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• The Greeks are very much noted for their major contributions in different fields. They were not only great philosophers, they were great scientists and mathematicians as well.
• It was in Greece that the Golden Age of early astronomy was centered.
• Geocentric view


  The Earth is the center of the universe and is a motionless sphere, with the sun, moon, Mercury, Venus, Mars, Jupiter, and Saturn orbiting the Earth
• Celestial sphere


  The transparent, hollow sphere located beyond the planets where the stars travel daily around the Earth
• Greek astronomers


  • Hipparchus
  • Aristarchus
  • Eratosthenes
  • Anaxagoras
  • Eudoxus
• Hipparchus


  • Observed the brightness of 850 stars and arranged them into order of brightness or magnitude
• Aristarchus


  • Proposed the first Greek heliocentric view, where the sun was much larger than the Earth and many times farther than the moon
• Eratosthenes


  • Made the first successful attempt to determine the size of the Earth by applying geometric principles
• Anaxagoras


  • Believed the Earth was spherical in shape since it always casts a curved shadow when it eclipses the moon
• Eudoxus


  • Proposed a system of fixed spheres where the sun, moon, five known planets and the stars were attached
• The Greeks used philosophical arguments and observational data to explain the movements of the stars and other heavenly bodies.
• The Greeks measured the sizes and distances of the sun and moon using geometry and trigonometry.
• Eclipses


  An obscuring of the light from one celestial body by the passage of another between it and the observer or between it and its source of illumination
• The moon eclipses the sun
• Oblate spheroid


  The shape of the Earth, with a bulging equator and squeezed poles
• Solstice


  Either of the two times in the year, the summer solstice and the winter solstice, when the sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days
• Heliocentrism


  The astronomical model in which the Earth and planets revolve around the Sun
• Geocentrism


  Any theory of the structure of the solar system (or the universe) in which Earth is assumed to be at the center of it all
• Around 500 B.C., most Greeks believed that the Earth was round, not flat
• Pythagoras and his pupils were first to propose a spherical Earth
• Anaxagoras supported Pythagoras' proposal through his observations of the shadows that the Earth cast on the Moon during a lunar eclipse
• Aristotle listed several arguments for a spherical Earth which included the positions of the North Star, the shape of the Moon and the Sun, and the disappearance of the ships when they sail over the horizon
• North Star


  Believed to be at a fixed position in the sky, but Greeks noticed it was closer to the horizon when traveling nearer the equator
• Shape of the Sun and the Moon


  Aristotle argued that if the Moon and the Sun were both spherical, then perhaps, the Earth was also spherical
• Disappearing ships


  If the Earth was flat, then a ship traveling away from an observer should become smaller and smaller until it disappeared, but Greeks observed the hull disappeared first before the sail as if it was being enveloped by the water
• Eratosthenes' method to measure the circumference of the Earth

  1. Observed the angle the Sun made with the vertical direction in Alexandria and Syene

  2. Hypothesized that the light rays coming from the sun are parallel, and the Earth is curved

  3. Computed the circumference of the Earth to be approximately 40,000 kilometers
• Anaxagoras


  • Explained what causes the phases of the moon, that the moon shone only by reflected sunlight and only half of it is illuminated at a time
• Eudoxus


  • Proposed a system of fixed spheres, with the Sun, the moon, the five known planets and the stars attached to these spheres which carried the heavenly bodies while they revolved around the stationary Earth
• Aristotle


  • Believed the earth is spherical in shape since it always casts a curved shadow when it eclipses the moon, and that the earth was the center of the universe with the planets and stars as concentric, crystalline spheres centered on the earth
• Aristarchus


  • The very first Greek to profess the heliocentric view, considering the sun as the center of the universe, and made an attempt to calculate the distance of the sun and the moon
• Eratosthenes


  • Made the first successful attempt to determine the size of the earth by applying geometric principles and observing the angles of the noonday sun in two Egyptian cities
• Hipparchus


  • Observed and compared the brightness of 850 stars and arranged them into order of brightness or magnitude, developed a method for predicting the times of lunar eclipses, and measured the length of the year to within minutes of the modern value
• Claudius Ptolemy


  • Developed the Ptolemic Model, which claimed that the planets moved in a complicated system of circles around the earth, the geocentric model
• Ptolemy's Ptolemic Model used epicycles and deferents to explain the retrograde motion of the planets
• Aristotle studied and used scientific methods to prove the Earth is spherical, including observations of the North Star, ships sailing over the horizon, and the shadow cast during eclipses
• If the Earth was not a sphere, life on Earth would be very different