The Human Side of Science: Edison and Tesla, Watson and Crick, and Other Personal Stories behind Science's Big Ideas (2016)

Chapter 2: Aristotle, Aristarchus, Copernicus, and Galileo Seek to Determine Earth's Place in the Cosmos


Solar system. Used with permission from Eugene Mann.

It is far better to grasp the universe as it really is than to persist in delusion, however satisfying and reassuring.

—Carl Sagan1

To grasp the real significance of the orbits in which planets circulate around the sun, we've got to go way back again.

Turn off your computers, your Internet connection, iPhone, iMacs, iPad, iWatches, iWhatevers, and go outdoors. It would be best to get as far from city lights as possible, on an evening with little moonlight and minimal clouds.

Look up.

What do you see?

Stars, of course.

Nothing new here. People have seen the lights that we call stars in the sky since before history was recorded.

Let's begin our story at about 3000 BCE with a look at the world of the Minoan sailors from Crete. The Minoans dominated trade in the Aegean and Mediterranean Seas. They had sturdy ships that used both oars and sails. Their ships were so good that some speculate that they could have sailed on the ocean, and possibly even ventured as far as the New World. The Minoans had a fabulous civilization for a while, but their culture was cut short by the eruption of the volcano Thea on the island of Santorini sometime between 1500 and 1600 BCE. The resulting tsunami devastated the Minoans, who were subsequently conquered by mainland Greeks. The beauty and sophistication of the Minoan cities and the sudden disappearance of their entire civilization led to a number of fables, including one that identified their region as the lost continent of Atlantis.


Astute sailors had recognized the usefulness of stars in assisting navigation in the dark waters of the Aegean, and farmers had tracked the position of the sun to tell them when to plant and harvest in the appropriate season. But did these stars and constellations of stars have more than utilitarian value?


The Minoan sailors brought more than goods back and forth across the Mediterranean. They learned older ideas about stars and constellations from the Babylonians and Sumerians who lived in the Middle East, brought them across the Mediterranean, and in turn taught them to the Egyptians. Joining stars with lines like a connect-the-dots puzzle yielded interesting figures in the sky. For example, most everyone has seen the three stars in a row that make up the belt of Orion, who was a hunter figure in Babylonian lore. Interestingly, rather than focus on the lights, ancient South American astronomers (Incas) saw patterns in the dark areas of the sky such as the constellation Llama, in which the stars Alpha Centauri and Beta Centauri form its eyes, while dark spaces make up the body. Initially named for things they seemed to resemble, constellations later became associated with gods, and sometimes were actually thought of as being gods. Great significance was especially given to one group of constellations through which the sun and moon traced their narrow path. This plane is called the ecliptic, and it makes a complete 360-degree circle in the sky. The constellations along the ecliptic are called the zodiac constellations. The zodiac formed the basis for astrology, which was thought by many to be influential in determining the actions of people.

Besides the fixed stars, whose positions were always reliable, another group of lights in the sky was observed to move around a lot. The Greeks called these other lights moving lights planets, meaning wanderers. Such planets were eventually named for Roman gods and, in the minds of many people, assumed heavy roles in determining the course of the future. And then there were objects that suddenly appeared and then disappeared. These were called comets. Many believed comets must signal imminent changes in human affairs, unlike the stars and planets, which followed predictable paths. Eventually, interpretation of events in the heavens and their impact on humans fell under the jurisdiction of the priests and astrologers.

The history of star-gazing is fascinating stuff, but let's move on by fast-forwarding many centuries. We need to have another look at the work of one of the intellectual giants we met in the last chapter. Who might it be that would have the intellectual breadth to integrate the best ideas from past civilizations, some from his immediate teacher, some from his colleagues and, in addition, to add some touches of his own?

You got it. Aristotle.

Here is Aristotle's model of the structure of the whole universe:


Aristotle's universe. By Peter Apien, Cosmographia (1524). From Wikimedia Commons, user Fastfission~commonswiki.

·        Earth is a sphere, located at the very center of the entire universe.

·        The moon, the sun, and the planets are all arranged on larger crystalline spheres surrounding Earth (around fifty of them).

·        These spheres are made of a perfect material, called æther, and rotate around the earth at uniform speeds.

·        The outermost of these spheres houses the fixed stars, and its rotation is caused by the “Prime Mover.”

(Aristotle is vague about the Prime Mover's details.)

Since the earth is at its center, Aristotle's model as well as other similar ones is called a geocentric model.


Aristotle had so many ideas about such a wide variety of topics that he was a big target for disagreement about the validity of his concepts. A later member of his Peripatetic School, Aristarchus (310 BCE–230 BCE), observed the moon carefully and used the mathematics of trigonometry to estimate the size of the sun.


Aristarchus (310 BCE–230 BCE). From Wikimedia Commons, user Christian1985.

According to Aristarchus's measurements and calculations, the sun was substantially larger than the earth, so he thought it made more sense for the smaller earth to orbit the larger sun. Aristarchus's original work didn't survive, so we have only comments about his theory from Archimedes, twenty-five years his junior:

His hypotheses are that the fixed stars and the Sun remain unmoved, that the Earth revolves about the Sun on the circumference of a circle, the Sun lying in the middle of the Floor.2

This model places the sun at the universe's center and so is referred to as a heliocentric model.

Since Aristarchus and Aristotle didn't overlap time-wise, they never had direct interchange about their differences. If a poll had been taken, Aristotle probably would have prevailed, but this was way before physical evidence became science's determining factor. Nevertheless, observations continued, and all astronomical data became more accurate. New information necessitated changes in Aristotle's model, especially because astrological predictions were often mistaken, and these errors were attributed to faulty data about planetary positions.


Ptolemy (90 CE–168 CE). From Wikimedia Commons, user Ineuw

Claudius Ptolemy (90 CE–168 CE) systematized, clarified, and augmented Aristotle's model in his work titled Almagest, published in 150 CE. Ptolemy was probably ethnically Greek, lived in Alexandria, Egypt, as a Roman citizen, and wrote in Greek. The Almagest included a star catalog that listed forty-eight constellations and Handy Tables that tabulated all the data needed to compute the positions of the sun, moon, and planets; the rising and setting of the stars; and eclipses of the sun and moon. Ptolemy's model was geocentric. It contained a series of nested spheres quite similar to Aristotle's. The major difference between Ptolemy's and Aristotle's models was that in Ptolemy's, Earth was displaced slightly from the center (called eccentric), and planetary orbits were circles whose centers were situated on the larger circles that orbited the earth. These are called epicycles. This variation was required to account for the occasional counterintuitive west-to-east motion of planets (called retrograde), which appeared to violate the normal east-to-west motion of heavenly bodies.


Epicycles. From Wikimedia Commons, user Hikin1987.

Ptolemy's Almagest was preserved in Arabic manuscripts. It was studied extensively over several hundred years after the collapse of the Western Roman civilization (400s CE). During the Middle Ages (474 CE–1500 CE), astronomy took a backseat to the culture's more pressing political and religious concerns, so Ptolemy's work stood supreme, since few changes were proposed to anything astronomical.


During the twelfth and thirteenth centuries, as the intellectual reawakening of the Renaissance began, interest in philosophy became much stronger. Aristotle's ideas were still significant but were accessible only through commentaries on translations. Lecture notes (not finished manuscripts) originally written in Greek had been translated into Syriac and Arabic, and were commented upon by the Persian philosopher Avicenna (Ibn Sina) and the Andalusian philosopher Averroes (Ibn Rushd). They each attempted to reconcile Aristotle's philosophy with Islamic teachings. The Syriac/Arabic translations were then retranslated into Latin and Hebrew, and the Spanish Sephardic Jewish philosopher Moses Maimonides (Moshe ben Maimon) commented on their relationship to Judaic teachings. As you might imagine, Latin translations of the work of Islamic and Judaic philosophers and comparisons to their religion's teaching led to much confusion and contention among Westerner Europeans. The Catholic theologians were particularly concerned about whether conflicts between Catholic teachings and Aristotelean ideas were the result of misinterpretations or mistranslations.


Greek manuscripts of Aristotle's lecture notes were discovered. The excellent translator William of Moerbeke was sent by the Dominican theologian Albertus Magnus to Byzantium (now Istanbul) to translate them. Because of language similarities, translation from Greek directly to Latin generated far fewer translation errors than the multiple translations into the structurally dissimilar Syriac/Arabic, and cleaner translations were thus possible. Once the translations were complete, another student of Albertus Magnus, Thomas Aquinas, set out on an extremely ambitious project: to reconcile Aristotle's philosophical works with Catholic teaching.

Thomas Aquinas was remarkably successful, elevating much of Aristotle's thought almost to a par with scripture. Along the way, this included Aristotle's ideas about the solar system, as updated by Ptolemy. Thus, we arrive at 1500 CE with Aristotle's astronomy, at the heart of Catholic teaching.


Next, the Polish astronomer Nicolaus Copernicus (1473–1543) rediscovered Aristarchus's work, then made measurements of his own that convinced him that the sun is the center of the universe, with all planetary spheres and the earth rotating about the sun.


Nicolaus Copernicus (1473–1543). From Wikimedia Commons, user Ineuw.

His ideas, released initially only in partial form, were not well received at first by Protestant theologians, and then by Catholic ones. This was because they didn't fit Ptolemy's model, which, thanks to Thomas Aquinas's synthesis, had (almost) the force of scripture. Hoping to avoid controversy, Copernicus delayed publication of his complete work until he was on his deathbed.



Tycho Brahe (1546–1601). From Wikimedia Commons, user Szajci.

Tycho Brahe was a larger-than-life fellow. He was born in Denmark and lived from 1546 to 1601. His parents had promised to give one of their male children to Tycho's uncle Jørgen and aunt Inger, who were childless, and so he was raised by his uncle and aunt from the age of two. They were quite wealthy and made sure young Tycho had a first-class education. Although Uncle Jørgen wanted Tycho to study law, his initial studies at the University of Copenhagen were quite general and included astronomy. Tycho witnessed an eclipse of the sun when he was fourteen, and it impressed him mightily. At age twenty, Tycho fought a duel with a cousin after a disagreement over a mathematical formula. The duel took place in the dark, and the bridge of Tycho's nose was sliced off. He wore a prosthetic nose made of brass for the rest of his life.3

In 1565, Denmark's King Frederick II had a disaster that greatly influenced Tycho's development. The king was thrown off his horse into a river. Jørgen jumped into the water and saved the king from drowning. Unfortunately, Uncle Jørgen contracted pneumonia and died. Several years later, Tycho's real father also died. With help from another uncle, Steen Bille, Tycho built an observatory. After noting the sudden appearance of a new star in the constellation Cassiopeia, which he called a nova (it was actually a supernova), Tycho realized the crucial importance of accurate measurements. This impelled him to make astronomy his life's work. Realizing the existence of a new star contradicted Aristotle's view of the heavens as unchanging, Tycho began writing and touring to discuss the deficiencies of the old ideas. King Frederick II recognized Tycho's talents and gave him the island of Hven to build an observatory. This observatory was called Uraniborg and was completed before Tycho turned thirty. Uraniborg featured the world's largest and most precise sextant and was supported by the king with 5 percent of Denmark's budget. Tycho Brahe produced the best astronomical data of his time, both in accuracy and amount. He was known as the last and best naked-eye (non-telescopic) astronomer.4

His conception of the universe was a curious hybrid of geocentrism and heliocentrism. As he saw it, all planets except the earth orbited the sun; the sun, the moon, and fixed stars orbited the earth just as Aristotle had thought.


Tycho fell in love with Kirsten Hansen, daughter of a Lutheran minister. Kirsten was a commoner, and Tycho a nobleman, so their marriage was of the common-law variety, and their children could not inherit Tycho's land holdings.

Because of his land grant from the king, Tycho's neighbors on the island of Hven were required to pay him rent. He would go after them legally to collect, earning their ill will. Tycho was known to keep a pet elk that liked to attend parties and drink beer.5 When Frederick II died, his son became the new king, Christian IV. Christian summoned Brahe to discuss his budgetary support, but Brahe put him off for months, pleading that he was too busy. When Christian cut off Brahe's funding, Brahe traveled to Prague to become the royal astronomer for the Holy Roman Emperor Rudolf II. Some suggest that the new king's displeasure might have been related to a possible affair between Tycho and the queen, but there is little evidence of that.

Brahe was difficult to work for and went through many assistants, with the last one being the most interesting: Johannes Kepler.


In Tycho's family tree were cousins named Rosencrantz and Guildenstern, whose names show up in Shakespeare's Hamlet. Also, when James VI of Scotland traveled to Denmark in 1590 to collect his bride, Anne of Denmark, a storm forced his party to spend some time as Tycho's guest on Hven. James VI succeeded Queen Elizabeth of England as James I in 1603 and became Shakespeare's patron.


Johannes Kepler (1571–1630) was a German mathematician, astronomer, and astrologer. As a child, he witnessed a lunar eclipse and saw a comet, both of which impressed him greatly and inspired an abiding love for astronomy. His family fortune was in decline, so he helped make ends meet by casting horoscopes while still in school at the University of Tubingen. Although he was personally skeptical about much of astrology, he practiced it with some disclaimers. As a bright child of poor parents, he successfully passed through the school system, ending up at the University of Tubingen. It was at Tubingen that he became convinced of the reality of the heliocentric Copernican system. Only months before graduation, he was instead sent to be a teacher at a seminary school in Graz, Austria. While teaching, he had an epiphany about planetary orbits. He became convinced that if the Platonic solids were nested within each other, and spheres inscribed and circumscribed each solid, the spheres would describe exactly the orbital radius of each of the six known planets.


Kepler's solids. By Johannes Kepler (1571–1630), Mysterium Cosmographicum (1596). From Wikimedia Commons, user Hellisp.

As long as the solids were placed in the order: octahedron, icosahedron, dodecahedron, tetrahedron, cube, the spheres would describe the planetary orbits closely but not precisely within the accuracy of current measurements. Kepler published this idea in Mysterium Cosmographicum (The Cosmic Mystery). From his viewpoint, Kepler thought he had deduced God's geometrical plan for the solar system. His work was criticized by Tycho, who had much more accurate data on planetary orbits than was available to Kepler. He corresponded with Tycho on this. After more letters and breakdowns in negotiations, Kepler finally came to work as Tycho's assistant in January 1600. Although their relationship was stormy, Tycho began to trust Kepler, gave him access to more data, and introduced him to Rudolf II, for whom he was compiling astronomical data to be issued as the Rudolfine Tables (star catalogs and planetary orbital data).

Suddenly, in late 1601, Tycho died under mysterious circumstances a few days after a heavy drinking session. Soon after his death, his heirs sued Kepler to get Tycho's data for their own. But delaying tactics by Kepler allowed him to hang onto the data he needed. Kepler became the new Imperial Mathematician and advisor to Rudolf II. Details of the orbit of Mars in particular convinced Kepler that his nested-solids scheme was insufficient. Looking for another way to solve the orbit problem, Kepler tried various ovoid-shaped orbits without success and finally used well-defined elliptical orbits, which worked beautifully. Kepler abandoned circular orbits and substituted ellipses because circles were inaccurate by eight minutes of arc in Tycho's accurate measurements of Mars's orbit. Kepler knew that Tycho's data was so accurate that it must all be matched precisely by whatever mathematical form the orbits took.

Now, because they could not be disregarded, these eight minutes alone will lead us along a path to the reform of the whole of Astronomy.6

Three hundred years after his death, Tycho's body was exhumed because of suspicion about his cause of death, and mustache hairs were found to contain mercury, but not enough to justify speculation about the possibility of mercury poisoning.


Galileo Galilei (1564–1642) was born in Pisa, Italy. His father was an accomplished lutenist and musical theorist, and he contributed to the theory of musical dissonance. Money was tight, so Galileo was encouraged to study medicine. While at the University of Pisa, Galileo noticed that chandeliers that swung because of air currents seemed to have the same period of oscillation (time to complete one cycle) whether the swing was wide or narrow. He timed the swings by his pulse. Although he had been purposely kept from studying mathematics, he finally convinced his reluctant father to allow him to study natural philosophy. After inventing the thermoscope (a forerunner of the thermometer) and a hydrostatic balance (an improvement on Archimedes's eureka moment because it was more accurate), his ideas became noticed, and he was given a teaching position first at the University of Pisa, and then later at the University of Padua.


Galileo Galilei (1564–1642). By Caravaggio (1571–1610). From Wikipedia Commons, user Sir Gawain.

While at Padua, a former student of Galileo's wrote him about an invention he had seen in the Netherlands. Hans Lippershey had fitted two glass lenses into a tube, and when you looked through it, distant objects appeared closer. This was called a spyglass. It magnified images by a factor of three. Galileo was quite interested and had his instrument maker, Marcantonio Mazzoletti, make a better one, which magnified eight times. He sold this spyglass to the Venetian Senate, so it could be used to see who was entering the harbor. The Senate awarded Galileo with a lifetime faculty tenure at the University of Padua. Next, Galileo commissioned Mazzoletti to make a twenty-power model, which Greek theologian Giovanni Demisiani called a telescope. Galileo pointed it skyward. He found things never before seen with the naked eye: craters on the moon, spots on the sun, and satellites orbiting around Jupiter. Immediately, he noted the disagreement of these observations with the ideas of Aristotle, whose theory said heavenly bodies are perfect and unchangeable, and everything orbits the earth.

Another difference between Galileo's and Aristotle's ideas had to do with Aristotle's assertion that heavy bodies fall faster than light ones. Some have suggested that Galileo dropped heavy and light bodies from the Leaning Tower of Pisa in the presence of various authorities. When the bodies landed at their feet simultaneously the authorities were forced to choose between the written words of Aristotle and the evidence of their own senses, although there is no historical evidence to support this actual demonstration.


Galileo and the Leaning Tower of Pisa. Used with permission from Sidney Harris.


In 1610, Kepler requested a telescope, but Galileo told him he had no extras and was too busy to even discuss it. A little competitive drive, there?7

Galileo carried on a dispute with the Jesuit priest Orazio Grassi that began about the nature of comets but spilled over into disagreement about the nature of science in general. The quarrel was carried on using pseudonyms, but the identities of the combatants became known. The papers included insulting comments and, as a result, made numerous enemies on both sides.

Galileo also had a dispute with the Jesuit priest Christoph Scheiner regarding sunspots. The controversy took nasty turns with both combatants accusing the other of plagiarism.

Further, Galileo wrote in Italian, the language of the common people, rather than Latin, the usual academic language, so his papers enjoyed wider distribution and attention than those of his academic colleagues.

The relationship between the Roman Catholic Church and science was becoming ever more uneasy. The Catholic Church's Inquisition to root out heretics and blasphemers was extremely powerful. The Italian scientist/mystic Giordano Bruno was burned at the stake for wide-ranging heresy, including some scientific ideas in 1600. Galileo's support for the heliocentric theory of Copernicus placed him under suspicion by the Inquisition, whose members wanted Galileo to state publicly that his theories about a sun-centered universe with imperfect celestial bodies were merely mathematical conveniences and not representative of reality.


Pope Urban VIII (1568–1644). By Caravaggio (1571–1610). From Wikimedia Commons, user Sir Gawain.

But Galileo had an ace up his sleeve. The new pope, Urban VIII, was Maffeo Barberini, whom Galileo had tutored as a youth. The pope requested that Galileo explain both sides of the geocentric/heliocentric controversy and include the pope's own views prominently. Galileo obliged in his famous work Dialogue concerning the Two Chief World Systems.8 In it, he portrays a discussion between fictitious characters, with the official Catholic position being argued (ineffectively) by a character named Simplicio. This name may have honored a similar character in Aristotle's work, the philosopher Simplicius, but it is disturbingly close to the Italian word for simpleton. Galileo's enemies and those involved in court intrigue and problems of state convinced the pope that he needed to show strength, so Galileo had to be silenced. Galileo was convicted of being “vehemently suspect of heresy” and was sentenced to imprisonment. Even as he was being sentenced, Galileo was still rebellious. Supposedly, he muttered, “Eppur si muove,” (“and yet, it moves”). The prison term was commuted to house arrest, so Galileo was unable to travel for the last nine years of his life.9

Bonus Material: Tycho/Galileo Internet interview. See To Dig Deeper for details.

The uneasy science/religion relationship eventually turned into a divorce, with science's final test becoming the existence of physical evidence, while the Church demanded faith regardless of physical evidence. This development is often referred to as the Scientific Revolution. Galileo certainly wasn't single-handedly responsible for this giant change, but he did a lot to install mathematics as the language of science and experimental evidence as the chief decider.

In the next chapter, the role of experimental evidence in science is so strong it is almost taken for granted.