Astronomy chapter 1

• All matter in the Universe is organised in structures, which form a hierarchy
• Structure-scale ladder


  Sequence of structures of different scales from the greatest down to the smallest
• Worlds based on size

  • Megaworld (from Greek megas - great, grandiose)
  • Macroworld (Greek makros - big, large)
  • Microworld (Greek mikros - small)
• Objects in the Megaworld

  • Stars
  • Planets
  • Galaxies
• Objects in the Macroworld

  • Objects surrounding us in everyday life, objects commensurate to us
• Objects in the Microworld


  • Elementary particles
  • Atoms
  • Molecules
  • Cell
  • Chromosome
• Living objects can be referred both to macro- and microstructures depending on their size
• Structure-scale ladder


  • Observable Universe
  • Cellular structure (voids, walls, superclusters of galaxies)
  • Clusters and groups of the galaxies
  • Galaxies, quasars and galactic nuclei
  • Stellar clusters in galaxies
  • Stars, planetary systems
  • Cosmic bodies: planets (incl. the Earth), comets, asteroids, etc.
  • Geological structures (tectonic plates, continents, islands, mountains, etc.)
  • Macroscopic objects (including us)
  • Microscopic objects (cells, genes, etc.)
  • Molecules
  • Atoms
  • Atomic nuclei and elementary particles
  • Quarks, leptons, messenger particles
• Light-year


  Distance travelled by light in vacuum in one year, approximately 10 million million kilometres = 10 to the power 13 km
• Cosmological horizon


  Border of the observable Universe, beyond which matter is not accessible to observations
• In a static Universe, the cosmological horizon would be situated at the distance that light travels within the age of the Universe, which is about 46 billion light-years in our expanding Universe
• Distribution of galaxies on the sky is both regular and non-regular
• Cosmic web


  Galaxies form cells similar to a honeycomb, with walls formed by galaxies and empty spaces (voids) inside the cells. Majority of galaxies are concentrated in the intersections of walls and in the knots where three walls intersect
• Clusters of galaxies


  Nearly spherical structures consisting of hundreds and thousands of galaxies
• Groups of galaxies


  Non-numerous clusters of galaxies, such as the Local Group consisting of the Milky Way and Andromeda Galaxy
• Galaxies


  • Stellar systems consisting of billions of stars, gas and dust. 9/10 of the galactic material exists in a hidden, invisible form
• Masses of galaxies vary from 10^9 to 10^12 solar masses, with the Milky Way being close to the upper limit
• Sizes of galaxies (their visible parts) usually vary from 3 to 300 thousand light-years
• Types of galaxies


  • Spiral
  • Spherical or elliptical
  • Irregular asymmetric
• Quasars


  Quasi-stellar objects, which are the most distant objects in the observable Universe and are likely the nuclei of distant galaxies in a highly active state
• Types of stellar clusters

  • Globular clusters
  • Open clusters
• Globular clusters


  • Spherical objects containing millions of stars, the oldest formations in the Milky Way with an age of 10-12 billion years
• Open clusters


  • Contain tens, hundreds or thousands of stars, some are relatively young (e.g. Pleiades at 60 million years)
• Stars are born in groups and clusters, not one at a time
• Types of stars


  • Regular stars
  • Compact stars (white dwarfs, neutron stars, black holes)
• Sizes of regular stars vary from slightly smaller than the Sun to enormous sizes of supergiants, while compact stars range from several kilometres to several thousand kilometres
• Planetary systems


  Apart from the Solar system, hundreds of multiplanetary systems with at least two confirmed exoplanets are known
• The star with the most confirmed planets is the Sun with 8, while Kepler-90 and HD 10180 have the most exoplanets with 7 each
• Cosmic bodies


  • Planets
  • Comets
  • Asteroids
  • Small planets
• The diameter of the Earth is about 13,000 km
• Macroscopic bodies are all the objects around us, consisting of a very large number of molecules
• Microscopic bodies


  Associations of molecules, such as cells and their components
• Molecules


  • Vary in size from the simplest two-atomic molecules to complex polymeric macromolecules with molecular weights in the hundreds of thousands
• Atom


  Consists of a compact nucleus and an electron shell, with the size determined by the electron shell
• The word "atom" comes from the Greek word "atomos" meaning indivisible, but atoms were later found to be composed of subatomic particles
• Subatomic particles


  • Elementary particles (primary, indivisible)
  • Composite particles
• Initially only protons, neutrons, electrons and photons were considered elementary particles, but more were discovered over time
• Types of subatomic particles

  • Elementary particles
  • Composite particles
• Elementary particles


  Primary, indivisible particles, of which all the matter consists
• Till the beginning of 1930s the only known representatives of elementary particles were proton, neutron, electron, and photon