Geography; Evolution of universe, Galaxy

  • Study of universe is called cosmology.
  • Galaxy = stars + planets + gases + dust.
  • Our nearest galaxy is Andromeda.
  • Milky Way contains 300 billion stars.
  • In AD 140, Ptolemy gave theory that earth is at the centre of the universe and sun and the other heavenly bodies revolve around.
  • In 1543, Copernicus stated that sun is at the centre of the universe and not earth.
  • Kepler supported Copernicus but said that sun is centre of the solar system not universe.
  • In 1924, Edwine Hubble first demonstrated existence of galaxies beyond Milky Way.
  • Structurally galaxies are found in three forms.
    • Spiral: – Have a central nucleus with great spiral arm. E.g. Milky Way and Andromeda.
    • Irregular: – With no shape.
    • Elliptical: – Without spiral arm.
  • Evolution of universe-
    • Big bang theory:- By Georges Le Maitre.( explosion occurred 13.8 billion years ago)
    • Steady state theory: – By Bondi, Gold and Fred Hoyle. ( it has no beginning and no end)
    • The pulsating theory: – At present universe is expanding.
  • Components of solar system-
    • Sun, eight planets and their respective satellites.
    • Interstellar debris such as asteroids, meteroids, comets.
    • Electrically charged gases called plasma.
    • Inter planetary dust particles.
    • And small solar system bodies (SSSB).( other than planets, dwarf planets and satellites)
  •  Various theories were given to explain origin of solar system-
PlanetesimalChamberline and Moulton
TidalSir James jeans and Harold jeffreys
Binary starH n Russell
SupernovaF hoyte
Inter stellar dustOtto Schmidt
ElectromagneticH Alfven
ProtoplanetG kuiper
Nebular cloudDr Von weizsacker
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