Understanding the cosmos

• Gnomon (shadow caster)


  Babylonian and egyptian civilizations used this primitive version of a sundial to systematically observe the motion of a sun. By looking at the shadows that it casts, they were able to observe that the sun rises in the east and reaches the highest point in midday and sets in west.
• Phases of the moon

  • Ancient people have observed that the moon changes its path and its appearance within a period of 29.5 days.
  • They observed that the moon changes its appearance from thin semicircular disk to full circular disk.
  • These phases of the moon are the basis for ancient calendars
• Lunar eclipse


  • Besides their observation in the different phases of the moon they also notice that there are times when the moon or part of it seem to be covered by a shadow for a moment
  • This occurs when the earth casts its shadow on the moon when the earth is between the sun and the moon.
  • The moon changes into a dark or blood red color
• Solar eclipse


  • It occurs when the moon is in between the sun and the earth
  • The moon partially or completely blocks out the sun
• Motion of the stars

  • It was also observed that the stars appear to be attached to a celestial sphere that rotates around an axis in one day
  • This axis intersects the celestial sphere at the point in the northern sky and is presently close to the northern star, polaris
  • The constellations positions in the night sky vary depending on the time of the year
• Visibility of the planets

  • Astronomers have discovered that mercury venus mars and jupiter and saturn are planets because they have noticed that the stars are in a fixed position with respect to each other.
  • However there are very bright stars that change positions periodically
  • These stars do not belong to any group of constellations in the sky so they are called "wanderers"
• Nikolaus Copernicus


  Heliocentric theory
• Claudius Ptolemy


  Geocentric theory
• Tycho Brahe


  He developed his own model of the cosmos where planets orbiting the sun but the sun is orbiting the earth
• Johannes kepler


  He proposed three laws of planetary motion (ellipses, equal areas, harmonies)