expand to form a red giant when hydrogen is used up