Universe and Solar System Notes

UNIVERSE

  • Definition: It contains all galaxies, stars, and planets.
  • COSMOLOGY: branch of science studying the origin, evolution, and fate of the universe.

THEORIES ON THE ORIGIN OF THE UNIVERSE

  • BIG BANG
  • STEADY STATE
  • COSMIC INFLATION
BIG BANG
  • Very small, very hot state that expanded over time; peak around 13.7 billion years ago13.7\text{ billion years ago}; expansion continues to the present, age roughly 13 billion years13\text{ billion years}.
  • KEY FIGURES: Vesto Slipher (1910); Fr. Georges Lemaitre (1927) – Father of the Big Bang; Edwin Hubble (1929).
  • BEGINNING: Universe began with hot, tiny particles mixed with light and energy; expansion cooled; light elements formed (Hydrogen & Helium); stars formed; gravity formed galaxies.
STEADY STATE
  • Always expanding with a constant average density.
  • Matter is continuously created to form stars and galaxies.
  • No beginning or end in time; appearance remains the same despite expansion.
COSMIC INFLATION
  • Inflation: rapid expansion of space-time.
  • Early universe was a rapidly expanding bubble of pure vacuum energy; initially no matter or radiation.
  • Accepted because it explains puzzling observations from the Big Bang: homogeneity, flatness, and later formation of stars/systems.
  • PUZZLING OBSERVATIONS:
    • Homogeneity of objects in space.
    • Apparent flatness or smoothness.
    • Formation of stars and star systems later on; density fluctuations during expansion leading to gravity pooling gas into masses.

SOLAR SYSTEM

  • Definition: gravitationally bound system of the Sun and objects that orbit it.
  • Components: Sun, 88 planets, dwarf planets, asteroids, comets, meteors.
  • Mnemonic: My Very Excellent Mom Just Served Us Noodles.

ORIGIN OF THE SOLAR SYSTEM

  • MODEL: representation of an idea/process used to describe phenomena.
  • GEOCENTRIC MODEL: Claudius Ptolemy; Earth at the center; Sun, Moon, stars, and five planets orbited Earth.
  • HELIOCENTRIC MODEL: Nicholas Copernicus; Sun at the center.

FORMATION OF STAR SYSTEMS

  • NEBULAR HYPOTHESIS: Kant and Laplace; formed from rotating gas cloud (nebula) about 4.6 billion years ago4.6\text{ billion years ago}.

  • STAGES:

    • Self-gravity contracts the gas cloud
    • Conservation of angular momentum pulls cloud into a disk
    • Disk begins to rotate
    • Central mass forms (proto-Sun)
    • Centrifugal force balances gravity; rings form
    • Rings form into planets

  • THE PLANETISIMAL AND TIDAL THEORIES: proponents include Thomas Chamberlin and Forest Moulton; James Jeans; Harold Jeffreys; idea: tidal effects from a passing star influenced the Sun.

TERRESTRIAL VS JOVIAN PLANETS

  • TERRESTRIAL PLANETS: Mercury, Venus, Earth, Mars – solid surfaces, silicate rocks and metals.
  • JOVIAN PLANETS: Jupiter, Saturn, Uranus, Neptune – no solid surfaces; mainly hydrogen and helium.