Astro Physics

• Order of Astrophysics objects

  • moon < planet < star < solar system < galaxy < universe
• Orbit


  The curved path of a planet or other body around a star, planet, or moon
• Types of orbits


  • planets orbit stars
  • stars orbit galaxy’s
• Planets have almost circular orbits
• Comets have elliptical orbits
• Lifecycle of stars


  • Nebula
  • Protostar
  • Main sequence
  • Red giant
  • Supernova
  • White dwarf
  • Black hole
• Stellar properties


  • Colour
  • Temperature
• Our sun is an orange main sequence star
• The formula for orbital period is T = 2πr/v
• The formula for orbital velocity is v = 2πr/T
• When is the comet moving the fastest?

  when it reaches the sun
• Colours of stars and their temperatures / (hottest) Blue < white < yellow < orange < red (coldest)
• Universe


  Collection of billions of galaxies
• Galaxy


  Collection of billions of stars
• Orbits


  1. Moons orbit planets

  2. Planets orbit stars
• Orbits


  • Slightly elliptical
• Orbits are almost gravitational pull
• Moon orbits Earth
• Comet


  • Lumps of ice/rock that orbit the Sun
  • Highly elliptical orbit
  • Fastest when closest to the Sun
• Sun has the strongest gravitational pull
• Orbiting objects


  • Constantly changing direction
  • Constantly accelerating
• A force must be acting = centripetal
• Instantaneous velocity
• Gravitational field strength


  • Depends on mass of planet/star
  • Depends on velocity
  • Depends on distance from the object
• The greater the gravitational pull, the faster you need to go to stay in orbit