pysics 2.0

• Universe


  A large collection of billions of galaxies
• Galaxy


  A large collection of billions of stars
• Solar system


  A collection of planets orbiting a common star. Our solar system is in the Milky Way galaxy

  
• Gravitational field strength


  The force per unit mass on a body in a gravitational field, measured in Newtons per kilogram (N/kg). It varies with the mass and size of the body
• Orbits


  • Moons orbit planets in slightly elliptical orbits with near constant orbital speed
  • Planets and comets orbit the Sun, with planets in slightly elliptical orbits and comets in highly elliptical orbits
  • Artificial satellites orbit the Earth

  
• Orbital radius or time period

  The greater the orbital radius or the smaller the time period, the greater the orbital speed
• Comet speed


  Comets have a greater speed nearer to the star (when r is smaller) because the ice inside them melts as they get closer (& warmer) - causing their mass to decrease
• Star classification


  Stars can be classified according to their colour, which is related to their surface temperature - hotter stars are bluer, cooler stars are redder

  
• Absolute magnitude


  The apparent magnitude a star would have if viewed from 10 parsecs (32.6 light-years) away
• Apparent magnitude


  How bright a star appears at a particular point in space
• Hertzsprung-Russell diagram


  • Shows the relationship between a star's surface temperature and brightness, with main components being supergiants, red giants, main sequence, and white dwarfs

  
• Big Bang theory


  States that the universe expanded outwards from a single point
• Evidence for Big Bang


  • Red shift of light from galaxies showing they are moving away, with those furthest away moving fastest
  • Cosmic microwave background radiation present throughout the sky
• Doppler effect


  If a wave source is moving relative to an observer, there will be a change in the observed frequency and wavelength
• Red-shift


  Doppler shift is responsible for the red-shift of light from galaxies moving away from Earth, with the faster they are moving, the more their light is red-shifted