PHYSICS (stars and planets)

• Solar System

  The planets keep in orbit by gravitational forces
• Inner rocky planets

  • Separated from outer gaseous planets by a band of rocky material (asteroid belt)
  • asteroid belt contains dwarf planets and asteroids
• Inner planets


  • Mars
  • Mercury
  • Earth
  • Venus
• Inner planets

  • Formed from denser material
  • Have solid surfaces
• Outer planets


  • Jupiter
  • Saturn
  • Uranus
  • Neptune
• Outer planets

  • Formed from gaseous materials from dust and gas cloud
  • Larger in size
  • Less dense
• Formation of the solar system

  1. Cloud of dust and gas rich in hydrogen contracted under gravity

  2. Cloud compressed making it hotter

  3. Cloud spun

  4. Protostar formed at the centre, this got hot enough for nuclear fusion to occur and made the sun

  5. Cloud spun around sun, getting thinner, so particles stuck together to make clumps (planets)

  6. Denser materials felt stronger gravitational pull so migrated closer to the sun

  7. Icy matters settled in outer solar system
• Solar system is roughly 4600 million years old
• Things in the solar system

  • Stars
  • Planets
  • Pluto-dwarf planet
  • Moons
  • Comets
  • Asteroids
• Moons

  Mass roughly < 10^23 kg, natural satellite
• Comets

  Large balls of rock and ice, near sun so melts and is vaporised seen as vapour tail, highly elliptical and regular orbit
• Asteroids

  Large rocks found in asteroid belt
• Galaxies

  Composed of hundreds of millions of solar systems, centre is supermassive black hole
• pluto

  dwarf planet,

  irregular elliptical orbit

  as distance from the sun increases its orbit becomes longer
• Hertzsprung-Russel (H-R) Diagrams

  Classify stars through comparing temperature and brightness (Luminosity)
• Stars on the H-R Diagram

  • Stars on the diagonal line of the diagram are on the main sequence
• Life cycle of the Sun

  1. Sun becomes red giant

  2. Sun becomes white dwarf
• Astronomical unit (AU)

  • Unit used to measure distances in space because the distance between planets is so great
  • 1 AU = 150,000,000 km = 1.5 x 10^11 m
  • The average distance from the Sun to the Earth. To get from km > AU it’s the planet distance divided by the earths distance
• Light year

  • The distance that light will travel in 1 year
  • 1 light year = 9.46 x 10^15 m
• Planets' distances are measured relative to the Earth's distance from the Sun
• lifecycle of a low mass star

  1. nebula
  2. protostar
  3. main sequence star
  4. red giant
  5. white dwarf
  6. planetary nebula
  7. red dwarf
  8. black dwarf
• lifecycle of a high mass star

  1. nebula
  2. protostar
  3. main sequence star
  4. super giant
  5. neutron star / black hole
• nebula

  cloud of dust and gas.

  all stars start out as a nebula and over millions of years gravity pulls these closer together overtime dust and gas particles clump together then attract more dust and gas through gravity.

  pressure builds up and the core starts to heat up due to friction this then forms a protostar.
• protostar

  as dust and gas from the nebula is added to the protostar it gains mass as mass is gained gravity increases and the temperature in the protostar increases the gravity eventually gets so large and the temperature gets so high that molecular fusion starts and it becomes the main sequence star
• molecular fusion

  2 atoms fuse together to form a molecule
• main sequence star

  Stars mainly use small elements, particularly hydrogen and helium to produce energy in a process called molecular fusion

  gravitational force due to the stars mass pushes inwards

  radiation pressure due to the stars using hydrogen as a fuel pushes out almost all stars spend the whole lives as a main sequence

  the force of the radiation pressure is balanced with the gravitational force in a stable star
• how long will a star stay on the main sequence

  depends on mass

  Small stars use less fuel so stay in equilibrium and will live longer

  large stars have more fuel to begin with, but need to use it all at a faster rate to stay in equilibrium so will live shorter
• red giant

  eventually, a star the size of our sun becomes a red giant the star keeps increasing in size until it runs out of hydrogen

  Heavier elements can then form

  The largest mass element formed is iron, but smaller elements will be created depending on the mass of the star

  Then fusion stops the gravitational force causes it to collapse in on itself creating a white dwarf the outer atmosphere is blown away
• white dwarf

  A red giant cools down to form a white dwarf
• planetary nebula

  the gas surrounding the white dwarf continues to glow creating a nebula that houses a white dwarf at the centre
• red dwarf

  forms when a white dwarf cools and reddens
• black dwarf

  red dwarf cools down more

  star stops growing
• supergiant

  once helium runs out heavier elements continue to fuse until iron is made and then it stops with no nuclear fusion. There is no radiation pressure outwards and the only force inwards gravity causing the start to collapse. This causes a supernova because the star is so big.
• supernova

  Super giant explodes blasting away out of layers called a supernova supernova make any elements heavier than iron because of the energy released the supernova returns material such as dust back into space
• neutron star

  this is a new star and what’s left behind is a dense core which collapses it is made from a supernova
• black hole

  if the start large enough a black hole can be produced leading to the death of a high mass star the core collapses completely and vanishes it is made from the supernova