SCI ♡ Greek Astronomers

Anaxagoras

• explained what causes the phases of the moon

  • moon shone only by reflected sunlight

  • since it is sphere, only half of it is illuminated at a time

  • this illuminated part that is visible from earth changes periodically

Hipparchus

• greatest of the early greek astronomers

• observed and compared the brightness of 850 stars

  • arranged them in order of brightness or magnitude

• developed a method for predicting the times of lunar eclipses within a few hours

Claudius Ptolemy

• proposed the geocentric model (ptolemic system)

  • sun, moon and other planets move in circular orbits around the earth

  • earth was the center of the universe

  • the planets moved in a complicted system of circles

    

Eratosthenes

• first successful attempt to determine the size of the earth by applying geometric principles

  • 40,250 to 45,900 kilometers (25,000 to 28,500 miles)

  • by comparing the sun's relative position at two different locations on the earth's surface

Aristotle

• student of Plato

• earth is spherical in shape

  • since it always cast a curved shadow when it eclipses the moon

• believed that the earth was the center of the universe

• planets and stars were concentric crystalline sphere centered on the earth

Nicolaus Copernicus

• Polish astronomer & mathematician

• proposed that the sun is at the center of the solar system in 1543

• called the heliocentric model

  • the Sun is stationary at the center of the universe

  • the Earth and other planets revolve around it