Galileo experimented with pendulums, with balls rolling down inclined planes, with light and mirrors, with falling bodies, and many other objects. Aristotle had said that heavy objects fall faster than lighter ones. Galileo argued, and showed in experiments, that if a heavy and light object were dropped together, even from a great height, both would hit the ground at practically the same time. What little difference there was could easily be accounted for by the resistance of the air.
In the course of his experiments, Galileo discovered laws that invariably described the behavior of physical objects. The most far-reaching of these is the law of inertia. The inertia of a body is that property of the body that resists any change of motion. It was familiar to all people then as it is to us now that if a body is at rest it tends to remain at rest, and requires some outside influence to start it in motion. Rest was thus regarded as the natural state of matter. Galileo showed, however, that rest was no more natural than motion. If an object is slid along a rough horizontal floor, it soon comes to rest, because friction between it and the floor acts as a retarding force. However, if the floor and object are both highly polished, the body, given the same initial speed, will slide farther before coming to a rest. Galileo noted that the less the retarding force, the less the body's tendency to slow down, and he reasoned that if all resisting effects could be removed the body would continue in a steady state of motion indefinitely. In fact, he argued, not only is a force required to start and object moving from rest, but a force is also required to slow down, stop, speed up, or change the direction of a moving object.
Galileo also studied the way bodies accelerated, that is, changed their speed, as they fell freely, or rolled down inclined planes. He found that such bodies accelerate uniformly, at a rate of 9.8 meters per second per second. This acceleration was irrespective of the type or size of the body.
In answer to the common objection that objects could not remain on the Earth if it were in motion, Galileo noted that if a stone is dropped from the masthead of a moving ship it does not fall behind the ship and land in the water beyond its stern, but rather lands at the foot of the mast, for the stone already has a forward inertia gained from its common motion with the shop before it is dropped. In an analogous way, objects on the Earth would not be swept off and left behind if the Earth were moving, for they share the Earth's forward motion.
It is not certain when the principle was first conceived of combining two or more pieces of glass to produce an instrument that enlarged distant objects, making them appear nearer. Claims for the discovery exist as early as the time of Roger Bacon in the 13th century. At any rate, the first telescopes that attracted much notice were made by the Dutch spectacle-maker Hans Lippershey in 1608. Galileo heard of the discovery in 1609, and without ever having seen an assembled telescope, he constructed one of his own.
Galileo found that many stars too faint to be seen with the naked eye became visible with his telescope. In particular, he found that some nebulous blurs resolved into many stars, and that the Milky Way was made up of multitudes of individual stars. He found that Jupiter had four satellites or moons revolving about it with periods ranging from just under 2 days to about 17 days.
This discovery was particularly important because it showed that there could be centers of motion that in turn were in motion. It had been argued that if the Earth were in motion the Moon would be left behind, because it could hardly keep up with a rapidly moving planet. Yet here were Jupiter's satellites doing exactly that.
Another important telescopic discovery that strongly
supported the Copernican view was the fact that Venus goes through phases
like the Moon. In the Ptolemaic system, Venus is always closer to the Earth
than is the Sun, and thus, because Venus never has more than about 45
elongation, it would never be able to turn its fully illuminated surface
to our view- it would always appear as a crescent. Galileo, however, saw
that Venus went through both crescent and gibbous phases, and concluded
that it must travel around the Sun, passing at times behind and beyond
it, rather than revolving directly around the Earth. Subsequent observations
by other astronomers showed that Mercury also goes through all theses phases.
Galileo also made observations of the Moon. He saw craters, mountain ranges, valleys, and flat dark areas that he guessed might be water. not only did these discoveries show that the heavenly bodies, regarded as perfect, smooth, and incorruptible, do indeed have irregularities, as does the Earth, but they showed the Moon to be not so dissimilar to the Earth, which suggested that the Earth, too, could belong to the realm of celestial bodies.
Galileo also found that Saturn seemed to appear strange, although his telescope was not good enough to show the true nature of the planet. It was not until 1655 that Huygens described the ring system that exists about Saturn.
One of Galileo's most disturbing observations, to his contemporaries, was of spots on the Sun, showing that this body also had "blemishes". Sunspots are now known to be large, comparatively cool areas on the Sun that appear dark because of their contrast with the brighter and hotter solar surface. Sunspots are temporary, lasting usually only a few weeks to a few months. Large sunspots actually had been observed before, with the unaided eye, but were explained by western theologians as either something in the Earth's atmosphere or as planets between the Earth and the Sun silhouetting themselves against the Sun's disk in the sky. In fact, some of Galileo's critics attempted to explain the spots as satellites revolving about the Sun.
Galileo observed the spots to move, day by day, across the disk of the Sun. He also noted that they moved most rapidly when near the center of the Sun's disk and increasingly slowly as they approached the limb (the Sun's limb is its apparent edge as we see it in the sky). Often, after about two weeks, the same spots would reappear on the opposite limb, and move slowly at first, them more rapidly towards the center of the disk. Galileo explained that the spots must either be on the surface of the Sun or very close to it and that they were carried around the Sun by its own rotation. Their variable speed, he showed, is an effect of foreshortening; when near the center of the Sun's disk they are being carried directly across our line of sight, but near the limb most of their motion is either toward or away from us. He determined the Sun's period of rotation to be a little under a month.
When Galileo wrote The Letters of Sunspots, reporting on his finding the imperfections of the Sun, he declared his belief in the Copernican system. This announcement by Galileo began an uproar which would cause Galileo, and society in general, much grief. One factor contributing to the opposition engendered by the letters was that Galileo wrote them in Italian. Galileo choose to write in the language of the people of his country because he was convinced that people other than scholars could understand his arguments and his evidence that the Copernican system was correct. Unfortunately, one of the disagreements between the Catholic church and the Protestant movement was over the use of vernacular languages in place of Latin.
Primarily because of this controversy, the Catholic church declared in 1616 that the Copernican doctrine was "false and absurd" and a proclamation was issued stating that Galileo was forbidden to "hold or defend" the odious hypothesis.
Why did the church make such a strong statement? We must realize that they considered the salvation of the individual of paramount importance; more important than answering the question of what is the best world theory. They feared that the idea of a non-geocentric world might confuse people as to the supremacy of humankind in God's plan and therefore threaten the salvation of those people.
The Catholic church became particularly involved in Galileo's case for at least three reasons. First, Galileo sought to be a faithful Catholic all of his life. Second, the church was a hierarchical and authoritarian church and it had much more authority in Galileo's time than it has today. Third, the church was still recoiling from the Reformation and there was a tendency to overreact to anything that could be seen as heresy.
The book appeared in 1632 under the title Dialog on the Two Great World Systems. The book is written in Italian to reach a large audience and is a magnificent and unanswerable argument for the Copernican system. It is in the form of a conversation, lasting four days, among three philosophers: Salviati, the most brilliant; Sagredo, who is usually quick to see the truth of Salviati's arguments; and Simplicio, an Aristotelian philosopher who brings up all the usual objections to the Copernican system, which Salviati promptly shows to be absurd.
It is pointed out in the preface to the book that the arguments to follow are merely a mathematical fantasy, and that divine knowledge assures up of the immobility of the Earth. This was thinly cloaked irony, however, and Galileo's enemies quickly built a case against him. He was called before the Holy Inquisition on the charge of believing and holding doctrines that are false and contrary to Divine Scriptures. Galileo was forced to plead guilty and deny his own beliefs. His life sentence was commuted to confinement in his own home for the last ten years of his life.
Much has been written about the case of Galileo. What is important to realize is that the case was not a simple one. The Copernican model was not the only model that was capable of describing the world and the Ptolemaic model did indeed have some advantages over Copernicus' model. Remember that the work of Kepler was not well known and that Galileo's findings were new and controversial. In addition, Galileo was not a diplomatic person. He wrote in the vernacular language so that theoretical discussions which in the past had taken place among scholars were now exposed for all to see.
On the other hand, church leaders saw these new ideas as a threat both to their own authority and to the authority of the Holy Scripture. By silencing Galileo, they sought to quell these threatening ideas they regarded as false. Also, there is evidence that part of Galileo's troubles stemmed from a grudge against him by some church authorities.
Whatever the true reasons and motives, the trial of Galileo made an indelible mark on the interrelations between science and religion. Until this time in the western world, science and religion were intimately related, as they were in most of the other cultures in the world. Only the theologians had the time and education to pursue a scholarly existence, and indeed one of the earliest functions of the monasteries was to provide copies of ancient books for study and dissemination by the church. Study in the sciences was done to answer questions proposed by the requirements of the church, and technical advancements were frequently propelled by the church's needs.
All of this changed with the trial of Galileo.
In one quick move, the church severed its close ties with science and changed
its stand by 180.
From then on, the church assumed a cautious stance on science, and frequently
opposed scientific research as being against the will of God. This does
not mean that the church has refrained from pursing scientific research.
Indeed, throughout the centuries some of the major advances have continued
to be made by scientists who were also theologians. However, as often as
not religious beliefs have refuted scientific findings based solely on
the fact that the findings contradict those beliefs. This is a sad legacy,
but one which still exists today.
Last Updated: August 28, 1997
Comments to: D-Suson@tamuk.edu