Magic vs Physics: Magic: Nature appears mystical. We are simultaneously afraid and mystified by it, but it remains out side the realm of man. The Universe can act arbitrarily. Physics: Nature is understandable. Man is part of nature, not removed from it. Man lives in a rational Universe governed by cause and effect.

Historical Cosmological Models show a steady progression from those based on Magic/Myth to those based on Physics.

Remember these guys:

Aristotle and Plato

Aristotle stands in the Greek philosophical tradition which asserts that nature is understandable. This tradition, opposed to the idea that nature is under the control of capricious (MAGIC) deities which are to be appeased rather than understood, is one of the roots (PHYSICS) of science.

Okay, our task is to now remove the earth from the center of the Universe and come up with something more sensible:

Elements of the Universe at this time (Aristotle):

• Geocentric Cosmology
• Stars and planets on perfect crystalline spheres
• Universe is perfect and Changeless

Problems:

• observed transient phenomena (comets, novae, variable stars) attributed to disturbances in the upper atmosphere of the earth

• the brightness of the planets varied Aristotelian model makes a definite prediction all planets and stars should move in the same direction . But Mars was known at that time to sometimes move in the opposite direction for a brief period of time (this is known as retrograde motion)

• So Ptolemy builds a complicated machine to preserve the geocentric model and account for retrograde motion and explains the brightness variation of the planets (qualitatively but not quantitatively).
  
  
  

• This model stood for 1500 years before anybody dared to modify it.

Cardinal Nicholas of Cusa (15th Century) thought a lot about cosmology (and other stuff) and came up with the following:

• Every direction is relative
• The Universe has its center everywhere
  The above two means there can be no UNIQUE place in the Universe
• The Earth may not be stationary
• Wherever one stood in the Universe, the same pattern of stars would be strewn out before them (homogeneity)

Thus for the first time we see the ideas of relativity, homogeneity and non-uniqueness expressed. However, it may well be that Cusa was influenced by the ancient roman poet Lucretius and his essay On the Nature of the Universe .

The origin of original ideas are difficult to pin down. Often its the marketing that wins out! Our man Copernicus seems to have marketed the non-uniquess idea quite well:

Copernicus embraces the non-uniqueness idea and then asks why should the earth be at the center - lets put the SUN there However, ARISTARCHUS OF SAMOS did think of this idea first.

Copernician Marketing Poster:

The First Textbook (by Clavius) to Incorporate the New Idea (circa 1540):

This is the First Heliocentric Cosmology

The New Idea of the Universe

In 1551 Erasmus Rheinhold (1511-1553) published the Prutenic Tables of planetary positions, which were based on the Copernican model and enjoyed quite a bit of success. meaning that this model had good predictive power.

The most important aspect of Copernicus' work is that it forever changed the place of man in the cosmos; no longer could man legitimately think his significance greater than his fellow creatures; with Copernicus' work, man could now take his place among that which exists all about him, and not of necessity take that premier position which had been assigned immodestly to him by the theologians.

Goethe's Comment on Copernicus: "Of all discoveries and opinions, none may have exerted a greater effect on the human spirit than the doctrine of Copernicus. The world had scarcely become known as round and complete in itself when it was asked to waive the tremendous privilege of being the center of the universe. Never, perhaps, was a greater demand made on mankind - for by this admission so many things vanished in mist and smoke! What became of our Eden, our world of innocence, piety and poetry; the testimony of the senses; the conviction of a poetic - religious faith? No wonder his contemporaries did not wish to let all this go and offered every possible resistance to a doctrine which in its converts authorized and demanded a freedom of view and greatness of thought so far unknown, indeed not even dreamed of."

The Universe according to Copernicus, who had no idea what the stars were in relation to this Universe.

This also gives a natural explanation for the observed retrograde motion that Ptolemy struggled with:

Also this explained the variation in brightness observed for Mars. Copernicus, however, didn't understand how the larger brightness variations observed in Venus could be accounted for.

That is, he did not understand that Venus would have phases:

And now we come to Galileo the Astronomer:

The Telescope an interesting invention.

With his Telescope Galielo Discovered (by 1610 these observations could and were reproduced by others):

• That the moon was non-uniform and had blemishes

• That the sun had spots

• That venus showed phases

• That there were a lot more stars out there than could be seen with the naked eye Why was this an important discovery

• That saturn had something wrong in its appearance.

• That Jupiter had 4 moons in orbit about this (we will work on this explicitly later).
  

  The satellites of Jupiter