1. Classical Astronomy Introduction
Mr. Conkey Astronomy

2. Geocentric vs Heliocentric System
Idea of a Geocentric universe introduced by Aristotle
Geocentric universe became divine fact
Nicolas Copernicus’ “new idea”
Galileo Galilei’s substantiation
Aristotle of ancient Greece was the first to present the idea of a geocentric universe, where the Earth was at the center of the universe and the sun and all other bodies orbited it. Despite proposals from other scientists (Aristarchus), geocentric universe had become accepted and protected by the Catholic church. Nicolas Copernicus then realized that retrograde motion could easily be explained if the Sun were in fact in the center of the universe, known as a heliocentric universe; he posed that it was a result of the differences between the time of Earth’s orbit around the Sun and the time it takes other planets to. He also stated that since Mars had the greatest retrograde motion then it must be the closest to Earth as compared to Jupiter and Saturn. His two other hypotheses of import include planets locations could be predicted due to circular orbits around the Sun, and that the Suns rising and setting was due to Earths rotation on its axis. Galileo Galilei used a small telescope that he constructed to view four moons orbiting Jupiter, which proved that Earth is not at the center of all orbital motion. A second observation he made was that Venus’ apparent size changed and had phases which could only be explained by both Earth and Venus being in a heliocentric orbit. Galileo also found that no matter their mass, gravity acts on falling objects with the same acceleration; along these lines he also determined that bodies will move and continue to do so if a force acts on them, and will only change direction or stop if another force is applied to them. (Merali, 2009). Picture: (Merali, 2009).

3. Kepler’s three Laws Calculated planet positions on elliptical orbits
Suggested a magnetic force affected objects
Calculated planet positions on elliptical orbits
Discovered three laws defining planetary motion.
Johannes Kepler suggested that there was a magnetic force from the Sun acting with greater force on the planets closer to it and a lesser on those farther away, as planets closest to the Sun move faster than those further away. He tried to calculate planetary positions using circular orbits with no success, and then switched to an elliptical one that worked. He developed three laws defining planetary motion including the law of ellipses (planets all have elliptical orbits with Sun at one focus), the law of equal areas (a line drawn out from planet to Sun sweeps out equal areas in equal amounts of time; orbital speeds differ), and the law of orbital harmony (the square of the orbital period of any planet is equal to the cube of the planets average distance from the Sun) (Merali, 2009). Picture (Universe, 2017)

4. Sir Isaac Newtons contribution
Unified planetary and satellite motions
Gravity
Sir Isaac Newton devised that gravity must extend from acting on an apple to acting on the Moon. He found that Earths gravitational attraction keeps the Moon in orbit around it instead of moving in a straight line through space. It was Newton who learned that gravity acts on all bodies (Merali, 2009). Picture: (Isaac, 2017)