The Sun as a Star

• The Sun lies at the centre of the Solar System

  • The Sun is a star which makes up over 99% of the mass of the solar system
  • The fact that most of the mass of the Solar System is concentrated in the Sun is the reason the smaller planets orbit the Sun
  • The gravitational pull of the Sun on the planets keeps them in orbit

  
• The Sun is a medium sized star consisting of mainly hydrogen and helium
• It radiates most of its energy in the infrared, visible and ultraviolet regions of the electromagnetic spectrum
• Stars come in a wide range of sizes and colours, from yellow stars to red dwarfs, from blue giants to red supergiants

  • These can be classified according to their colour
• Warm objects emit infrared and extremely hot objects emit visible light as well

  • Therefore, the colour they emit depends on how hot they are
• A star's colour is related to its surface temperature

  • A red star is the coolest (at around 3000 K)
  • A blue star is the hottest (at around 30 000 K)
• The colour of a star correlates to its temperature

  A) hottest

  B) coolest

  
• In the centre of a stable star, hydrogen nuclei undergo nuclear fusion to form helium

  • A huge amount of energy is released in the reaction
  • This provides a pressure that prevents the star from collapsing under its gravity
• The equation for the nuclear fusion reaction is shown here:

  
• The fusion of deuterium and tritium to form helium with the release of energy

  A) deuterium

  B) helium

  C) fusion

  D) tritium

  E) neutron

  F) energy

  
• Solar flares - ejections from sun

  • prominence - plasma bridge on the sun