ASTR500

• Our knowledge about the Universe and Nature is limited
• Science operates with


  Models and theories
• Testing models and theories

  1. Experiments (in Physics, Chemistry, Psychology, etc.)

  2. Observations (in Astronomy)
• Theory/model represents reality well if it possesses

  Explanatory and predictive power
• We can still be not 100% right about something
• The Universe consists of about 5% of matter, 27% of "dark matter" and 68% of "dark energy"
• Structure-Scale Ladder


  The difference between the largest object and the smallest object is 40 orders of magnitude in size and 80 orders of magnitude in mass
• Structure-Scale Ladder


  • Different forces (gravity, electro-magnetic, nuclear) keep matter together to form structures
• Light-year


  The distance that light travels in one year
• Observable Universe


  • The speed of light is finite, so it takes time for photons (light) emitted by a remote object to reach us
  • Looking out in space = Looking back in time
  • Telescope is a time machine
  • The age of the Universe is not infinity, but "just" 13.8 billion years
  • There are objects that are located some 100 and 1000 billion light-years away, but we cannot see them
• Cosmic Microwave Background Radiation (CMB)


  • The most remote object we observe in the Observable Universe, with an age of about 13.8 billion years and a temperature of 3000 degrees (Kelvin)
  • We can "see" it only in the form of radio waves due to the redshift caused by expansion of the Universe
• By analysing the CMB, we can find that the age of the Universe is 13.8 billion years
• Galaxies


  • Consist of stars and contain large amount of the dark matter
  • Our Galaxy, the Milky Way, looks like a CD or DVD - a flat thin disc
  • There are 200 billion stars in the Milky Way
• There are 200 billion galaxies inside the Cosmological horizon
• Cosmic Web


  • Billions of galaxies in the observable universe form a "cellular structure" - walls, filaments, and voids
  • The dark matter plays the decisive role in formation of this structure, because the dark matter makes the most of the mass of the cosmic web
• Virgo Supercluster


  The Local Group of galaxies, which includes the Milky Way and the Andromeda Galaxy (M31) as the biggest members