# The Prelude - # The Geocentric Model - discovered by ptolemy - has the earth in the center; the sun, planets and stars orbiting around us in 'shells' - disproved! e.g moons of jupiter orbiting jupiter! --> disproved by THAT. observation of venus showed phases of venus, GALILEO'S BOAT EXPERIMENT - character called salvati - "what can we determine from the motion of the ship " # The Heliocentric Model