1. Universal Gravitation
Nature and Nature's laws lay hid in night; God said, Let Newton be! and all was light.
- Alexander Pope

2. Ancient Times
The oldest recorded astronomical observations were from around 4,000 BC (Egypt, Central America).

3. Aristarchus of Samos 310-230 BCE
Aristarchus proposed a heliocentric model.
Calculated ratio of distances between Earth, Moon, and Sun.

4. Eratosthenes 276 BCE – 194 BCE
Determined Earth's circumference to within 5 percent of the accepted value.

5. Claudius Ptolemy d. 180 CE Earth-centric system.
Could accurately predict astronomical events with his model.
Explained retrograde motion.

6. Claudius Ptolemy
Ptolemy’s theories last for 1,400 years!

7. Nicolaus Copernicus (1473 to 1543)
There is no one center in the universe.
The Earth's center is not the center of the universe.
The center of the universe is near the sun.
The distance from the Earth to the sun is imperceptible compared with the distance to the stars.
The rotation of the Earth accounts for the apparent daily rotation of the stars.
The apparent annual cycle of movements of the sun is caused by the Earth revolving round it.
The apparent retrograde motion of the planets is caused by the motion of the Earth from which one observes.

8. Galileo Galilei ( )
Using a telescope he made, Galileo observed:
Moons of Jupiter.
Phases of Venus.
His findings supported a Copernican model.
He spent the end of his life under “house arrest” for his beliefs.

9. Johannes Kepler ( )
Deeply religious, Kepler thought God made the Universe according to a mathematical plan.
Attempted to relate structure to nested geometric solids.

10. Kepler’s Three Laws 1st Law: Path of planets are elliptical.
Planet sweeps out equal area in a given time.
r3/T2 = k for objects orbiting a common center.

11. Sir Isaac Newton ( )
If I have been able to see further, it was only because I stood on the shoulders of giants Letter to Robert Hooke

12. Sir Isaac Newton ( )
The fact orbits are constant must be due to a force keeping planets in orbit.
The same force that makes an apple fall to the ground, could be acting on planets!

13. Bibliography http://www.astromax.org/astrocourse/history.htm
geodesy/geo02_histr.html