1. Origin of Modern Astronomy
Who is Stan Hatfield and Ken Pinzke

2. Key Terms Geocentric Theory - Earth centered Universe
Heliocentric Theory – Sun centered Universe

3. Geocentric Theory
Ancient Greece

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

6. Ptolemaic System
• Ptolemy created a model of the universe that accounted for the movement of the planets.
• Retrograde motion is the apparent westward motion of the planets with respect to the stars.
Retrograde motion of Mars
East
West
Sept.
Aug.
July
June
Dec.
Jan.
Feb.
March
April
May

7. Retrograde Motion

8. The Birth of Modern Astronomy
Copernicus
Argued that the motion of the Sun & planets could be equally described by a Sun centered system.
This model explained the retrograde motion of planets better than the geocentric model.

9. Heliocentric Theory

11. The Birth of Modern Astronomy
Tycho Brahe
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.
 Tycho Brahe
 Johannes Kepler

12. Johannes Kepler - 1609 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.

13. Galileo
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.

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

15. Gravity’s Influence on Orbits
Makes no sense without caption in book

16. 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.

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

18. Final Question
Final Question