1. Geocentric Model the Earth is the center of the solar system

2. Heliocentric model – sun is the center of our solar system

3. Ptomely, Copernicus, Tycho Brahe and Kepler... Ptolemy devised widely-accepted theory to explain apparent motion of Sun and planets across sky. But... basic model could not explain retrograde motion (reverse motion of planets) of planets so several modifications were introduced...The Ptolemaic System

4. Copernicus.. Polish canon Nicholas Copernicus (1473-1543) worked on a Sun-centred or heliocentric model of the solar system from 1503 onwards Heliocentric model was no simpler than the prevailing Ptolemaic system but did do away with equants and allowed the order of the planets from the sun to be deduced unambiguously.

5. The Heliocentric model: –partly explained the retrograde motion of the planets –could not predict their exact locations, but ephemerides based on Copernicus (Prutenic Tables) were much more accurate then those based on Ptolemaic system (Alfonsine Tables).

6. Tycho Brahe.. Tycho Brahe (1546-1601), Danish nobleman, founded modern observational astronomy Motivated by the fact that a conjunction of Jupiter and Saturn predicted by Prutenic Tables (Copernican model) was in error by 2 days Attempted to measure the distance to Mars by parallax method – unsuccessful but his detailed observations provided the raw data for Kepler to develop his laws of planetary motion

7. Nova (1572) – overturned Aristotelian view of perfect, unchanging Universe. Comet (1577) – Tycho demonstrated that comets were celestial not atmospheric objects –cometary orbit took it through crystal spheres on which celestial object were assumed to be fixed, hence crystal spheres do not exist.

8. Kepler... In the early 1600s Johannes Kepler (1571- 1630), German mathematician, finally produced three laws of planetary motion: Kepler’s laws. Worked with Tycho Brahe from 1600-1601 and on Brahe’s death took over his observatory Using Tycho Brahe’s observations of Mars he was able firstly to deduce his equal area rule (K2), then that the planet had to have an elliptical orbit (K1).