PHYSCI 4Q

• Three reasons why there is no absolute truth: limitations in information, religion, popularity
• The first description that the earth was flat was from ancient writings.
• Nowadays, we believe that the sun is the center
• Early people believed that the earth is the center of the universe.
• In 5,500 BC, ancient Armenian astronomers used the Carahunge Observatory to mark movements of the sun, moon, stars.
• Thales of Miletus believed the Earth was a disk floating on water, just like ships floating on water.
• Thales is the first one to use observations and hypotheses to explain phenomena about nature
• Anaximander refined Thales’ idea. The shape of the Earth is like a cylinder, with a height ⅓ of its diameter. The earth is rounded and circular with two plane surfaces.
• Anaximenes

  • Earth was formed by air.
  • Felting process
  • Earth began as a flat disk that floats on air.
• Empedocles

  • 5th century B.C.
  • Heaven is spherical and crystalline.
  • Stars are patches of fire.
• Anaxagoras

  • First developed the idea of Lunar eclipse
  • Earth is in the middle of sun and moon.
  • Earth makes a circular shadow on the moon's surface, hence Earth is spherical.
• Pythagoras

  • First to propose a spherical Earth.
  • The sphere is a perfect shape.
  • He was the first one to originate a spherical earth using observations
• Pythagoras' observations of a spherical earth are:

  North and South Constellations

  Sinking ships

  Lunar eclipse
• NORTH AND SOUTH CELESTIAL POLES CONSTELLATIONS

  • North Star was believed to be at a fixed position in the sky.

  When Greeks traveled to places nearer the equator, like Egypt, they noticed that the North Star was closer to the horizon.
• SINKING SHIPS

  • If the Earth was flat, then a ship traveling away from an observer should become smaller and smaller until it disappeared.

  However, the Greeks noticed that the ship becomes smaller and then its hull disappeared first, before the sail as if it was being enveloped by the water until it completely disappeared.
• PARTIAL LUNAR ECLIPSE

  • The Earth casts the shadow on Earth
  • The shadow is curved, hence the Earth is curved.
• The Music of Sphere of Pythagoras - The motion of planets is related to musical sounds and numbers (mathematically).
• Pythagorean Model

  • Central fire is not seen because it is blocked.
  • First non-geocentric model
  • Earth is round
  • Heavenly bodies move in a circle.
  • Earth is at rest at the center, and everything rotates around it.
• According to Plato, sphere was the perfect shape
• Plato's Model

  • Geocentric model
  • He quoted that the earth is a form of a globe having its extremes in every direction equidistant from the center
• Plato

  • Earth doesn’t move, and everything moves around it in orbits.
  • He believed that the universe if perfect, ethereal, and unchanging.
  • He described the stars embedded in space as eternal and divine.
• Saving the Appearances by Plato

  • What uniform and ordered circular motion must be assumed for each planet to account for their apparently irregular annual paths.
• Eudoxus introduced a homocentric model wherein celestial spheres share on a common center: Earth
• Eudoxus

  • Cosmic spheres (sun, moon, stars) are around Earth.
  • Earth and (5) other planets: Mercury, Venus, Mars, Jupiter, Saturn
  • There are 27 interconnected geocentric spheres.
• Eudoxus introduced retrograde motions
• Retrograde motions show west to east motion
• North star is also called Polaris
• • Ether caused the movements of spheres / prime movers.
• According to Aristotle, Earth is stationary
• Aristotle, on the basis of Eudoxus’ model, added 3 spheres to Jupiter and Mars; 4 spheres to the Sun, Moon, Mercury, Venus.
• Aristotle

  • Spheres maintain the same distance from Earth and move constantly.
  • Sinama niya ang 4 elements of the universe and they have their own spheres: Air, Fire, Earth, Water
  • He proved that the earth is spherical
• Eratosthenes

  • He tried to estimate Earth’s circumference

  Measured the length of the shadow cast by a vertical stick
• Eratosthenes stated that the circumference of Earth is 40,000 KM.
• Deferent -circular path which planets move
• Epicycles - small spheres/paths or circles where planets move
• Equant -a point close to the orbit’s center.
• Prograde - east to west motion
• Retrograde - west to east motion
• Aristarchus was the first to place the sun at the center of the universe.
• Aristarchus Model

  • Sun is bigger than Earth hence it should be the one in center.
  • Moon orbits Earth, and Earth orbits the Sun.

  Stars are far from orbitations because of the absence of stellar parallax