1. Origin of Modern Astronomy

2. Key Terms 1. Astronomy – It is the science that studies the universe. It includes the observation and interpretation of celestial (spatial) bodies and phenomena. 2. Geocentric Theory - Earth centric Universe 3.Heliocentric Theory – Sun centric Universe 4. Gravity - the force that attracts a body toward the center of the earth, or toward any other physical body having mass. 5. Inertia – The tendency of an object to resist a change in motion. 6. Observatory – A building that contains one or more telescopes.

3. Geocentric Theory Ancient Greece

4. Geocentric Model: Ptolemy (87-150 AD) Used epicycles to explain planetary movements

6. The Birth of Modern Astronomy Copernicus - 1473-1543  Suggested a model that the Sun was the center of the universe.  This model explained the retrograde motion of planets better than the geocentric model.

7. Heliocentric Theory

9. The Birth of Modern Astronomy  Tycho Brahe  Johannes Kepler Tycho Brahe - 1546-1601  the greatest of the pre- telescope observers in Europe.  His measurements about the, positions of Sun, Moon and planets, especially of Mars, were far more precise than any made previously.

10. Kepler was an assistant to Tycho Brahe. He used Brahe’s observations to study the orbit of Mars Discovered three laws of planetary motion: predict with accuracy the motions of the planets. Johannes Kepler - 1609

11.  first scientist to use a telescope to observe the sky.  observed the phases of Venus and the moons of Jupiter. Both observations supported the heliocentric model. Galileo - 1564-1642

12. Sir Isaac Newton – 1642-1727  English scientist  explained gravity as the force that holds planets in orbit around the Sun.

13. Gravity’s Influence on Orbits

14. Gravity Gravity is the force that –holds us to the Earth –causes a rock to fall towards the ground –causes the Earth to go around the Sun –causes the Sun to be pulled towards the center of the Milky Way galaxy Gravity acts between any two objects even if they are far apart. action at a distance –“ action at a distance ”

15. Modern Universe Is the Sun the center of the Universe?

16. Final Question