2. What is the purpose behind Astronomy? Explore the unknown beyond our atmosphere Track planets, satellites (moons), stars, comets Keeping time = Calendar Navigation Agriculture Religious beliefs

3. Claudius Ptolemy Greek Astronomer Expanded upon Aristoltes’s theories with mathematical calculations Ptolematic theory Earth Centered Solar System Geocentric Geo = Earth Centric = middle, center

4. Geocentric Model Geocentric model

5. Nocilaus Copernicus 1543 A.D. Published Heliocentric Theory Helio = Sun, Centric = Middle Heliocentric model Theory was not popular especially with religious organizations

6. Tycho Brahe Favored the geocentric model Brahe Geocentric Model Sun and moon orbit Earth All other planets orbit the Sun

7. Johannes Kepler Worked as Brahe’s assistant Formulated 3 laws of Planetary motion 1 st = Orbits are an ellipse 2 nd = Planets move faster closer to sun 3 rd p²=a³ Favored Heliocentric Model Sun not exact center of orbits

8. Galileo Galilei Used telescope to observe celestial bodies Discovered Galilean Moons of Jupiter, sunspots, physical features on moon Favored Heliocentric model Used phases of Venus to support model

9. Isaac Newton Explained the force that allows planets to orbit around the sun That force is…….. Gravity