Missing u

• Flat Earth Model


  Old belief that the earth is plane or discoidal in form
• Flat Earth Model


  • According to Egyptians, Mesopotamians, and Homer
  • According to Israelites
• Spherical Earth Model


  Introduced by Pythagoras in the 6th century BC
• Arguments for a spherical Earth

  • Earth was spherical since the moon and the sun were both spherical
  • The North Star is closer to the horizon for places nearer the equator
  • When the ship sailed, the hull disappeared first, which implied that the surface of the earth was curved
• Modern Evidence Supporting Spherical Earth Model


  • Satellite photos show the earth is spherical
  • Astronauts in satellites orbiting in low Earth orbit personally observed curvature of the planet
  • Lunar eclipse shows a dark circle on the moon indicating a spherical earth
  • Time zones can only be explained if the world is round and continuously rotating on its axis
  • Airplanes can travel in a straight line without falling off any edges and circle the earth without stopping

  
• Astronomical Observations before the Advent of Telescopes


  Observations of the sun, moon, lunar eclipse, solar eclipse, daily and annual motion of the stars, constellations, and planets Mercury, Venus, Mars, Jupiter, and Saturn
• Earliest Astronomical Observations


  • Nebra sky disk from Northern Europe dated 1600 BC
  • Petroglyph showing the 1006 AD supernova that resulted in the Crab Nebula
  • Babylonian records dated 1600 BC trying to record positions of planets and time eclipse events
  • Evidence from Chinese, American, and European cultures like the Stonehenge

  
• Hellenistic Observations


  • Thales used Babylonian data to predict eclipses
  • Eratosthenes introduced the spherical Earth model and calculated the circumference of the earth
  • Plato introduced the geocentric solar system model
  • Heraclides presented the first solar system model with the earth at the center
  • Aristarchus presented the heliocentric solar system model with the sun at the center

  
• Renaissance and Astronomical Observations

  • Nicolaus Copernicus reintroduced the heliocentric theory
  • Tycho Brahe made accurate measurements of planetary and star positions
  • Johannes Kepler used Brahe's data to formulate the laws of planetary motion
  • Galileo Galilei pioneered astronomical observation and constructed the first small refracting telescope
• Kepler's Laws of Planetary Motion


  1. Law of Ellipses: Planets orbit the sun in elliptical paths with the sun at one focus

  2. Law of Equal Areas: The line from the sun to the planet sweeps out equal areas in equal time intervals

  3. Law of Harmonies: The ratio of the squares of the orbital periods to the cubes of the average distances from the sun is the same for all planets
• Kepler's laws explain the motion of planets around the sun
• Kepler's laws corrected conflicts on epicycles in the heliocentric theory by introducing elliptic orbits