1. Our solar system

2. The solar system in the 16 th century That is how we think of our solar system

3. And that’s what people thought in the 16 th century.

4. It was natural for the early astronomers to imagine that the earth was at the center of the universe. We see the sun and the moon raising and setting… http://www.youtube.com/watch?v=Mgsf- xTbdpI

5. … and we see the planet moving around the earth http://www.youtube.com/watch?v=46WHS TNZTfghttp://www.youtube.com/watch?v=46WHS TNZTfg

6. When we observe the sky from Earth, the planets appear to move from east to west. Occasionally, the planets will appear to reverse direction--this phenomenon was known as retrograde motion. The astronomers explained this phenomenon by saying that the planet moved along very complicated orbits called epicycles

7. Yes, the planets moved in a very funny manner… but here is an explanation that sounded pretty good, and was so good that was accepted for 1300 years. http://www.youtube.com/watch?v=utH- GHH1FT8&feature=related

8. Claudius Ptolomey Claudius Ptolemy (AD 90 – c.AD 168), was a Greek-Roman citizen who lived in Egypt under Roman rule There is no reason to suppose that he ever lived anywhere else than Alexandria, where he died around AD 168

9. Ptolomey wrote several influential textbooks of astronomy, and even though the geocentric model was not invented by him, but probably postulated as early as the 6 th century BC, and accepted and developed by Plato and Aristotle, he got credit and recognition because he provided a convincing explanation of the apparently complex motion of the planets.PlatoAristotle

10. Not all ancient Greeks agreed with the geocentric model. The Pythagoreans for example (300 BC) believed the Earth to be one of several planets “going around a central fire”. But these philosophers were a minority and probably they were not treated too seriously

11. In the 16 th century, the geocentric model of the solar system was still universally accepted. In particular the church strongly supported the geocentric model because of a passage in the King James Bible (Chronicles 16:30) which states that "the world also shall be stable, that it be not moved." Also, Psalm 104:5 says, "[the Lord] Who laid the foundations of the earth, that it should not be removed for ever." Ecclesiastes 1:5 states that "The sun also ariseth, and the sun goeth down, and hasteth to his place where he arose." …and at the time, the Church took the bible very literally.

12. In the 16 th century, the catholic church, was the power behind the power in half Europe; contradicting the doctrine of the Church had very serious consequences …

14. But the progress of the astronomical observations made Ptolomey’s theories more and more implausible.

15. Copernicus Nicolaus Copernicus (1473 - 1543) was a German astronomer and the first person to formulate a comprehensive heliocentric cosmo logy which replaced the Earth with the sun at the center of the universe. Copernicus' epochal book, De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres), published just before his death in 1543, is often regarded as the starting point of modern astronomy and the beginning of the scientific revolution.De revolutionibus orbium coelestiumastronomyscientific revolution

16. Like many renaissance men, Copernicus was multitalented: he was a mathematician, astronomer, ju rist with a doctorate in law, physician, polyglot, (he was said to spoke perfectly 4 languages), classics scholar, translator, artist, Catholic cleric, (at the time, a necessary requirement to be an academic), governor, diplomat and economis t.

17. The heliocentric model Copernicus became interested in astronomy and published an early description of his "heliocentric" model of the solar system in Commentariolus (1512). In this model, the sun was actually not exactly the center of the solar system, but was slightly offset from the center. As we said, the idea that the Sun was the center of the solar system was not new but Copernicus also worked out his system in full mathematical detail. Even though the mathematics in his description was not any simpler than Ptolemy's, it required fewer basic assumptions. By postulating only the rotation of the Earth, revolution about the sun, and tilt of Earth's rotational axis, Copernicus could explain the observed motion of the planets.

18. Since he still assumed that the orbits of the planets were circular, he had to fumble a bit to make sense of the astronomical observations, but his model was quite an improvement with respect to Ptolomey’s. Unfortunately, out of fear that his ideas might get him into trouble with the church, Copernicus delayed publication of them.

19. However, Copernicus’ ideas circulated, and were at first rejected. The Copernican model appeared to be contrary to common sense and to contradict the Bible! Copernicus theories were not much easier to use than Ptolomey’s and did not produce very accurate predictions of planetary positions Copernicus was aware of this, but he insisted that although his theory was not conclusive, it was more complete and elegant s than his predecessors’. Tycho Brahe arguably the most accomplished astronomer of his time, appreciated the elegance of the Copernican system, but objected to the idea of a moving Earth on the basis of physics, astronomy, and religion. The physics of the time offered no physical explanation for the motion of a massive body like Earth, but could easily explain the motion of heavenly bodies by postulating that they were made of a different sort substance called aether that moved naturally around the Earth.

20. So, Copernicus’ theories were unpublished and not fully believed, and because of that they stayed under the Church’s radar for a while. But during the 17th century, several further discoveries eventually led to the complete acceptance of heliocentrism. In particular, the newly- invented telescope lead Galileo to discover the four large moons of Jupiter (evidence that the solar system contained bodies that did not orbit Earth), the phases of Venus (the first observational evidence for Copernicus' theory) and the rotation of the Sun about a fixed axis as indicated by the apparent annual variation in the motion of sunspots…. And now, let’s talk about Galileo!