Universe

• What did the ancient Greeks believe about the Solar System?

  The Earth was the center of the Solar System
• What is the geocentric model of the Solar System?

  • Earth is at the center
  • Sun, Moon, planets, and stars orbit Earth
  • Orbits are in perfect circles
• Why did the geocentric model persist for so long?

  People felt stationary and observed celestial movements
• What model replaced the geocentric model?

  The heliocentric model
• What did Galileo contribute to the understanding of the Solar System?

  He provided evidence against the geocentric model
• How did Galileo's observations of Mars challenge the geocentric model?

  He observed varying movements of planets
• What is the heliocentric model?

  Planets revolve around the Sun
• What shape are the orbits of planets in the current model?

  Elliptical, not perfect circles
• What does the current model say about the Sun's position in the universe?

  The Sun is not at the center of the universe
• What are the two main theories for the creation of the universe?

  1. Steady State Theory
  2. Big Bang Theory
• What does the Steady State theory propose about the universe?

  The universe has always existed as it is now
• How does the Steady State theory describe the density of the universe?

  The density remains roughly the same
• What happens to matter in the Steady State theory as the universe expands?

  New matter is constantly being created
• What does the Big Bang theory state about the initial state of the universe?

  All matter occupied a very small space
• What occurred after the initial explosion in the Big Bang theory?

  Space started expanding
• What is the estimated age of the universe according to the Big Bang theory?

  Around 13.8 billion years
• What is the current acceptance of the Big Bang theory?

  It is the accepted theory of the universe's origin
• What are the key differences between the Steady State and Big Bang theories?

  • Steady State: Universe is eternal, no beginning or end
  • Big Bang: Universe has a finite age, started with an explosion
• What should you be able to describe regarding the theories of the universe?

  Each theory and its comparison to current ideas
• What is the main observation that suggests the universe is expanding?

  The universe looks like it's getting bigger