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Heliocentric Theory (Edited from Wikipedia)

SUMMARY

Heliocentrism, or heliocentricism, is the astronomical model in which the and revolve around the at the center of the . The word comes from the Greek ( "sun" and kentron "center"). Historically, Heliocentrism was opposed to geocentrism, which placed the Earth at the center. The notion that the Earth revolves around the Sun had been proposed as early as the 3rd century BC by Aristarchus of , but at least in the medieval , Aristarchus's Heliocentrism attracted little attention.

It was not until the 16th century that a geometric of a heliocentric system was presented, by the mathematician, astronomer, and Catholic cleric , leading to the . In the following century, elaborated upon and expanded this model to include elliptical orbits, and presented supporting observations made using a .

HISTORY

To anyone who stands and looks up at the sky, it seems that the Earth stays in one place, while everything in the sky rises in the east and sets in the west once a day. However, with more scrutiny one will observe more complicated movements. The positions at which the Sun and rise change over the course of a year, some planets and stars do not appear at all for many months, and planets sometimes appear to have moved in the reverse direction for a while, relative to the background stars.

As these motions became better understood, more elaborate descriptions were required, the most famous of which was the geocentric Ptolemaic system, which achieved its full expression in the 2nd century. The Ptolemaic system was a sophisticated astronomical system that managed to calculate the positions for the planets to a fair degree of accuracy.

Ptolemy himself, in his , points out that any model for describing the motions of the planets is merely a mathematical device, and since there is no actual way to know which is true, the simplest model that gets the right numbers should be used. However,

1 he rejected the idea of a spinning earth as absurd as he believed it would create huge winds.

The non- of the was proposed by the Pythagorean philosopher (d. 390 BC), who taught that at the center of the Universe was a "central fire", around which the Earth, Sun, Moon and Planets revolved in uniform circular motion. The Pythagorean concept of uniform circular motion remained unchallenged for approximately the next 2000 years, and it was to the Pythagoreans that Copernicus referred to show that the notion of a moving Earth was neither new nor revolutionary.

Muslim astronomers generally accepted the Ptolemaic system and the geocentric model, but by the 10th century texts appeared regularly whose subject matter was doubts concerning . Several Muslim scholars questioned the Earth's apparent immobility and centrality within the universe. Some accepted that the Earth rotates around its axis. Copernicus cited some of the Islamic astronomers whose theories and observations he used in De Revolutionibus .

In the 16th century, Nicolaus Copernicus's De revolutionibus presented a discussion of a heliocentric model of the universe in much the same way as Ptolemy's Almagest had presented his geocentric model in the 2nd century. Copernicus discussed the philosophical implications of his proposed system, elaborated it in geometrical detail, used selected astronomical observations to derive the parameters of his model, and wrote astronomical tables which enabled one to compute the past and future positions of the stars and planets.

In doing so, Copernicus moved Heliocentrism from philosophical speculation to predictive geometrical . In , Copernicus's system did not predict the planets' positions any better than the Ptolemaic system. This theory resolved the issue of planetary retrograde motion by arguing that such motion was only perceived and apparent, rather than real: it was a effect, as an object that one is passing seems to move backwards against the horizon.

This issue was also resolved in the geocentric Tychonic system; the latter, however, while eliminating the major epicycles, retained as a physical reality the irregular back- and-forth motion of the planets, which Kepler characterized as a "pretzel".

2 TYCHO’S RIVAL SYSTEM

Prior to the publication of De Revolutionibus , the most widely accepted system had been proposed by Ptolemy, in which the Earth was the center of the universe and all celestial bodies orbited it. , arguably the most accomplished astronomer of his time, advocated against Copernicus's heliocentric system and for an alternative to the Ptolemaic geocentric system: a geo-heliocentric system in which the five then known planets orbit the sun, while the sun and the moon orbit the earth.

Tycho appreciated the Copernican system, but objected to the idea of a moving Earth on the basis of physics, astronomy, and religion. The of the time (modern Newtonian physics was still a century away) offered no physical explanation for the motion of a massive body like Earth, whereas it could easily explain the motion of heavenly bodies by postulating that they were made of a different sort substance called aether [thanks to Aristotle] that moved naturally .

So Tycho said that the Copernican system "... expertly and completely circumvents all that is superfluous or discordant in the system of Ptolemy. On no point does it offend the principle of mathematics. Yet it ascribes to the Earth, that hulking, lazy body, unfit for motion, a motion as quick as that of the aethereal torches, and a triple motion at that."

Likewise, Tycho took issue with the vast distances to the stars that Aristarchus and Copernicus had assumed in order to explain the lack of any visible parallax. Tycho had measured the apparent sizes of stars (now known to be an illusion), and used to calculate that in order to both have those apparent sizes and be as far away as Heliocentrism required, stars would have to be huge (much larger than the sun; the size of Earth's orbit or larger). Regarding this Tycho wrote, "Deduce these things geometrically if you like, and you will see how many absurdities (not to mention others) accompany this assumption [of the motion of the earth] by inference."

He also cited the Copernican system's "opposition to the authority of Sacred Scripture in more than one place" as a reason why one might wish to reject it, and observed that his own geoheliocentric alternative "offended neither the principles of physics nor Holy Scripture".

The Jesuit (Roman Catholic) astronomers in Rome were at first unreceptive to Tycho's system. However, after the advent of the telescope showed problems with some geocentric models (by demonstrating that circles the sun, for example), the Tychonic system and variations on that system became very popular among geocentrists. Some Jesuit (Roman Catholic) astronomers would continue Tycho's use

3 of physics, stellar astronomy (now with a telescope), and religion to argue against Heliocentrism and for Tycho's system well into the seventeenth century.

RELIGIOUS CONFLICT

The first information about the heliocentric views of Nicolaus Copernicus was circulated in manuscript completed some time before May 1, 1514. Although only in manuscript, Copernicus' ideas were well known among astronomers and others. His ideas contradicted the then-prevailing understanding of the Bible. In the King James Bible First Chronicles 16:30 state that " also shall be stable, that it be not moved." 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."

Nonetheless, in 1533, Johann Albrecht Widmannstetter delivered in Rome a series of lectures outlining Copernicus' theory. The lectures were heard with interest by Pope Clement VII and several Catholic cardinals. On November 1, 1536, Archbishop of Capua Nikolaus von Schönberg wrote a letter to Copernicus from Rome encouraging him to publish a full version of his theory.

However, in 1539, said:

"There is talk of a new astrologer who wants to prove that the earth moves and goes around instead of the sky, the sun, the moon, just as if somebody were moving in a carriage or ship might hold that he was sitting still and at rest while the earth and the trees walked and moved. But that is how things are nowadays: when a man wishes to be clever he must . . . invent something special, and the way he does it must needs be the best! The fool wants to turn the whole art of astronomy upside-down. However, as Holy Scripture tells us, so did Joshua bid the sun to stand still and not the earth."

This was reported in the context of a conversation at the dinner table and not a formal statement of faith.

The work of Copernicus inspired very little debate on whether it might be heretical during the next 60 years. There was an early suggestion among Dominicans that the teaching of Heliocentrism should be banned, but nothing came of it at the time.

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THE

The Galileo affair was a sequence of events, beginning around 1610, culminating with the trial and condemnation of Galileo Galilei by the Roman Catholic in 1633 for his support of heliocentrism.

Galileo began his telescopic observations in the later part of 1609, and by March 1610 was able to publish a small book, The Starry Messenger, relating some discoveries that had not been dreamed of in the philosophy of the time:

1. mountains on the Moon, 2. lesser in orbit around , and 3. the resolution of what had been thought to be very cloudy masses in the sky (nebulae) into collections of stars too faint to see individually without a telescope.

Other observations followed, including the and the existence of sunspots.

Galileo's contributions caused difficulties for theologians and natural philosophers of the time, as they contradicted scientific and philosophical ideas based on those of Aristotle and Ptolemy and closely associated with the Catholic Church. In particular, Galileo's observations of the phases of Venus, which showed it to circle the sun, and the observation of moons orbiting Jupiter, contradicted the geocentric model of Ptolemy and supported the Copernican model advanced by Galileo.

Jesuit astronomers, experts both in Church teachings, , and in , were at first skeptical and hostile to the new ideas; however, within a year or two the availability of good enabled them to repeat the observations. In 1611, Galileo visited the Collegium Romanum in Rome, where the Jesuit astronomers by that time had repeated his observations.

Christoph Grienberger, one of the Jesuit scholars on the faculty, sympathized with Galileo’s theories, but was asked to defend the Aristotelian viewpoint by Claudio Acquaviva, the Father General of the Jesuits. Not all of Galileo's claims were completely accepted: , the most distinguished astronomer of his age, never was reconciled to the idea of mountains on the Moon, and outside the college many still disputed the reality of the observations.

5 In a letter to Kepler of August 1610, Galileo complained that some of the philosophers who opposed his discoveries had refused even to look through a telescope:

My dear Kepler, I wish that we might laugh at the remarkable stupidity of the common herd. What do you have to say about the principal philosophers of this academy who are filled with the stubbornness of an asp and do not want to look at either the planets, the moon or the telescope, even though I have freely and deliberately offered them the opportunity a thousand times? Truly, just as the asp stops its ears, so do these philosophers shut their eyes to the light of truth.

On February 19, 1616, the Inquisition asked a commission of theologians, known as qualifiers, about the propositions of the heliocentric view of the universe.

On February 24 the Qualifiers delivered their unanimous report: the idea that the Sun is stationary is "foolish and absurd in philosophy; and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture"; while the Earth's movement "receives the same judgement in philosophy; and ... in regard to theological truth it is at least erroneous in faith."

At a meeting of the Inquisition on the following day, instructed it to deliver this result to Galileo, and to order him to abandon the Copernican opinions; should Galileo resist the decree, stronger action would be taken. On February 26, Galileo was ordered,

to abstain completely from teaching or defending this doctrine and opinion or from discussing it... to abandon completely... the opinion that the sun stands still at the center of the world and the earth moves, and henceforth not to hold, teach, or defend it in any way whatever, either orally or in writing.

In 1633 (when he was 69 years old), Galileo wrote a book critical of the Ptolomaic model. It was given in the form of a conversation between three men: a Copernican, a witty scholar, and an Aristotelian defender who sounds like an idiot. His book defended heliocentrism, and was immensely popular. The new Pope was convinced that Galileo was mocking him as the Aristotelian. So, the Inquisition investigated him again.

Galileo was interrogated while threatened with physical torture.

The tried Galileo in 1633 and found him "vehemently suspect of ", sentencing him to indefinite imprisonment. Galileo was kept under house arrest until his death in 1642.

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