The planets themselves must move on smaller rings attached to their respective spheres to match their relatively complex observations in the sky. The outer sphere carries the so-called fixed stars, which are always in fixed positions with each other, but rotate across the sky together. Outside of what the last sphere was, that model never spoke clearly, but it certainly thought it was part of a universe that humans could not observe.
Ptolemy's model created a relatively accurate system for predicting the positions of celestial bodies in the sky. But to accurately predict those positions, Ptolemy had to hypothesize that the moon moved in an orbit that sometimes brought it twice as close to Earth as it did at times. other. Ptolemy had to accept that weakness, but anyway, it was acceptable. This model has been approved by the Catholic church as a picture of the universe in accordance with the Bible, because it has a great advantage of saving quite a lot of space outside the last bridge of the stars. Fixed for heaven and hell.
However, a simpler model was proposed by a Polish pastor by the name of Nicholas Copernicus in 1554. (At first, perhaps for fear of the church being a heresy, Copernicus allowed the model to be circulated. as an anonymous work). His idea was that the sun stood still, while the earth and planets moved in circular orbits around the sun. It took almost a century for this idea to be truly accepted. Two astronomers - a German by the name of Johannes Kepler and an Italian by the name of Galileo Galilei - began to openly support the Copernican theory, although the orbits it predicted did not match the orbits perfectly. observable. And in 1609 a fatal blow struck the Aristotelian - Ptolemy doctrine. In that year, Galileo began observing the sky with his newly invented telescope. When observing Jupiter, Galileo found that there were also some satellites, in other words, moons orbiting it. This implies that not all galaxies necessarily necessarily orbit directly around the earth, as Aristotle and Ptolemy thought. (Of course, it is still possible to believe that the Earth stands still at the center of the universe and Jupiter's moons follow extremely complex orbits that make it feel like it orbit Jupiter. Copernicus's theory is much simpler). At the same time, Kepler improved Copernicus's doctrine by assuming that planets did not move in a circle but in an ellipse. And the predictions now fit perfectly with observation.
For Kepler, elliptical orbits are simply a convenient hypothesis and thus more difficult to accept because ellipses are clearly less complete than circles. When Kepler discovered that it was almost by chance that elliptical orbits were well-suited to the observation, Kepler could not reconcile it with his idea that planets orbiting the sun were due to magnetic forces. This was not until later, in 1867, explaining, when Isaac Newton published his work Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). Perhaps this is the most important physical work ever published. In this work, Newton not only proposed a theory that describes the movement of objects in space and time, but also developed a complex mathematical tool for analyzing those movements. Moreover, Newton also introduced a law of universal gravitation whereby each object in the universe was attracted to another by a stronger force if the two objects were heavier and the closer they were together. It was this force that forced the objects to fall to the ground. (The story goes that, due to the apple hitting the head, Newton inspired the invention of the law of universal gravitation, which was certainly a mere fabrication. what Newton said was just the idea of being appealing to him while sitting in the "contemplative state" and "born of the falling apple". Newton pointed out that according to his law, gravity would make the moon move in elliptical orbits around the earth and planets elliptical orbits around the sun.
The Copernican model abandoned Ptolemy's celestial sphere and, together with them, abandoned the idea that the universe had a natural boundary. Because "fixed stars" do not seem to change their positions except the rotation around the sky due to the earth's rotation around its axis, it is quite natural to assume that the stars are fixed. are celestial bodies like our sun, but much farther away. Based on his theory of gravitation, Newton found that because stars were attracted to each other, they basically did not