Understanding Light Years

Light Year

• Light year is a unit of distance measurement, not time.
• Light travels at approximately 186,000 miles per second (300,000 kilometers per second).
• One light year equals the distance light travels in one year: about 5.87 trillion miles (approximately 9.46 trillion kilometers).

Big Bang Theory

• The universe originated from a hot explosion known as the Big Bang.
• Post-Big Bang conditions were primarily radiation; as the universe cooled, hydrogen and helium formed.
• Evidence supports the Big Bang theory:
  • The universe is believed to have had a definitive beginning.
  • Hubble's Law indicates that galaxies are moving away, suggesting universal expansion from a compact state.
  • In 1965, Cosmic Microwave Background radiation (CMB) was discovered, measuring about 2.725 K, indicating remnants of heat from the Big Bang.
  • The observed abundance of hydrogen and helium aligns with predictions of the Big Bang model.

Planet Formation

• Planets and stars form from the same primordial gas and dust cloud.
• Observations of T Tauri stars show planet formation in dust disks around them.
• The solar nebula, a spinning disk, was where the solar system (including the Sun) formed approximately 5 billion years ago.
• The formation process involves:
  • The solar nebula contracting and flattening.
  • The central mass becoming the Sun and smaller masses potentially forming jovian planets.
  • Dust grains acting as condensation nuclei, leading to moon-sized planetesimals.
  • The expulsion of gaseous nebula by strong solar winds.
  • Continued collisions among planetesimals forming larger planets with circular orbits.

Relationship between Theories

• The Big Bang theory discusses the creation of matter and energy in the universe.
• The Solar Nebula theory addresses how that matter evolves into galaxies and solar systems.