Astronomy

• Geocentric Theory

  • aristotle
  • ptolemy
  • brahe
  • plato
• Heliocentric theory

  • Copernicus
  • galileo
  • aristarchus
  • kepler
• Plato (428-348 BCE)

  • universe is perfect or ethereal and unchanging
  • stars = eternal and divine
• Exodus of Cnidus (390 - 337 BCE)


  there are 27 interconnected spheres
• Aristotle (384-322 BCE)


  in conjunction to Eudoxus model, he added 3 spheres to Jupiter and Mars; 4 spheres to sun, moon, venus, and mercury
• Claudius Ptolemy (90-168 CE)

  1. Earth is a spherical object.
  2. The stars are fixed bodies attached to a solid spherical exterior part of the universe.
  3. Planets move independently of the fixed stars, and sometimes, the planet seems to reverse its motion.
• Aristarchus of Samos (310-230

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  • stated that sun and stars are fixed.
  • Estimated the sizes of the Sun and Moon as compared to Earth's size (Moon's diameter was 0.32-0.40x the diameter of Earth and the Sun's diameter was 6.3-7.2x the diameter of Earth).
  • Estimated the distances from the Earth to the Sun and Moon (sun is about 18-20x farther away from Earth than moon).
• Pythagoras


  first one to originate a spherical earth using observations such as: North and South Constellations; Sinking Ships; and Lunar Eclipse.
• Plato


  The earth is a form of globe having its extremes in every direction

  equidistant from the center.

  The planet is:

  • At the center of universe

  • Perfect and eternal

  • Has four elements
• Aristotle


  His work on 350 BC entitled, "On the Heavens" initiated the idea of a geocentric universe with fixed spherical earth at its center.

  
  

  Three Arguments:

  1. Rounded shadow which the earth projects on the moon
  2. Change in the constellations as travelers voyage to southern and northern regions
  3. Indirect idea on gravity
• Eratosthenes


  Ancient scholars tried to provide proof of a spherical Earth

  and its circumference through calculations. It was Eratosthenes who gave the most accurate size (through non-scientific calculations) during their time.
• geocentric 


  earth is the center of the universe
• heliocentric


  sun is the center of the universe
• Modern Astronomy


  2 major distinct characteristics that differentiate it from ancient are:

  1. The observations became more quantitative in nature.
  2. The theories formulated are based on logical mathematical concepts
• Nicolaus Copernicus (1473-1543)


  He corrected the Geocentric theory and proposed the Heliocentric Theory with the following postulates:

  1. Earth is considered as only one of the planets.
  2. Earth rotates on its axis daily and revolves around the sun once a year.
  3. Earth experiences an annual tilting of its axis.
  4. The retrograde motion of the planets explained by earth's motion.
  5. The distance from earth to sun is small compared to earth's distance from the stars.

  Tilting of the Earth and the four seasons.
• Tycho Brahe (1546-1601)

  The following are his important contributions to modern astronomy:

  1. modified the geocentric model of the universe.
  2. designed and built huge instruments used to make precise measurements of the positions of the planets.
  3. discovered supernova in the constellation Cassiopeia in 1572.
  4. made observations of planetary motions that are important to the development of Kepler's Laws and other models of the solar system.
  5. Tychonic System
• Galileo Galilei (1564-1642)


  Using his telescope, the following are what he observed:

  1. discovered sunspots and rough surface of the moon.
  2. discovered the 4 famous moons of Jupiter known as Galilean moons (lo, Europa, Ganymede, Callisto).
  3. discovered that Venus has phases like moon.
• Johannes Kepler (1571-1630)


  First Law

  It states that the orbits of the planets are ellipses, with the sun at one focus.

  Second Law

  It states that an imaginary line drawn from the sun to a planet sweeps out equal areas in equal intervals

  • PERIHELION: Nearest to the sun
  • APHELION: farthest from the sun

  Third Law

  The cube of the radius of the orbit of a planet around the sun is proportional to the square of its period of revolution