you may enjoy the Ptolemaic System Simulator [2].
The heliocentric model of Copernicus, Galilei and Kepler
Nicolaus Copernicus (1473 - 1543) had a number of well-founded objections to the Ptolemaic model. Among objections concerning its complexity, he pointed to the enormous centripetal force that would be needed to keep the 24-hour spinning fixed star sphere together. These concerns led him to devise a heliocentric model with perfectly circular planet trajectories around the central sun with the sun however positioned just a little bit off-center. Gravity as a universal principle was still unthought of at that time. The nature of the force that constrained the planets to their orbits and what powers pushed them along on their trajectories were unknown to him. He imagined angelic beings charged with these heavenly tasks.
In 1543, shortly before his death, Copernicus published his life work - "De Revolutionibus Orbium Coelestium" [3]. Dying on publication was a wise action seen in the light of the views of his bread and butter, the church, and also because of the wrath of the Inquisition. Remarkable is its foreword, written by the Lutheran theologian Andreas Osiander. Osiander wrote that this new hypothesis should be considered as a less complex mathematical method, compared to Ptolemaic calculations, to calculate the planetary positions, but that it should not be considered as representing reality. This is reminiscent of the situation in which quantum physics is still held at the present day. Quantum mechanics makes extremely accurate predictions, but most physicists prefer to ignore its actual meaning, 'Shut up and calculate'. The message was anyway that established science, and especially the church, could still avoid the real message of Copernicus and keep their own beliefs intact.
Incidentally, his heliocentric model had quite a few serious shortcomings. Its predictive accuracy was even inferior to that of the Ptolemaic geocentric model. In addition, one was not relieved of those unwieldy epicycles. In fact, eight extra epicycles had to be added by the religious canon Copernicus, because he couldn't say goodbye to the divine perfectly circular motions in the heavens.
Copernicus is nowadays an exuberantly honored person in Poland, considering the post stamps, taxi companies, T-shirts and cafeterias, all bearing his name. You cannot avoid it when visiting Torún, his hometown, or Olsztyn, the town where he worked as canon. A salient detail is, that in the days of the German-speaking and Latin-writing Copernicus, Poland did not even exist as a nation.
The Italian scholar and skilled experimenter Galileo Galilei (1564-1642) bought a Dutch spyglass on the market and improved it considerably. A spyglass presenting an upright image is called a 'Dutch spyglass'. This type of spyglass was invented simultaneously in 1609 by two lens grinders and polishers, Sacharias Jansen and Hans Lipperhey, both citizens of the Dutch city of Middelburg. Lipperhey was the first one applying for a patent for his invention 'voor de buyse waarmede men verre kan sien'('a tube for seeing things far away as if they were nearby'). Lipperhey's request for a patent was rejected however, because 'just everyone should be able to fix two pieces of glass behind each other'. Instead of its intended use, the early detection of ships at sea, Galileo looked straight up with it and discovered four moons circling around Jupiter.
Figure 2.3: Dialogo di Galileo Galilei Lincio
On the basis of his observation of the moons of Jupiter and of the moonlike phases of Venus, Galileo concluded that it was the sun that should definitely be at the centre of the solar system and that Copernicus had it right. He published his "Dialogo" in 1632 for which he had managed to obtain the church's imprimatur by stating in the preface, just like Copernicus, that its message was purely hypothetical. The book contains four dialogues conducted between three persons of which one, Simplicio, is the stupid fool. The arguments for the earth in the centre are expressed by him. Simplicio's arguments were easily recognizable as the same arguments that the then pope Urban VIII expressed. Although the pope was, until then, on friendly terms with Galilei, both being from the same region in Italy, and had protected Galilei thus far against the alarming attention of the Inquisition, the pope in his indignation then unleashed the Inquisition on Galilei. In order to protect his life and limbs Galilei had to withdraw his hypothesis publicly and thus kept his life but was under house arrest for the rest of his life. In 1992, only after 450 years, the church of Rome offered her apologies. The Vatican even considered placing a bust of Galilei in its gardens, but to date this has not been realized.
Galilei was well acquainted with the publication of Johannes Kepler (1571-1630) - "Astronomia Nova" - which appeared in 1609. Kepler had studied the observations of Tycho Brahe intensively, which were the most accurate registered measurements given the technology of the time. Kepler discovered, by his study of Tycho's tables, that the orbits of the planets were not God's perfect circles, but that they were elliptical. He discovered also that the planets did not move at uniform velocities along their trajectories. Which is Kepler's first law.
Figure 2.4: Kepler's second law.
Kepler's second law, the law of equal areas, is the best known by far. See figure 2.4. When a planet moves from A to B in the same time as from C to D, the grey marked areas in figure 2.4 are equally large.
Kepler's third law is also called the harmonic law [4]. The square of the orbital time of a planet is proportional to the third power of average distance from the sun.
Kepler formulated a mathematical equation, now called the Kepler's equation [5], with which the deviation of a fictitious circular trajectory of the planet in its orbit around the sun can be calculated.
Kepler's three laws [6] together with his equation formed the basis of Isaac Newton's law of gravitation in 1687.
The publications of Copernicus, Kepler and Galilei marked the end of an era of more than 1400 years during which the geocentric Ptolemaic model had been supreme. Until that moment, almost every respected scholar had committed himself to the Ptolemaic model, at least publicly. These conservative scholars, stubbornly holding on to their trusted old views, even refused to look through Galilei's telescope because they knew 'how the world was' and called it an instrument inspired by the devil which only showed you hallucinatory misleading images. This is cognitive dissonance, a common human behavior, avoiding world view disturbing facts. Proclaiming in those days that the earth was not at the centre of the cosmos was at the very least a bad career choice and could even be risky for your neck.
Sir Isaac Newton (1643 - 1727)
In the first two thirds of the twentieth century the physics taught in high school, and for an important part of that century also at universities, was still 100% Newtonian physics, also known as Newtonian mechanics. This foundation of Newton mechanics on which physics education nowadays is still resting for a large part is a great and rightful compliment to its original creator, Sir Isaac Newton [7].
In favorable contrast
