The Revolutions of the Celestial Orbs

Consensed Version:

Some will say that the ideas I put here are mad, so I dedicate this work to you, Pope Paul III, so that, as a lover of learning, you may protect it from enemies. The universe is clearly a sphere, as that is the most perfect shape. The earth is also a sphere, for we can see its shape shadowed in eclipses or infer it from the way a ship falls below the horizon. Until now it as been accepted that the earth is the centre of the universe. But why, then, do the planets seem to follow such odd paths through the sky, when it is obvious that their motion must the perfection of a circle? We can tell that the universe is very large, because stars seem always to be at the same angle to the earth, no matter where viewed from. The ancients though the earth must be the centre because all heavy things fall towards centres, an earth is most heavy, and that the earth cannot be in motion for otherwise clouds would drift away as it spun. But if the air of the earth moves too, then clouds will hold their places. I follow ancient Martianus Capella, and think that the beautiful sun is at the centre, followed by the planets on their spheres, in order of the time they take to complete their circuit round it- Mercury, Venus, then the earth with its moon, Mars, Jupiter, saturn and then the fixed sphere of the distant stars. I declare also that the earth varies in the angle of its axis as it goes round the sun, which accounts for the differences of the seasons. There is no clearer way of understanding the apparent motions of the heavenly orbs.

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

  

  Galilean Satellites Let's see if Galileo could have gotten Kepler's Laws?