modern astronomy

• 2 major distinct characteristics of modern astronomy:

  • the observations became more quantitative in nature.
  • the theories formulated are based on logical and mathematical concepts.
• Nicolaus Copernicus corrected the geocentric theory and proposed the heliocentric theory with the following postulates:

  1. Earth is considered 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. earth's motion explains the retrograde motion of the planets
  5. the distance from Earth to sun is small compared to Earth's distance from the stars
• Nicolaus proposed the heliocentric theory by:

  • Earth is considered to be only one of the planets Earth rotates on its axis daily and revolves around the sun once a year.
  • earth experiences
• nicolaus copernicus

  • tilting of the earth and the four seasons
• Tycho Brahe

  1. he modified the geocentric model of the universe
  2. built massive instruments used to make precise measurements of the positions of the planets
  3. discovered a 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

  1. he discovered sunspots and rough surface of the moon
  2. discovered the four famous moons of Jupiter
  3. venus has phases like moon.
• known as the galilean moons 


  lo, europa, ganymede, callisto
• johannes kepler

  • first law states that the planets' orbits are eclipses with the sun at one focus
  • second law- an imaginary line drawn from the sun to a planet sweeps out equal areas in equal intervals
  • 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.
• periphelion


  nearest to the sun
• aphelion


  farthest from the sun