Stonehenge as it remains. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
Stonehenge as it remains. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
Sections
Astronomy is often cited as the oldest, empirical (i.e., based on observation), exact science.
One can quibble, but there really is no other candidate if one regards mathematics as an abstract science that is only applied in the empirical world.
This all may be just point of view.
How old is astronomy as an exact science?
Well there are moon-shaped cut marks on bones in groupings of order 30 from as long ago as 36,000 BCE that seem to be counts of days during a lunar month (No-xxiv).
In many societies, the start of the lunar month is the actual observation of the first crescent even though that is obviously dependent on weather.
In ancient times, astronomy and meteorology were not clearly separated---both are about sky phenomena. Stars are much farther away than clouds, but that is not obvious by-eye observation.
Even from its earliest days, some observers were probably interested in astronomy for its own sake. They wanted to know where things in the sky were and when they would appear.
But astronomy for astronomy's sake was probably not important for most early people.
There is no reason to doubt that prehistoric and early historic (i.e., literate) people saw celestial phenomena as manifestations of the divine.
In many cases, perhaps most, they probably did not directly worship celestial phenomena, but regarded these phenomena as established by the gods or taking place in the realm of the gods.
The ancient Babylonians for example certainly took a keen religious interest in astronomy and believed the heavens were under the power of the gods, but they did not regard celestial phenomena as gods or even believe that it was the main home of the gods. They principally thought their gods were manifested by divine images maintained in city temples (Op-???).
Medieval Christianity certainly had a strong tendency, reinforced by Aristotelianism, to regard the observed heavens as part of the literal heaven.
Dante Alighieri (1265--1321) gives the famous retelling of this view in his Divine Comedy. (Yours truly made it through Hell, Purgatory, and Heaven in the translation by Laurence Binyon (1869--1943).)
Caption: "Dante and His Poem, fresco (1465), on the wall of the church of Santa Maria del Fiore in Florence (Florence's cathedral)."
Dante Alighieri (1265--1321) and the Divine Comedy.
Linked source: Wikipedia image http://en.wikipedia.org/wiki/File:Michelino_DanteAndHisPoem.jpg.
Permission: Public domain at least in USA.
Early people were particularly conscious of SIGNS from the gods. The behavior of birds and the entrails of sacrificial animals (i.e., haruspicy) were particularly popular regions to look for such signs at least in the Mediterranean and Middle Eastern worlds.
But celestial signs have always had particularly resonance and their is a tradition that they were aimed primarily at royalty and rulers.
With horoscopic astrology, astro-divination became democratized: the stars determined everyone's character and partially at least influenced their activities. Because most celestial events are regular, but come in a multitude of combinations, astrology could develop a vast realm of possibilities for imaginative astrologers. The exact influences are easy to identify---Venus in your astrological sign isn't hard to read---but giving the influences their exact weight is where the art of the astrologer was needed.
Astrology tended to become understood as a science based on regular cause and effect and less as direct messages from the gods. But direct messages could still occur. Irregular events like comets were considered particularly ominous.
Comet Ikeya-Seki, 1966 (credit: Roger Lynds/NOAO/AURA/NSF)
---Calpurnia, Act 2, Scene 2, Julius Caesar, William Shakespeare (1564--1616)
Astrology is still with us: it's only a click away to your horoscope. There have always been DISSENTERS, of course:
---Cassius, Act 1, Scene 2, Julius Caesar William Shakespeare (1564--1616).
Think of Oedipus and The Mayor of Casterbridge.
Horizon phenomena were often of key interest: rising and settings of the Sun, the Moon, and the fixed stars.
Among many other things, heliacal risings of fixed stars were often noted since they marked times of the year.
The fixed stars rise earlier everyday as the Sun moves east on the celestial sphere.
So if they are rising in the daytime and therefore invisible, they will eventually start rising with the Sun or a bit before---this is their reappearance after an absence from the observable sky.
People who get up with the dawn, notice these thing.
I seem to have gotten my easts and wests confused in this figure.
Hesiod (circa late 8th century BCE) knew this well.
Oh when thistle bursts and cicada,
hid in his tree, shrill and timeless,
sings his song---timeless,
then summer swoons and goat is fat
and wine is good, and maids are riggish,
but burnt are streams and men---burnt dry
by Sirius teaming with the Sun---but I
in the Dog Days love a rocky shade
and Biblos from the vine.
---Hesiod (circa late 8th century BCE), free translation by author of these lectures based on We-77.
But they embodied their astronomical knowledge in monuments.
They made observations using natural horizons and then memorialized them with artificial horizons.
It's 3. Remember the Earth is a point compared to the
celestial sphere.
So anything on the celestial equator will be on a plane
that is perpendicular to the celestial axis (which is also just the Earth's axis)
and that includes the point Earth.
Thus the object will be due east if it is crossing the eastern
horizon any place on Earth.
A physical map of the British Isles. Stonehenge is in southwest England on the Salisbury Plain.
Stonehenge from a distance. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
Stonehenge at closer range. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
Stonehenge as it remains. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
The Heelstone of Stonehenge. Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
The structure to the left could be a portable---which just goes to show how advanced the Stonehengers were.
This is a very crude, schematic map of Stonehenge. I drew it all myself. But you see the Heelstone off to the northeast along ancient avenue. At the Summer Solstice the Sun rises over the Heelstone as seen from the Altar Stone. This is the farthest northward point that the Sun reaches before heading south again.
Caption: "The Sun rising over Stonehenge on the morning of the Summer Solstice (21st June 2005)."
Credit: User:Solipsist (AKA Andrew Dunn).
Linked source: Wikipedia image http://en.wikipedia.org/wiki/File:Summer_Solstice_Sunrise_over_Stonehenge_2005.jpg.
Permission: Licensed under the Creative Commons Attribution ShareAlike 2.5.
There are many other astro alignments at Stonehenge that can be found when viewing the horizon from the Altar Stone.
More extravagant claims of astronomical function are certainly false: e.g., that Stonehenge was an analog computer used to calculate eclipses (Av-71).
Stonehenge is only the most famous monument of alignment astronomy.
There are many others from prehistoric or marginally historic societies all over the world.
For example, the Egyptian pyramids.
The Pyramids of Giza built circa 2500 BCE.
They make you wonder about people who build absurd structures in the middle of the desert. (A remark that had more pith when I taught this course in Las Vegas.)
The faces of the Pyramids are aligned with the cardinal directions: north, south, east, west.
There may be other astro-alignments built into the pyramids (No-9).
Credit: Digital Image Project, Mary Ann Sullivan, Bluffton College.
Note that structures exhibiting alignment astronomy were probably in most cases, including Stonehenge, had multiple uses and significances. Their astronomical use/significance was probably only one among many uses/significances. Stonehenge, for example, was obviously a cult center with religious meanings that probably only included astronomical ones among others. In fact, people probably attended religious and social ceremonies at Stonehenge for trade and holidays too.
The Egyptian pyramids, on the other hand, were primarily tombs for the rules of ancient Egypt.
Why did early societies do astronomy?
As mentioned in the Introduction, there may well have been a few individuals with some purely astronomical interest, but probably that was not the main interest of early societies.
The main interests were certainly religious and, to some degree, calendrical.
Hunters and gatherers and early agriculturalists probably didn't need more than the day-night sequence, the lunar phases, and season sequence for calendars.
But more elaborated societies have terms of office and contracts with termination dates. They would have needed more elaborate calendars depending more detailed astronomical observation.
Still highly detailed astronomy was probably mainly for religious, ritual, and astrological purposes.
In the early literate phase circa 3000--2000 BCE, the region was called Sumer and the people Sumerians.
To later Mesopotamians, the time of Sumerians was a classical age---s Greco-Roman antiquity is to us.
After Babylon became the principle city of the region circa 1800 BCE and the culture and science of the region tends to be called Babylonian thereafter until its principal characteristics faded from history circa 100 CE.
Caption: "Babylon, Iraq (Mar. 21, 2005) - U.S. Army Soldiers assigned to the 155th Brigade Combat Team (BCT), are given a tour of the historical city of Babylon, Iraq as a gesture of goodwill by the Iraqi people in Babil, Iraq. These periodic tours of the ancient ruins are given to service members to learn more about Iraq's history and help boost morale. U.S. Military Reserve and Active Duty personnel are forward deployed to central Iraq in support of Operation Iraqi Freedom (OIF). This is a digital composite of thirteen images to produce a 180-degree panoramic view of Babylon, Iraq. U.S. Navy photo by Chief Photographer's Mate Edward G. Martens (released)."
There has been some reconstruction.
The people in the image are US soldiers---like the armies of Cyrus and Alexander.
How many miles to Babylon?
Three-score and ten.
Can I get there by candle-light?
Yes, there and back again.
If your heels are nimble and light,
You will get there by candle-light.
Linked source: Wikipedia image http://en.wikipedia.org/wiki/File:The_historical_city_of_Babylon.jpg.
Permission: Public domain at least in USA.
The Sumerians and Babylonians developed novel mathematical and astronomical techniques.
The Babylonian astronomers, in fact, developed as sophisticated mathematical, predictive astronomy far in advance of the simple alignment astronomy of earlier civilizations.
What and why of predictive astronomy?
How do we know about Babylonian astronomy?
They Wrote on Clay (1938, Edward Chiera, 1885--1933).
Caption: "List of gods in order of seniority: Enlil, Ninlil, Enki, Nergal, Hendursanga, Inanna-Zabalam, Ninebgal, Inanna, Utu, Nanna. Sumerian language cuneiform script clay tablet, Sumer, 2400-2200 BC, 1 tablet, 4,7x4,4x1,7 cm, single column, 5+5 lines."
Credit: Sumerian scribe.
Linked source: Wikipedia image http://en.wikipedia.org/wiki/File:Sumerian_MS2272_2400BC.jpg.
Permission: Public domain at least in USA.
The Sumerians and Babylonians used a sexagesimal number system or base-60 system for mathematics and astronomy.
They used the sexagesimal system consistently only for these purposes (Ne-17). They used other systems including the ubiquitous 10-based system in other contexts usually. The 10-based system is common: everyone counts on their fingers. A 20-based system may means you are down to your toes.
Mind you, they didn't have the compact notation we have and they didn't understand the concept of using symbols to represent unknowns.
The predictive astronomy of the Babylonian astronomers had simple beginnings in using cycles.
Early evidence of this is the Venus Tablet of Ammisaduqa from circa 1600 BCE.
Ammisaduqa (c. 1582--1562 BCE, short chronology) was a king of the First Dynasty of Babylon which was the dynasty of Hammurabi (c. 1728---1686 BCE, short chronology).
The original Venus tablet (from which many copies were made) dates from circa 1600 BCE.
It shows that the Babylonians as early as that could rely on cycles to make relatively accurate predictions.
Most Solar System motions repeat if you wait long enough. Venus' motions relative to the fixed stars and the Sun repeat approximately about every 8 years (No-29). The Venus tablet exhibits this knowledge.
Credit: ancient astronomers and copyists; modern credit: Langdon et al. (1928) (believed to be public domain).
You can build up cycles for the other planets and for eclipses. For example, all eclipse phenomena repeat approximately about every 18 years: this is called the Saros cycle by moderns.
Thus a primitive predictive astronomy can be built up from cycles. The Babylonian astronomers did this first.
But they advanced.
In the period 400 BCE -- 100 CE, Babylonian astronomy culminated.
Ephemeris is a singular which is hard to remember.
Ephemerides is the plural ephemeris which is also hard to remember.
But we have no evidence that the astrophysics was of any interest to them: i.e., attempting to understand the cosmos in terms of physical laws and a 3-dimensional structure.
They may well have been satisfied with a DOME MODEL of the the cosmos in which the celestial objects were manifestations of the gods.
But, in fact, we don't know that much.
Our understanding of their mathematical astronomy just comes from calculational and ephemeris tablets.
There is no physical explanation or any explanation actually. All we know is that the tablets were written in priest-like surroundings.
Before going on we should mention that Babylonian exact sciences had only two GOLDEN AGES: (1) circa 1800--1600 BCE in pure math (Ne-30); (2) circa 400 BCE -- 100 CE in mathematical astronomy.
There were long stretches of time in a literate culture that spanned from 3000 BCE to 200 CE in which not much development happened.
The pattern of GOLDEN AGES: and stagnation seems to be typical of science in traditional societies.
The ancient Greeks had a GOLDEN AGES, and so did Medieval Islamic society.
So did traditional Chinese society and Indian society---probably a few, but yours truly is not so well informed on these societies.
Part of the explanation is that science is a marginal activity in traditional societies. Only a few individuals practice it and societal support tangible and intangible is chancy.
A few atypical individuals---well let's call them geniuses---may feedback on each other over a few generations to create significant progress. But the chain is broken by chance and stagnation seems to result.
Fortunately, the achievements are usually preserved and can be built on later.
Science in modern society since circa 1600 is radically different. It is relentlessly progressive and strongly supported by society. This change in the development of science is called in historical research the Scientific Revolution. The Scientific Revolution or at least its inner core is located in thee 16th century and 17th century.
Ancient Greece circa 550 BCE. Click on image for magnification and credit.
The earliest natural philosophers---the Pre-Socratic philosophers---were from Ionia (western Turkey): e.g., Thales (c. 624--c. 546 BCE), Anaximander, Anaximenes, and Pythagoras (c. 570--c. 495 BCE) all in the 6th century BCE.
Thales, Anaximander, and Anaximenes all tried to create theories of the cosmos that were based on ELEMENTARY PRINCIPLES without invoking anthropomorphic gods.
Thales---the first natural philosopher by most reckoning---thought the basic substance was water. Anaximenes thought it was air. Anaximander thought it was the Boundless.
Pythagoras is famous for founding a sect that believed that the world is based on mathematics. This could have led to mathematical physics, but in fact led to number mysticism.
A great advance was made by Parmenides of Elea (early 5th century BCE) (in southern Italy).
He is the first person to propose that the Earth was a SPHERE---although maybe Pythagoras beat him to it.
Parmenides also thought that the cosmos was spherically symmetric and centered on the Earth.
His reasoning insofar as we know it seems to have been philosophical: the spherical shape would allow perfect balance and this sustained the cosmos (Furley, 1987, p. 54--56).
But he may have had more empirical reasons for proposing a round Earth. In any case, Aristotle (384--322 BCE) later summarized the empirical evidence for the round Earth:
Recall in astro-jargon, altitude is height above the horizon.
Answer 1 is right.
The ancient Greek theatre (circa 300 BCE) in Segesta, Sicily.
This is not so far from Parmenides's home town, but he'd have had to cross water to get there.
The ancient Greeks liked to have view in their theatres.
I sat under that tree to the lower left and had a snack in 2006jun.
Credit: Digital Imaging Project of Mary Ann Sullivan, Bluffton College; download site Digital Imaging Project's Greek Theater, Segesta, Sicily site. The download site gives more information.
Assuming the round Earth model and that the Sun is very distant from the Earth, it is possible using measurments of shadow lengths at different latitutes and a bit of geometry to find the radius and circumference of the Earth. This was done by Eratosthenes (c. 276--c. 195 BCE) found that Earth's radius was of order 7000 km---but he didn't know it in kilometers, of course. The actual modern mean value for the Earth (which isn't perfectly spherical) is 6371.0 km. Old Eratosthenes measurement wasn't so bad.
The cosmological models Pre-Socratic philosophers were largely based on reasoning from simple, crude observations, without much that can be calledl detailed observations or experiment. The models can be described as rational myths.
But they were very interesting in themselves and in being the origin of cosmology.
The cosmology of the atomists Leucippus (first half of 5th century BCE) and Democritus (c. 460--c. 370 BCE) seems most impressive.
Caption: "Democritus meditating on the seat of the soul by Léon-Alexandre Delhomme, 1868."
Democritus (c. 460--c. 370 BCE) was the foremost exponent of atomism among the ancient Greeks.
Credit: User:Jean-Louis Lascoux.
Linked source: Wikipedia image http://en.wikipedia.org/wiki/File:Democrite.JPG.
Permission: Use under GNU Free Documentation License.
They invented atoms and Democritus anyway posited many worlds forming of atoms out of an infinite, eternal universe full of atoms.
Democritus thought of these worlds as vortices surrounded by membranes. These worlds existed for finite times.
Our own vortex membrane is the celestial sphere thought of as a real surface.
It swirls around us carrying the fixed stars.
The vortex idea is not so hard to appreciate when you think about how the sky is carried around every day by celestial sphere
GEMINI NORTH is an 8-meter telescope on Mauna Kea, Hawaii.
Mauna Kea is at 4,145 m (13,600 ft) and is one of the world's best observing sites---located fortunately in one of the world's best tourist sites---still the air is thin up on the mountain.
Here we see a swirl of stars in a long exposure photograph.
The star trails seem to be about 30 degrees (1/12 of 360 degrees), and so the exposure was about 2 hours (1/12 of a day).
The center of the star paths seems to be below the level-ground horizon, and so I think we are probably looking south and the stars are swirling about the SCP.
There is METEOR trail just about perpendicular to the star trails.
The red-yellow streaks are the tail lights of cars driving up the mountain during the exposure. In long exposure photograph, the tail lights were at every point along there path at the ``instant'' of exposure.
Looking at this image it is possible to why some of the ancient Greek philosophers imagined the cosmos as a giant VORTEX (Fu-140).
Credit: Gemini Observatory /NOAO /AURA/NSF.
But Democritus was old-fashioned in one sense: he thought of the Earth as being a flat residue at the bottom of the membrane.
He may have thought that the universe was anisotropic and that there was a universal down direction in which things fell at least inside of the membranes.
Democritus's cosmology bears a passing resemblance to the modern theory eternal inflation---which makes one wonder if humans are somehow constrained to imagine only certain possibilities.
What about planet theory? Where were the Pre-Socratic philosophers?
The astronomers of those times had a major problem---that, of course, had been around since forever.
The distance problem.
In the 5th century BCE, the first planetary model of the Solar System that we know of appeared.
This the model of Pythagorean Philolaus (c. 470--c. 384 BCE)
It was partially inspired by philosophical notions.
Actually, Philolaus may not have thought of the celestial sphere as a fixed surface.
He also thought that the Earth was flat. It revolved around the Central Fire (fiery body) always turning it's bottom toward the Central Fire.
This meant that the Earth rotated and this accounted for most of the motion of the celestial sphere.
The Counter-Earth was posited to keep the universe in balance, but oddly it isn't on the same orbital path.
Philolaus's model is actually only very approximately qualitatively accurate and there is no reason to think anyone every tried to make it quantitatively accurate.
But it is remarkable that, however odd it seems, the first planetary model of history has a rotating Earth and is NOT geocentric.
It's not heliocentric either---it's Central Fire-ocentric.
The model of Philolaus was remembered, but not influential.
From about 4th century BCE, most astronomers in Greco-Roman antiquity, the Islamic Golden Age (c. 9th--13th centuries) and Medieval Europe thought in terms of a finite universe enclosed by the celestial sphere thought of as a real surface with a round Earth at the center.
They were following Aristotle in this regard.
The ancient Greek astronomers did try to qualitatively and quantitatively understand the geocentric, finite cosmos.
Below is a simplified version for illustration of model of Eudoxus of Cnidus 410 or 408--355 or 347 BCE) for explaining the motion of the Sun around the Earth.
The fixed stars are on an outer sphere---the celestial sphere conceived of as a real thing---and this sphere carries around the Sun sphere.
The celestial sphere rotates once per day.
The Sun sphere rotates once per year.
The two motions are superimposed and this accounts for the appearances.
Eudoxus's model was the first model to quantitatively explain the more difficult celestial motions in terms of 3-dimensional geometric structures. It dit qualitatively give retrograde motions for the planets.
Much more elaborate models were needed for the planets---in particular, to explain their retrograde motions quantitatively.
But not in the Parthenon.
The Parthenon from the west. The Parthenon is on the Acropolis of Athens. Click on image for credit.
Aristotle's cosmology was a development from Eudoxos's model. He used spheres all concentric around the Earth to account for all the celestial motions. Beyond the outermost sphere was nothing---not even empty space---just nothing.
A cartoon of the Aristotelian cosmos.
Aristotle (and other Greeks) argued that the Earth had to be at rest since otherwise we would be spun off or blown off by terrific winds. In any case, we would feel the motion.
Relative to unaccelerated frames, Newtonian laws of physics apply directly: e.g., in a smoothly moving train or plane. There are no strange ``forces'' unless you accelerate: speed up, slow down, or turn.
Aristotle also postulated a radical distinction between Earth and Heaven. The Heavens were a realm of eternal cyclic motions of perfect bodies. Gods (or in later monotheistic versions angels) propelled the spheres.
The Earth, on the other hand, was imperfect and changing.
Galileo Galilei (1564--1642) and other Copernicans of the 17th centuries would try to find stellar parallax But the stars are really remote by Solar System length scales and stellar parallax is minute even for the closest stars. Stellar parallax was not finally discovered until 1838 (No-419).
In later Antiquity, in Medieval Islamic and European cultures, and in the Renaissance, Aristotle for many---but not all---became the highest or even the SUPREME AUTHORITY in philosophy including natural philosophy.
Aristotle seemed to offer to the educated person a complete philosophy---except in the religious dimension. And, of course, there is a reason for this---he was a broad and deep thinker.
In particular, Aristotelian physics and Aristotelian cosmology became a philosophical dogma.
In fact his, cosmology is not quantitatively correct---it's not even qualitatively correct if you look at it closely. You can't produce accurate ephemerides from his model. I don't know that anyone ever tried to.
Strict Aristotelians---those pesky varmits---rationalized that Aristotle had got it right as far as human understanding could reach.
But a mathematical tradition in astronomy did develop.
The most important of the mathematical Greek astronomers, we now discuss.
As a mathematician, he was the greatest expert on ellipses until circa 1500 give or take a couple of centuries.
But he also invented the idea of deferent and epicycle planetary orbits which turned out to be a big detour from the truth---since the planetary orbits are physically ellipses to first approximation.
We discuss deferent and epicycle planetary orbits below.
How could Apollonius have got it wrong?
The data and theoretically understanding at the time and until circa 1600 weren't advanced enough to show that elliptical orbits were conceptually better.
In fact, with enough epicycles on top of epicycles, the deferent and epicycle approach will fit data to high accuracy.
The deferent and epicycle approach is still for fits for some kinds orbital motion: i.e., orbits around galactic centers (Shu-265--267). It can be used for mathematical decomposition of complex orbits.
A key factor is that the speed of planets on elliptical orbits is not constant.
Until the time of Galileo Galilei (1564--1642) and Johannes Kepler (1571--1630) dealing with non-constant speeds directly was considered too difficult either conceptually or observationally.
He, building on a long tradition of mathematical astronomy both in the Babylonian and Greek worlds, developed full deferent and epicycle models for whole the Solar System.
With these models he could quantitatively predict the celestial motions of the planets and, in particular, explain their retrograde motions.
Although not a strict Aristotelian, Ptolemy basically followed Aristotle's physical ideas and remained a strict geocentrist.
Ptolemy did admit non-geocentric models were geometrically possible, but he said they were physically absurd.
A simple deferent and epicycle model is shown below. A model like this could be constructed for all the planet, Sun, and Moon.
The epicycle is a small orbital path carried around at a constant speed on the main orbital path, the deferent.
An astro-body then orbits on the epicycle.
Non-circular and non-constant-speed motion is obtained by the compounding of the motions on the deferent and epicycle.
retrograde motion was explained by the epicycle motion superimposed on the deferent motion. The two compounded motions could add up to a westward of the planet on the sky.
But there is no way to know the overall structure. The model for each object could be put at any distance and in any order from Earth.
Ptolemy did actually give an order and inferred distances, but his arguments were not conclusive for other people---of course, since his models were wrong, his arguments couldn't be conclusive.
Below is a cartoon of Ptolemy's full model for the planetary system.
Ptolemy actually needed more tricks to fit the data.
He needed to have the Earth off-center making the orbits eccentric.
So his models weren't exactly geocentric.
More scandalously he invented the equant.
This was philosophical/physical dogma that conformed to the perfection of circles and allowed one to avoid head-on confrontations with non-constant speeds.
Complicated motions were constructed by compounding uniform circular motions on Aristotle's celestial spheres or by the deferent and epicycle models.
Ptolemy agreed in principle, with the uniform circular motion principle, but violated this dogma by making deferent angular uniform speeds around an equant which was displaced from the center of the deferent on the opposite side from the Earth's position.
This is the crime of Ptolemy.
Quite rightly, posterity would chide Ptolemy for inventing the equant---which we could call a fudge factor or ad hoc hypothesis---he violated his own physical principles.
They arn't UNIQUE.
By varying the size of the deferent and epicycles and adding epicycles on epicycles, varying the orbital speeds, and fooling around with equant, you can create endless models that give the same predictions to within about the same accuracy as those of Ptolemy
Ptolemy's models are in fact mathematical decompositions---non-unique ones.
For 13 centuries after Ptolemy, astronomers in the Indian, Persian, Islamic, and European cultures would try to improve on Ptolemy's models and get rid of the dratted equant.
They found variations that were as accurate, but not really more accurate and they couldn't tell which was right.
Yes. Aristarchus of Samos (c. 310--c. 230 BCE) 3 centuries before Ptolemy.
We only know he proposed it from a few comments in surviving ancient writings.
But those comments don't tell us Aristarchus reasons for invoking heliocentrism.
It's reasonable to guess, they are the same reasons that led Copernicus to heliocentrism.
We'll discuss those reasons below in the section Nicolaus Copernicus (1473--1543) and Heliocentrism.
Aristarchus is a precursor of a discovery--- a person who discovers something, but fails to make the world appreciate it's value---a prophet without honor in his time.
The mathematical astronomers of the Medieval Persian, Indian, Islamic and European societies continued to fiddle around with geocentric deferent and epicycle models.
They didn't really improve them.
On the other hand, they did improve MATHEMATICAL TECHNIQUES.
The trigonometric functions were developed in Indian-Islamic worlds as were Arabic numerals which came replace the clumsy notations of the past: e.g., Cuneiform, Greek, and Roman numerals.
With Arabic numerals the base-10 system began to dominate.
A base-12 system might have been handier, but since our hands have 10 fingers . . .
Decimal fraction were also developed perhaps independently in several places. An important treatise on them was written by by Jamshid Al-Kashi (c. 1380--1429) who worked at Samarkand Observatory of the Samarqand ruler Ulugh Beg (1393/4---1449) (No-200. Simon Stevin (1548/9--1620) later greatly enhanced the use of decimal fraction in the European context.
Omar Khayyam was a considerable mathematician and astronomer. He is famous for is work on cubic equations and his attempted calendrical reform---and as a poet.
But actually all poetry attributed to Omar Khayyam him was collected and added to in later centuries. His contemporaries did not note him as a great poet. See, e.g., Petri Liukkonen 2006, Omar Khayyam = Umar-i-Khayyam (1048-1131) It's not clear if he wrote any of it or was a poet at all, except in legend. His poems may be all pseudepigrapha.
Caption: "At the Tomb of Omar Khayyam" (Omar Khayyam (1048--1123)).
Credit: Jay Hambridge (1867--1924), From Constantinople to the Home of Omar Khayyam, pre-1911.
Linked source: Wikipedia image http://en.wikipedia.org/wiki/File:At_the_Tomb_of_Omar_Khayyam_-_by_Jay_Hambidge.jpg.
Permission: Public domain at least in USA.
Chaucer can only be considered an amateur adept in astronomy, but he did write a treatise on the astrolabe which is a interesting combination of analog computer and observational tool.
But he certainly was a poet.
He often worked astronomical allegories into his poems which often go right past the modern reader including modern astronomers. For example, the day of Chauntecleer's unfortunate episode with the fox is 1392 May 3, Friday as internal evidence shows (No-233, HH-400): Chaucer was using Friar Nicholas of Lynn's (c. 1330--after 1411) astronomical tables:
---The Canterbury Tales: The Nun's Priest's Tale (HH-400).
As it happens, the Sun was passing through the Pleiades asterism (M45) (an actual physical cluster of stars) in Taurus on that day. In Medieval Europe, the Pleiades were often called the Seven Chickens: Chauntecleer and his wives are, among other things, allegorical to Sun and Pleiades (No-233).
Caption: "Image of Geoffrey Chaucer (c. 1343--1400) as a pilgrim from Ellesmere Manuscript in the Huntington Library in San Marino, California. The manuscript is an early publishing of The Canterbury Tales."
Credit: Medieval artist, User:Bkwillwm.
Linked source: Wikipedia image http://en.wikipedia.org/wiki/File:Chaucer_ellesmere.jpg.
Permission: Public domain at least in USA.
``What is truth?'' as Copernicus may have asked.
He studied in Italy for most of the decade 1496--1506.
In Padua where he was at the University of Padua, Copernicus would have known---one assumes---the church of Sant'Antonio built circa 1290: Galileo would know it---one assumes---when he was a professor in Padua in 1592--1610.
The church of Sant'Antonio (facade) in Padua, Italy.
Copernicus was student
in Padua (Padova in Italian)
studying astronomy, astrology, and medicine in 1501--1503.
One should note that in those days astrology was considered a
necessary qualification for medicine: a doctor had to be able
predict the effect of the stars on health.
Galileo was a professor of
mathematics and astronomy at the
University of Padua from 1592--1610.
Credit: Digital Imaging Project of Mary Ann Sullivan, Bluffton College; download site Digital Imaging Project's Padua, Italy site. The download site gives more information.
Answer 2 is right, although the other answer is arguable too since
arches have an aesthetic appeal.
Note the answer is also why planets and stars are ROUND. Their self-gravity overcomes pulls them into a round shape. Only compression resistance of their materials sustains them against collapse.
Heliocentrism is the theory that the Sun at the center of the Solar System or, for Copernicus and most of his early followers, the center of the cosmos.
Copernicus published his detailed theory in his book On the Revolutions of the Heavenly Spheres in 1543: the actual Latin title is De Revolutionibus Orbium Coelestium.
ONE DIAGRAM shows you why Copernicus turned to heliocentrism.
Recall the astronomical unit is the mean Sun-Earth distance.
One assumes exactly heliocentric circular orbits as a first approximation.
One finds the orbital angular speeds.
Then one can calculate the angle between any planet and the Earth as measured from the Sun for any specified time from some known initial angle.
At that time, one measures the angle between planet and Sun from the Earth and uses the law of sines to find the Sun-planet distance in units of the astronomical unit.
----Copernicus, On the Revolutions of the Heavenly Spheres (1543)
Now the absolute distances were not known at all accurately since the astronomical unit was not known in terms of the Earth's size.
Only in the 17th century would the astronomical unit begin to be estimated accurately (No-351). Copernicus used the ancient Greek value for the astronomical unit which was about 23 times too small (No-294).
But Copernicus had found the ``chief thing,'' not by new observations, but just by having the right theory.
Of course, heliocentrism could have turned out to be wrong.
But the modern way of judging theories which cannot be tested yet by observation, is by how many important results can be deduced from them and how fruitful they are in leading to new developments.
In fact, even if a theory turns out to be wrong, it is still a great theory if it is fruitful in furthering development.
If even it had been wrong, heliocentrism wa a great theory because one can deduce from it important results that can be tested by observation that were in principle possible if not practicable yet in Copernicus's time.
Copernicus's heliocentrism---or, as one can call it in the century or so after Copernicus, Copernicanism---was recognized by as great theory by those astronomers who we see retrospectively as most modern and progressive: e.g., Galileo Galilei (1564--1642) and Johannes Kepler (1571--1630).
Copernicus's total theory of the Solar System is in many ways old fashioned.
In order to make a predictive model, he had to use epicycles and other ancient devices. He still used the celestial spheres of Aristotle. In fact, except for the transposition of the Earth and Sun, his models are much like Ptolemy's in mathematical construction. He was not a complete radical in mathematical astronomy.
Modern scientists see the equant and the principle of uniform circular motion as dead isssues. Which is true, but it's presentism to forget that they were important issues to astronomers from Apollonius of Perga (c. 262--c. 190) to Johannes Kepler (1571--1630)
His model totally upset physics as it was then understood: i.e., Aristotelian physics which we won't bother to detail here---but a key point is that the Earth had to be at rest or else we would feel its motion and everything would need obvious forces to keep moving with the the Earth.
Copernicus made the Earth a planet.
Somehow it had to carry its own frame of rest with it.
If Earth was a planet, the other planets therefore could be like the Earth.
Also since stellar parallax was not observed, the star sphere had to be extremely remote. The universe had to be big by comparison to what people had thought.
Aristotelian cosmology with its unchanging Heavens and resting Earth was totally wrong if Copernicus was right.
There were some early reactions to Copernicanism up to circa 1600. (In Europe, of course. No else in the world would hear or think much of it for a couple of centuries.)
Thus, Copernicanism was potentially a heresy on both sides of the religious divide. Note Copernicus's life spanned the Reformation and the beginning of the wars of religion in Europe.
Copernicus was quite aware of this potential heresy problem---he was a Catholic Church lawyer after all.
He tried to defend his orthodoxy of his theory by dedicating his book to Pope Paul III (1468--1549, pope 1534--1549) and addressing himself only to astronomers, not to theologians or the general public.
In fact, one of the reasons for delaying publication of his theory until he was near end of his life may have been to ensure he wouldn't be around to face awkward questions.
On both Catholic and Protestant sides there was some negative feeling, but a heresy in which no one believes doesn't excite a lot of official notice.
Not an absolutely new idea, but a new idea in the context of the Copernican system.
This should be 16th century Copernicans.
His equipment was not at all novel---in essentials it had all existed for millennia. What was novel was his commitment to reducing mechanical errors. Tycho perceived that one of the problems of astronomy was that new observations were as poor as the old ones.
To RENOVATE ASTRONOMY you needed better observations, not just new ones.
The utility of Tycho's data comes with its use in the models of Kepler which we'll come to below.
SN 1987A in the Large Magellanic Cloud.
Modern Supernova SN 1987A is the bright, pointy star near the center. It exploded in 1987 (hence its name). SN 1987A is in a dwarf galaxy, the Large Magellanic Cloud (LMC), that is a satellite of the Milky Way. Many of the stars in this picture are foreground stars in the Milky Way The pink region is the 30 Doradus, a bright emission region gas in the LMC. It's a star formation region. Incidentally this most famous of all modern supernovae was discovered by Ian Shelton, the brother of my UNLV colleague David Shelton.
Credit: Marcelo Bass, CTIO/NOAO/AURA/NSF .
Tycho did not know that the new star was a supernova.
But Tycho did prove that the new star was beyond the Moon. Thus he proved there was change in the Heavens that Aristotle was wrong.
In 1577, Tycho proved that the great comet of that year was also beyond the Moon. Aristotle had argued that comets were sublunary, and so didn't violate the immutability of the heavens.
Tycho also showed that the comet's orbit took it through the celestial spheres---those crystalline spheres that carry the planets. He concluded the crystalline spheres did not exist.
Tycho's disproofs of Aristotelian cosmology were only verifiable by a few other astronomers, and so most of the scholarly world could and did ignore them.
That Tycho's disproofs were not widely accepted is reasonable. There are many claims in science and other fields that are made and never verified. Often you have to wait until the issue matures.
Aristotelian cosmology, however, was beginning to shake on its foundations.
Tycho's other great achievement was the Tychonic system. (He was anticipated by others partially at least.) The Tychonic system is the Copernican system turned on its head.
All the astro bodies, except Earth and Moon orbit the Sun and the Sun and Moon orbit the Earth.
Geometrically, the Tychonic system is valid. If you take the Earth, as your reference point, the Tychonic system follows.
But in modern physics, the Tychonic system is not dynamically relevant. It is the mass and gravity of the Sun which dominates the motion and the Sun sets the approximately UNACCELERATED reference system of the Solar System. So the Sun is the center of the Solar System in the modern view.
Tycho and his contemporaries did not have modern physics, of course: that would come with Newton's (1643--1727) Principia in 1687.
But Galileo and Kepler believed that the true physics would be one in which the Sun was the physical center of Solar System motion. This belief was based on their weighing of the evidence available---and, of course, they were correct---as we know now.
Many of Tycho's contemporaries felt the Tychonic system was the happy mean. It retain some of the Copernicus's system. It had no equant (at least if one didn't want one), it explained retrograde motion as well as Copernicus's system, and it gave all the relative Sun-planet distances just like Copernicus's system.
It was a new system that was not too radical.
The Imperial Mathematician was traditionally the court astrologer, but Kepler was given freedom to pursue novel research.
Luckily, Kepler got hold Tycho's data: Tycho's astronomically worthless heirs would have sat on them dog-in-manger style, and thus have rendered much of Tycho's work barren.
Kepler, unlike Tycho, was a convinced Copernican from his college days (Tuebingen 1591).
Using the correct theory and the best data every available he was able to find the true motions of the planets. Remember Copernicus still used epicycles and the like.
Kepler did NOT have the right physics although he tried to find it. But he did have one correct guiding physical principle: the distance from a planet to the Sun is the key variable in determining the shape of the orbits and the motions.
So it is NOT true to say that Kepler's discoveries were mere empirical fits to the data.
Kepler's discoveries did take a lot of calculations.
Kepler's most important discoveries are his 3 laws of planetary motion.
Now Kepler's discoveries did not prove heliocentrism.
Geometrically his models are consistent with both the Tychonic system (in its main idea) and heliocentrism. You just had to make decision which point to take as the origin.
But the Earth obeys the three laws just like a planet if you take it to be a planet.
If you take the Earth to be center of a Tychonic system, then you have a double system with the Sun as secondary center. The physical explanation of the latter arrangement would have to be more elaborate than of the former.
Why should the huge Sun dominate all the planet motions, but then in turn be dominated by the tiny Earth? It didn't seem physically reasonable to Kepler.
Kepler's discoveries with their comparatively elegant interpretation from the heliocentric view and the accuracy of the Rudophine Tables did EVENTUALLY help to convince many people that the heliocentrism was probably the right physical system even though the right physics had not yet been invented.
Note the word EVENTUALLY. Kepler's work in mathematical astronomy was inaccessible to many---particularly those steeped in Aristotelianism. Thus, his impact on the Copernican debate in his lifetime was limited.
Galileo's telescopic discoveries would have a much more dramatic and immediate impact as we will see.
How did Kepler and Galileo interact?
They were contemporaries after all.
But they never met: Kepler never got south of the Alps and Galileo never north of them.
They corresponded on two occasions, but never had a complete meeting of minds.
Galileo never absorbed Kepler's prime work (i.e., Kepler's 3 laws of planetary motion). He may have understood it, but he never used it. Why?
We can only speculate. After 1616 when Copernicanism was a effectively condemned as a heresy by the Catholic Church, it would have been impolitic for Galileo to have openly cited Kepler, who was an open Copernican and a Protestant. But even before 1616 and in private Galileo made no use of Kepler. It's possible he distrusted Kepler's approach to science. Galileo was utterly unmystical: a true heir of Aristotle, the experimentalist (but not of dogmantic Aristotelians) and Archimedes (287?--212? BCE) (the greatest Greek physicist). For example, Galileo had no belief in astrology though he was required to teach it since, then as now, medical students needed astrology in order to diagnose and prescribe.
Kepler, on the other hand, was a sort of mathematician mystic: an heir of Pythagoras (c. 570--c. 495 BCE) Plato (428/427--348/347 BCE). He started out with a deep faith in astrology though he understood that contemporary practice was utterly corrupt. In later life, after failing to make any progress in developing a scientific astrology, he seems to have become a bit cynical about it and perhaps regarded it primarily as a funding source.
We can see that Kepler and Galileo were both working toward modern science, but from somewhat different directions. But that may not have been apparent to Galileo who may have thought Kepler a fantasist.
And Kepler, though he highly valued Galileo's astronomical discoveries, never understood Galileo's achievements in physics probably mainly because Galileo didn't get around to publishing most of them until after Kepler's death.
Kepler---who was a German---died in 1630 in the midst of the Thirty Years' War.
---from a letter of Kepler's from his last years.
Just an interesting historical tidbit.
---Claudius, Act 2, Scene 2,
Frederick Rosenkrantz and Knud Henriksen Gyldenstierne were cousins of Tycho Brahe and part of the Danish embassy to England in 1592 where William Shakespeare may have noticed them. He possibly cast them in bit parts in Hamlet.
Rosenkrantz would later meet Kepler. The link between Kepler and Shakespeare is established---I knew there had to be one. They may never heard of each other---although Kepler's fame as an astrologer may have penetrated to England---but maybe there was only 1 degree of separation (see Wikipedia: Six degrees of Separation).
He is often cited as the single most important or at least most representative figure in the transition from traditional science to modern science---which we call the Scientific Revolution.
Galileo is also known for a number of scientific quarrels. He won most of those---but in some cases only posthumously.
Galileo's famous demonstration of dropping the balls from the Leaning Leaning Tower of Pisa.
Answer 1 is right.
Galileo held that they should reach the ground at the same time in the ABSENCE of air drag. You may never be able to reach the actual ideal case of no air drag experimentally, but you can approach it, and so envision it.
This process of approach to and envisioning of IDEAL CASES was one of Galileo's scientific principles---one that has passed on into modern scientific work.
At the beginning of analysis, don't start worrying about all the complications. Solve the ideal problem first and then add secondary effects to be solved as perturbations.
The Leaning Tower of Pisa from which Galileo did his famous ball dropping demonstration. Click on the image for credit.
Galileo did not invent the telescope. It was invented in about 1608 in the Netherlands by eye-glass makers (see Wikipedia: Telescope Invention).
Eyeglasses had been invented sometime in the period 1280--1300 in Europe (see Wikipedia: Invention of eyeglassses) and eyeglass makers were common by the 17th century.
Given that crude telescopes can be made just by fooling around with a couple of lens or a lens and spherical mirror, it seems that the telescope was discovered rather late in the day.
Galileo when he heard of the telescope put his experimental skills to work and quickly made the best in the world then available.
His telescopes were still very crude instruments with much poorer optical quality than even a cheap modern telescope. For example, they didn't focus all colors in the same place: this is called chromatic abberation.
Certainly, he reported them first: most of them in his popular bestseller Sidereus Nuncius (in English The Star Messenger), and so overnight Galileo became the most famous natural philosopher in Europe. The main discoveries and their major implications can be summarized:
The naked-eye stars (of which there are only a few thousand in fact) were only a small fraction of all the stars. The bigger the light-gathering power of the telescope the more stars you saw. In other words, there was no obvious limit to how many stars there were.
Also the Milky Way was at least partially resolvable into stars. Previously the Milky Way was just a band of milkiness on the sky as it's name suggests---the milky road.
Also stars were still unresolved. They were still point-like.
Nothing had been proven, of course, but the idea that stars were suns spread throughout a large or infinite space as Thomas Digges's (1546--1595) and Giordano Bruno (1548--1600) had at least partially suggested began to seem plausible.
To the right is Galileo's own Moon map from 1609 December 3. In the bright half is the hindquarters (or ears depending on which tradition you follow) of the Rabbit in the Moon, but I can't identify the big crater. Galileo seems to have exaggerated the size of one several craters in the vicinity.
The Moon was clearly a body not altogether unlike the Earth. It was not a perfect sphere as in Aristotelian cosmology.
And if the Moon was Earth-like, then the Earth was Moon-like. The argument that the Earth could not be a planet because it was unlike the celestial bodies vanished.
The moons orbited Jupiter, not the Earth nor the Sun. The Earth was not the only body that could be a center of motion.
Also the smaller bodies clearly orbited the larger body. The Sun was known to be vastly bigger than Earth. Could a bigger body orbit a smaller body? It began to seem as if it shouldn't. Kepler had thought it shouldn't all along.
Also it was now possible for Earth to be a planet and still have a moons. It had been argued that the Earth couldn't be a planet since planets don't have moons.
The nearly full phase of Venus showed that Venus clearly passed behind the Sun.
In the Ptolemaic model, Venus orbited on an deferent that was closer than the Sun: full phases were not possible. Ptolemy was just wrong about the Venus orbit.
Aristotelian cosmology and the Ptolemaic system were demolished.
But, of course, not everyone saw that at once.
The observations were tricky and not everyone had adequate telescopes. Even when they had seen the new discoveries with their own eyes, some dyed-in-the-wool Aristotelians could not accept them. It isn't very easy to accept that your whole cosmology is evaporated---especially if you are getting on in years.
But the telescopic discoveries were not abstract mathematical discoveries like Kepler's or hard to duplicate like Tycho's new star and comet observations.
But the telescopic discoveries did NOT prove heliocentrism.
Anser 3 is right
Question Could heliocentrism be proven physically in circa 1610?
The physical sense of Galileo and Kepler was that heliocentrism would prove correct was correct as we know now. Personally neither of them had any strong doubts.
Of course, the reasonable person of the time surveying the evidence might have suspended judgment as no doubt many did.
As is well known, the leadership of the Catholic Church at that time didn't suspend judgment.
It must be pointed out that many in hierarchy of the Church were not closed-minded on the issue, but they weren't in charge of orthodoxy.
In 1616, heliocentrism as physically real was condemned by a Church decree as a heresy effectively.
Hypothetical discussion of heliocentrism was allowed though.
Galileo obtained permission from an old friend who happened to have become Pope Urban VIII (1568--1644, pope 1623--1644) to write a book that would treat heliocentrism favorably, but HYPOTHETICALLY as something that could NOT be proven.
Caption: Frontispiece and title page of Dialogue Concerning the Two Chief World Systems (1632)
The people in the frontispiece are not the interlocutors of the Dialogue, but are Aristotle (384--322 BCE), Ptolemy (c. 90--c. 168 CE), and Nicolaus Copernicus (1473--1543)---if I recall correctly.
The condensed text of the book translated into English is here.
Credit: 17th century artist and printers; User:David J. Wilson.
Linked source: Wikipedia image http://en.wikipedia.org/wiki/File:Galileos_Dialogue_Title_Page.png.
Permission: Public domain at least in USA.
Galileo only at the end in deus-ex-machina fashion reverts to the stance that heliocentrism could not be proven and that God could have arranged the cosmos in a way that was profoundly different from what human reason and observation could discover.
Urban when he had become fully informed about the book---already then circulating---took umbrage.
He thought Galileo was taking him for a fool. That very probably was really that (Fantoli 2003). (Certainly, not my own conclusion by the way.)
Galileo may just have thought he had more leeway than he did. Maybe a bit of wishful thinking.
I don't think there is a consensus conclusion on this point, but maybe there is.
Credit: Digital Imaging Project of Mary Ann Sullivan, Bluffton College; download site Digital Imaging Project's Colosseum, Rome site. The download site gives more information.
St. Peter's Square, Vatican City, Rome.
Credit: Digital Imaging Project of Mary Ann Sullivan, Bluffton College; download site Digital Imaging Project's St. Peter's, Vatican City site. The download site gives more information.
He really had no choice: he was a perfectly sincere Catholic and hardly would have relished going to the stake as an enemy of the faith.
And dying a heretic would have sentenced his family, friends, and patron to embarrassment.
After his trial in 1633, Galileo lived on for another 9 years under house arrest. For an elderly and infirm person, house arrest was probably not too unbearable.
And he was still famous and sought out: for example, he was visited in 1638 by John Milton (1608--1674) (Wikipedia: John Milton: Study, poetry, and travel).
Naturally Galileo had to abandon astronomy, but he turned to summarizing his discoveries and developments in physics and engineering.
The resulting book with abbreviated title Two New Sciences had to be smuggled abroad to be published. It was printed in the Netherlands in 1638, by which time Galileo, age 74, had become blind (Wikipedia: Galileo Galilei: Controversy over heliocentrism).
Galileo's physics was only a halfway point to Newtonian physics, but Galileo's approach to practical engineering problems and his concept of work done by machines were more useful to engineers of the 17th century and later centuries than Newton's original formulation of Newtonian physics (Cardwell 1994, p. 97).
Newtonian physics would, of course, eventually be shown to comprehend everything that was correct in Galileo's physics.
Two New Sciences was a book for the future in both theoretical and applied physics. But by implication it also relegated Aristotelian physics and cosmology to history---Samson with a last effort pulling down the temple.
The after-history of Copernicanism?
Well as the 17th century progressed, Copernicanism became more and more accepted as the plausible theory.
In Newtonian physics, which arrived in 1687, heliocentrism is fully explained physically. The planets are in accelerated orbits about a relatively unaccelerated Sun.
Of course, only the Solar System is heliocentric. The universe was seen in the Newtonian system as huge, perhaps infinite, and all the stars are other suns.
After Newton, among the astronomically interested people there were no doubts about heliocentrism.
The Catholic Church accepted heliocentrism as an allowable view in the 18th century.
Newtonian physics also united terrestial and celestial physics ending the two-physical-realms theory of Aristotelian cosmology.
The unification of terrestrial and celestial physics finally made astronomy somewhat experimental.
We can NOT do experiments on stars, galaxies, etc.
But experiments on Earth do reveal aspects of the physics of space.
Our ability to understand the universe was vastly extended until nowadays it is possible we might one day understand the universe completely.
It does show the scientific method in action: the cycle of theory and observation/experiment that yields advance toward truer, more general theories. The scientific method cycle is an upward spiral, not just a circle.
Of course, the history we've gone over not a typical example of the scientific method: it's much too extended in time to be typical.
But at the end with Galileo, Kepler, and other lesser lights, one sees the modern scientific method developing in which physical theories are found adequate or inadequate by testing them against nature, not by seeing how they fit in an overall philosophy of the universe and metaphysics.
The development of the modern scientific method is a main feature, but not the only one of the Scientific Revolution of the 16th century and 17th century.
Philosophy and metaphysics still play a role. But that describing that role is lecture in itself---and one without consensus conclusions.
