1. History of Astronomy

2. Early Astronomy Astronomy Is science that the universe Greeks 600 B.C. – A.D. 150 Measured distances to the Sun and Moon

3. Eratosthenes  Successfully Measured the circumference of the Earth  1.7% Error 2400 Years Ago

4. Geocentric View  Pre 300 B.C.  Earth is the center of the Univerese  The orbs (Sun, Moon, Mercury, Venus, Mars and Jupiter) orbit the Earth each day  Surrounded by a Hollow Sphere

5. Heliocentric Aristarchus (312-230 B.C.) Earth and the other planets orbit the sun Dominated Western Thought for over 2000 Years

6. Ptolemaic System Ptolemy (A.D. 141) Believed in Geocentric Model Observed Retrograde Motion – Planets Move to the East, but periodically they stop and reverse direction Social Bias in Science

7. Modern Astronomy Renaissance of Science Broke Away from Religious and Philosophical Views Used Natural Laws to explain the motions of the Heavens

8. Modern Astronomy Nicolas Copernicus 1473-1543 Earth is a Planet Sun Centered Planets Orbited the Sun in Complete Circles

9. Modern Astronomy Tycho Brahe 1546 -1601 Spent 20 yrs. Measuring the Locations of the Heavenly Bodies Johannes Kepler 1571-1630 Assistant to Brahe Discovered 3 Laws of Planetary Motion – Ellipse Determined the Distance from the Sun to Earth is 1AU = 150 Million km

10. Modern Astronomy Galileo Galilei 1564 – 1642 Major Contribution was the behavior of the Moving Objects Ground Lenses to make telescopes Made Discoveries that supported Heliocentric View Sir Isaac Newton 1642-1727 Expanded on Galileo Force Formulated and tested the Law of Universal Gravitation at the age of 23 This is the force that makes planets revolve in a circle