John Pazmino
 NYSkies Astronomy Inc
 2012 May 10
    On 2012 May 7 the 'Science and the arts' series of public shows 
presented 'Copernicus: a more perfect universe' at City University 
Graduate Center on Manhattan. I and other NYSkiers regularly take in 
these shows, usually as individuals. On this instance, due to the 
glatt astronomy nature of the show, NYSkies made a social event of it, 
with several of us seeing the show and then doing supper afterwards. 
    The Graduate Center is in the center of Manhattan's corporate 
district, on Fifth Avenue and 34th St, near many transit lines and a 
short walk from Grand Central Terminal, Port of Authority, Penn 
Station. Its talks are almost always completely filled with latecomers 
turned away for want of seats.
    The presentation was done by Dava Sobel, astronomy author of many 
excellent books. She now is trying her skill at writing astronomy 
plays. This Science and the Arts program was a act-out of parts of 
her play in simplified form and with her running commentary. It is 
based on her current book about the Copernicus meeting with Rheticus.
    Science and the Arts engages the theatrical firm 'Break-A-Leg' 
that specializes in a minimalist style of acting. Actors work on bare 
stage with back-curtain dropped and in street clothes. Only a bit of 
styling is used in selecting the contemporary clothing. 
    Props are limited to simple chairs and tables, likely already on 
premises for general use. There is no elaborate scenery or costume. In 
most cases the same dress is worn thruout the production. 
    This format at first looks too schoolish. It is actually 
extraordinarily effective because it focuses the audience on the 
dialog with no distraction from the surrounds. The strength of the 
style is in the dialog among the actors,plus commentary offstage by 
the author. 
    This minimalist style is an excellent method for astronomy centers 
not outfitted for conventional theatrical performances. It may be 
employed on a simple raised stage in an auditorium or at grade-level 
in the front of a classroom. The acting does have to be practiced and 
honed to a professional level. 
The play
    The segments of Sobel's play shown were the meeting of Rheticus 
with Copernicus. Rheticus came from Germany on foot thru dangerous 
territories into Poland. He faced many travel troubles but arrived at 
Copernicus's house in somewhat functional state. 
    Poland was a completely Catholic country, with Copernicus holding 
a higher office, a canon, in the Church. He was aware of his bishop's 
hate of the uprisings against the Church that brewed in other 
countries in Europe. While personally tolerant of other faiths, 
Copernicus did have to heel to his boss's orders. 
    Rheticus converted to the new Lutheran faith, then spreading 
rapidly thru Germany. Poland, fearful of the competitor faith, banned 
Lutherans from its land and was on the lookout for Lutheran intruders. 
If found, they were punished by typical nediaeval methods. 
    Rheticus wanted to learn more about the Copernicus ideas of the 
planetary motions. The 'De revolutionibus' was not published but some 
articles were circulated among astronomers and mathematicians. Due to 
the antagonism among the faiths, Rheticus could not seek a direct 
invite from Copernicus. He came on his own with no advance notice. 
Copernicus found him sleeping on the stoop. 
    The play centered on the dialog between the two men during which 
Copernicus explains the new order of the planets. Copernicus is always 
wary of entertaining Rheticus in his house being that as a Church 
functionary he was supposed to turn the visitor over to the 
authorities. At first he tries to dissuade Rheticus from staying, but 
ends up hiding him in the cellar as a guest. 
    Georg Rheticus was chair of mathematics at the University of 
Wittenberg in present-day Germany. He also was an ardent student of 
astronomy. Copernicus was already well-known, before the promotion of 
the heliocentric theory, as a leading astronomer, mathematician, civic 
administrator, physician. Rheticus just had to meet Copernicus and 
arrived at Copernicus's home in Frauenburg, Poland, in 1539. 
    Rheticus did many works on maths, built mathematical models and 
measuring devices, compiled navigation tables, and calculated planet 
positions. He also worked up horoscopes in astrology, as did pretty 
much all astronomers of the time. 
    Rheticus knew Martin Luther as a colleague at Wittenberg and took 
up his new belief system. He was, like all Lutherans and other 
protestants, persona non grata in Catholic Poland. His trip was always 
threatened by capture and dispatch. 
    He was brought up under the Ptolemaeus system of planets and 
wanted to learn Copernicus's heliocentric model. The Earth-centered 
viewpoint was part of almost all faiths, even Lutherism and others 
protesting against the Church. Under Copernicus's mentoring Rheticus 
came to accept the Sun-centered model.  
    By the later years of Copernicus, Rheticus was compiling and 
editing the 'De revolutionibus' and arranged for its publication in 
Germany. The first copy didn't reach Copernicus until he was dying in 
his bed from a stroke. After seeing the book Copernicus closed his 
eyes and died. 
    Martin Luther, a monk in the Catholic Church, issued in 1517 a 
protest against what he saw as abusive practices. He made a series of 
claims, including the sale of 'indulgences' and apparent discrepancies 
of theology compared to the scriptures. 
    His ideas were taken up by many others who felt abused by the 
local Church authorities and as a unit they broke away into their own 
form of Christianity. In time the faith was named Lutherism or 
    Lutherism is the first major break-away faith system, now being 
the main faith system in Germany, Norway, Sweden, Finland, Denmark. 
There is substantial Lutheran presence in all parts of the world but 
the center is Germany and Scandinavia. 
    Mind that there was no 'Germany' in the 1500s as a consolidated 
nation as yet. There were separate smaller countries which are more or 
less the provinces in modern Germany. 
    Outside Germany other groups split off from the Catholic Church in 
protest, often under the leadership of a specific person. 
Collectively, even among rival factions, these belief systems are 
called protestant faiths and their members are genericly Protestants. 
    Note well that the word is 'proh-TESS-tant', the active 
participle. Over the centuries the accent slided to form 'PRO-tess-
tant' or, a bit sloppily, 'PRO-teh-zant'. 
    The Church was fearful of such insurrections. Poland banished 
Lutherans from its land. Any found were, uh, dealt with sternly. 
    As barbaric as this policy seems today, many faiths protesting 
against the Church engaged in nasty practices. Recall that in the 
American colonies, there were ugly suppressions of alternate beliefs. 
These were carried out by the very people who fleed from faith-based 
persecution in Europe, Even to this 21st century, there are remanents 
of this intolerant mindset in various pockets of the United States. 
Most notable is the faith-based aggression against assorted 
alternative lifestyles. 
    Rheticus notices a large machine like a cabinet or hut and 
inquiries about it. Copernicus dismisses the query but Rheticus 
persists. Copernicus allows Rheticus to climb inside while he, from a 
crank outside, sets the machine to rotate. There is no actual machine 
on stage, but a phantom one that's acted out in mime. 
    Copernicus makes like he's cranking while Rheticus Injun-squats on 
the floor. He squeals in delight at the scene inside the machine. He 
shouts that he's sitting still but the entire machine spins around 
him. He points out a few constellations as they pass around him. The 
cranking gets tiring for Copernicus. He tells Rheticus that time's up. 
    This act in Sobel's play is entirely imaginary, like certain other 
segments later. There never was such a planetarium or other device in 
Copernicus's life. On the other hand one could have been built using 
materials and mechanisms known at the time, after DaVinci. 
    Rheticus asks, after getting out how the whole room could turn so 
smoothly while he was sitting still in the middle. Copernicus explains 
that the hut was stationary on the floor. The seat span around. 
    At first, given the crude state of machinery in the 1500s, this 
seems to be an unlikely achievement. It could be done by mounting the 
seat on a a polished bamboo bearing lubricated by lard. The crank 
could be attached to a spindle under the seat by a leather belt. Since 
the rider has to squat inside, imbalance as the seat started or 
stopped would be masked by the general wobbliness of the posture. 
    The idea of this segment is to demonstrate that motion is 
relative. The sky turns around the Earth because the Earth rotates and 
orbits around the Sun. The sky does not move over a stationary Earth. 
Speed of Earth 
    During the debate about the motion of the Earth,Rheticus asks how 
fast must the ground move to complete one turn per day. Copernicus 
does an in-head calculation, figuring 25,000 'miles' for the Earth's 
circumference and 24 hours in the day. Earth's ground (at the equator) 
must speed around at about 1,000 miles per hour (1,600 KMH). 
    In the 1500s this was a stupendous speed, one that prompts Rheticus 
to argue about the blast of wind this must create, like some extra 
fast ride on a wagon. In the 21st century this is still a humongous 
speed, faster than most airliners travel. Only for a brief period in 
the 1970s-1990s was it surpassed by the Concorde. 
    The use of 'miles' is Sobel's fictitious feature in her play. She 
later explained that she wanted to use some ancient measuring system, 
not current metrics. There really is only one such scheme, the 
oldstyle British units, still familiar in the United States. Poland 
and Germany never employed this scheme. They lived with other peculiar 
units. These would be too obtuse for Americans. 
    Rheticus then asks about the speed of Earth's orbital motion 
around the Sun. Here Copernicus draws a blank because he did not know 
the actual distance of Earth from Sun. If he did, the answer would be 
simply the circumference of that orbit divided by 8,766 hours, the 
number of hours in one year (including the 1/4 fractional day). 
    Today we know that speed as 30 KMS (not KMH). In the De 
Revolutionibus Copernicus does offer a radius for the Earth's orbit of 
1,000 Earth radii (rounded), this being some 6,400,000 kilometers. I 
forget where he got this figure but it is close to the Aristarchus 
value of 1,200 times Earth's radius. 
    Using this grossly too-small value we have the orbital speed of 
Earth as 1.29 KPS or 4,620 KMH. These would be insanely humongous 
speeds for the 1500s mind to comprehend. They were not achieved by 
humna flight until the Space Age. 
Large and small Earth 
    Note that Copernicus accepts the 'large Earth' school, claiming 
the Earth to be 40,000km circumference. The 'small Earth' school 
argued for a 25,000km circumference. The disparity came from disputes 
in measuring the linear length of angular arcs, a situation not 
resolved until the mid 1600s. 
    The two factions in the late 1400s competed for the feasibility of 
sailing from Europe to China via Atlantic Ocean. It was just possible 
to build and kit out a ship to last the journey (in ignorance of the 
Americas) for the smaller circumference. This was Columbus's thesis 
for soliciting support for his trip. 
    It was beyond possibility for the larger circumference. The ship 
would fall apart from want of repairs and the crew would die from want 
to food and drink. In the open ocean there would be no ports for 
replenishing the ship and crew. 
    Columbus was as lucky as hell that when his ship was almost 
exhausted of supplies and provisions, he hit land in the Caribbean 
Sea. This land by great fortune is where China would be for the 
smaller Earth. Columbus thought he was in the Indies, the islands 
dotting thee Pacific Ocean near China. To this day we the Caribbean 
islands are called the West Indies, preserving their initial identity 
with the Indies (now East Indies) near China. 
    If there was no American continent but only a vast Atlantic Ocean 
on the larger world, the voyage -- the one and only one! -- of 
Columbus would be but a footnote in history. Europe would probably 
have never again considered a westward trip to China until the era of 
steamships in the 19th century. 
Attachment of the air 
    Rheticus argues that if the Earth moved the air would slip away, 
causing massive winds. Copernicus replies that the air is attached to 
the Earth and moves along with her. He's at a loss to explain why or 
how the air, so tenuous a substance, can adhaere to the ground but 
he's sure in his heart it must. 
    Rheticus had a convincing argument. If you on a wagon hold a 
candle and then move forward, the smoke and flame drift backward, In 
the real sky clouds move about over the ground under the push of winds 
with no regard to a gross movement of the Earth. The quiet behavior of 
the air, having only local motions, is evidence for a stable Earth. 
    Copernicus has no solid basis to elaborate why the air stays with 
the Earth. He merely repeats the assertion again to Rheticus. 
    As late as the mid 1000s the behavior of the air was not well 
appreciated. One of Verne's stories explained how a balloon allowed 
his heros to escape from a comet. They waited until the comet came 
close enough to Earth to join their atmospheres. The balloon then was 
steered thru the united air to land safely back on Earth. 
Relative motion 
    Rheticus asks how the Earth can be moving around the Sun if he 
feels nothing of its movement. On a horse he feels the bumps and jolts 
under him and feels the air blowing against him and sees the scenery 
slide backward. Copernicus tries to describe the feeling on a ship 
gliding on a smooth water. Inside the ship there is no feeling of 
    This is also an imaginary scene in the play. The concept of 
relative motion, with this example from Galileo's 'Dialogues', just 
wasn't in place for Copernicus. Nor was the concept of inertia, mass, 
force. The lack of firm understanding of these principles hindered 
Copernicus's theory of the solar system. 
    The Galileo demonstration was elegant. He postulates a ship with 
no windows to refer to the outside scene. In it the rider has several 
experiments while the ship is gliding over still calm water. 
    I don't recall rightly but the rider has such things as a jar of 
bugs, a candle, a ball, some kind of toy. The bugs are released and 
they fly around the room exactly as if they were on solid ground. The 
candle flame and smoke drift upward as they do on stable ground. A 
game of ball plays the same as on land. The toy works the same way on 
the ship as on land. 
    Galileo concludes that the behavior of natural events is the same 
regardless of the relative motion of the observer's platform (the ship 
in this case) against another platform (the land). By this argument he 
allows that the Earth can move, like the ship, within the outer frame 
of the stars and Sun, as in the Copernicus model of the solar system. 
    This was not proof of the heliocentric theory but merely evidence 
that it could be valid. It is a mistake some simple accounts of 
Galileo make that he proved the Earth orbited the Sun. He didn't and 
he couldn't. He gathered observations and experiments, crucial ones, 
to show that the heliocentric system is plausible. His own faith in it 
made him state it was an actuality. 
    This, the Galileo Principle, 300 years later became the foundation 
of Einstein's theory of relativity. In more concise form, all the 
behaviors of nature operate the same for all observers, regardless of 
their motions relative to each other. 
    One of the behaviors of nature is the speed of light. This is 
derived from physical properties and laws and not by a mechanical 
measurement. As a behavior of nature it is the same for all observers. 
The Sun as center
    Copernicus had no way to put forth a physical reason to place the 
planets around the Sun. The nature of the SUn was thoroly unfathomable 
and there was no concept of attraction, force, gravity. He put out 
soft arguments about the Sun being the most glorious of the orbs. He 
was the body that shines light and heat on Earth, making the existence 
of life possible on Earth. 
    He mixed in some belief features about the Sun shining his glory 
like God and how we circle around God. Stuff like that. Hardly the 
making of good science, but there was little enough good science in 
the Renaissance to all short of.
    Why should the Earth move at all rather than let the Sun and his 
retinue of planets, and the stars circle Earth? COpernicus notes that 
under his scheme the stars had to be immensely far away in order that 
they still remain 'fixed stars' to observation. The stars, the 
celestial sphere was simply 'too big and heavy' to do the moving. 
    Apart from Sobel's show the De Revolutionibus explains this point. 
Copernicus states the size of the solar system where the Sun is 1,000 
times (rounded) farther away than the Earth's radius, Saturn is 10,000 
times Earth's radius from the Sun, and the stars must be perhaps 
100,000 times the Earth's radius away. Such immense a world could not 
turn around the Earth. 
    Rheticus pleads that the Copernicus world has so much wasted space 
between planets, orders and orders bigger than the whole Earth. The 
geocentric world nests the planets in closely fitting shells. 
Copernicus has no strong response but again appeals to the grandeur of 
God and the majesty of His creation. 
    Copernicus was skating on thin ice. With the threat of protests in 
Poland the Church wasn't eager to take in new ideas outside the power 
structure of the day. The scriptures speak of the heavens going around 
the Earth, never minding that this could mean an apparent or relative 
motion. It's best that the scriptures be taken as are than open them 
to invasion by alternative beliefs. 
    Copernicus had to cool it, being himself part of the Church. He 
had some supporters but far too many opponents to come out in public 
with his heliocentric system. 
    As it happened, he was in his death bed when the first complete 
copy of De Revolutionibus was placed in his hands. He probably didn't 
notice that, altho printed in Germany, the book had a preface added by 
the local protesters that declaimed the actuality of a Sun-centered 
world. Even Protestants were leery of, erm, revolutionary thoughts. 
    It can be a shock to modern newcomers into the astronomy 
profession to discover that many of their ancestral fellows did 
astrology. In the 1500s there was still a general acceptance of 
astrology as part of astronomy, or the other way round. 
    The times were such that astrology was an odium to be tolerated by 
astronomers, partly as a means of subsistence. People pay to get a 
fortune reading but not for learning where Mars is in the sky. And the 
amount earned thru astronomy lectures and shows was too infrequent and 
inconsistent to build a livelihood on. 
    One aim of astronomy at that time was to refine the calculation of 
planet positions by tweaking the Ptolemaeus model. The value for an 
excentricity was adjusted, so was the longitude of a perigee, and so 
on. Some of these fixes were caused by real mutation of the orbits 
over the centuries, a fact not realized by the Mediaeval and 
Renaissance astronomer. He thought the revision was the result of more 
and better observations or errors in previous determinations. 
    Rheticus and Copernicus discuss astrology as a casual part of 
their careers. Copernicus notes that his heliocentric model yields 
more accurate planet positions for that purpose. 
De Revolutionibus Orbium Celestium 
    Copernicus's book translates as 'Concerning the revolutions of the 
celestial orbs'. The parsing is preposition 'De', ablative plural of 
'revolutio', genitive plural of 'orbis', genitive plural of 
'celestis'. Some negligent authors call the book '...bus Orbitum 
Cel...', perhaps by thinking of orbits. 
    The word 'revolution' refers to the circulation of the planets. 
Because the book caused a mass change of human thought and collateral 
social and political change, the word came be mean 'sudden forceful 
change'. Our use of the word brings up insurrection, civil uprising, 
overthrow of rulers, and similar, ahem. revolutions. 
    De Revolutionibus was written originally in Latin, the language of 
the time for scholarly works. It's available today in Latin and many 
other languages. English translations are plentiful in both print for 
pay and download for free. 
    It really is a valuable exercise to read the Latin work, taken 
from a large library in modern reprint, to properly take in the mind 
of Copernicus. I realize Latin is not any where so common a language 
in American schools, but astronomers commonly study it on their own. 
    The book is large and heavy, causing many early students to wonder 
why it's any better than the Ptolemaeus method of working the 
planetary motions. The maths are about as convoluted for both 
geocentric and heliocentric models and the results seem about equally 
good when compared with the sky. 
    Copernicus made two major breakthrus in maths, explained in an 
early part of the book. First, he employs the Hindu notation of 
numbers, what we call Arabic, rather than the Roman number scheme. 
This immediately eased the chore of doing even simple maths if you 
ever tried doing long division with Roman numbers. (Go ahead, try it.) 
    He also switched to decimal notation, also from the Hindu world, 
setting aside the base-60 system. This, too, vastly simplified the 
maths. In fact, the change to Arabic and base-10 numbers arguably 
saved De Revolutionibus from regressing into neglect. 
    It also is easier for us astronomers today to walk thru the book 
with modern calculettes. In the Sobel show, neither point of maths was 
made in the presented segments of the full play. 
    Unlike the Ptolemaeus method, the Copernicus method explicitly 
includes the Sun in the computation of planet positions. The Sun's 
motion was buried in Ptolemaeus, not put out in front as a direct part 
of the work. In essence, you calculate the planet position relative to 
the Sun and then the Earth's position relative to Sun. The combination 
of the two yields the place of the planet relative to Earth. 
    Because the Sun's location, for a run of several planet calcs need 
be done once for the whole run, already the maths are simplfied. Under 
Ptolemaeus each planet needed its own peculiar computation. The parts 
involving the Sun were there but hidden. 
Some Copernicus premises 
    In spite of Copernicus's sea change in perspective for the solar 
system he held to a few ancient principles. These got hi into massive 
troubles with the planet calculations, so much so that many opponents 
questioned the need for the heliocentric model. 
    He insisted that all motion be uniform circular motion, constant 
angular speed around a center. The center of motion did not have to be 
the center of the circular path of the planet. Ptolemaeus made this 
premise, too, to build his scheme. Copernicus, to duplicate the actual 
path n the sky, mounted small circle on large circles and shifted 
centers of motion from geometric centers of circles, much as 
Ptolemaeus did. 
    Copernicus also insisted that the orbits of the planets be all in 
the same plane, a flat plate of rings, around the Sun. Planets in 
coplanar orbits would travel in the ecliptic. They don't. They wander 
north and south in ecliptic latitude. 
    Both Ptolemaeus and Copernicus employ subsidiary circles mounted 
on the main orbit to waggle and wobble to shift the planet's latitude. 
    Copernicus banked his calculations off of the mean Sun. It was 
usual to smooth out the irregular movement of the Sun by posting a 
phantom Sun that travels at a uniform speed thru the zodiac. The real 
Sun moves a bit faster in northern winter and a bit slower in northern 
summer. Stating positions relative to the phantom Sun made it harder 
to relate the computations to the sky. A secondary worksheet was 
needed to correct the planet to ride on the real Sun. 
    This is a superfluous exercise today but because the character of 
the Sun was unknown, it could have been a ball of aethereal light. It 
seemed natural to leave it alone and work with a better behaved mean 
Sun, a geometric point that didn't shine. 
    Kepler first demonstrated that the planet orbits are rooted on the 
globe of the Sun. Once he did this, in his Law #0, or #1a, Kepler 
broke open the way for a vastly easier and quicker method of 
calculating planet motions and positions. 
    One interesting point sometimes asserted is that Copernicus 
predicted the phases of Venus. He didn't in the De Revolutionibus.     
It is true that by letting Venus be a globe like Earth it would 
display the Galileo pattern of phases as it rounds the Sun. 
    It would be dicey for Copernicus to banner this prediction. It was 
impossible to test without the telescope, not even with daVinci's 
foggy blurry lens. It would be lousy science for a Renaissance 
gentleman, must more so for a fellow of civic authority. 
    Maybe he did so in a private letter or article, but curiously the 
story didn't come out until long after Galileo found the Venus phases 
by telescope. Copernicus seems to say nothing about the nature of the 
planets. The planets while philosophicly worlds like Earth with Earth 
being now the third of these worlds from the Sun, they could just as 
well remain insubstantial points of light. 
Spheres of the planets 
    In the prevailing model of the Earth-centered universe it was 
natural that the planets and stars circulate around the Earth. Thee 
was no need of a deeper explanation. 
    One spinoff of this geocentric model ws the lack of external means 
to set the sequence of the planets upward from Earth. In which sphere 
or shell or ring did each planet run? This was a probelem for 
Prolemaeus, who confessed that there was no objective way to tell the 
height of each planet above Earth. They all looked like points or 
discs of invariant aspect no matter where on Earth they were viewed 
from. They displayed no parallax to form a surveying triangle on them. 
    Ptolemaeus allowed a traditional, for Greek times, order largely 
based on the angular speed of each planet thru the zodiac. The Moon 
was obviously the fastest, rounding the zodiac in 27 days. She also 
was the only planet that altered shape, being mutable like the earthly 
world. She must be closest to Earth at the lowest elevation. 
    In fact, she distance from Earth was actually triangulated to be 
about 60 Earth radii away, a figure that by the stroke of luck is the 
base of the maths system of the era, base-60. Where we say a radius is 
one, or 10 or 100, unit, the Greek said it was 60 units. 
    The Sun passed thru the zodiac in, uh, one year, Mars in about 
two, Jupiter in 12, Saturn in 29. So far so good. Sun, Mars, Jupiter, 
Saturn stacked up over the Moon in that order. Saturn was up against 
the sphere of the fixed stars. 
    Mercury and Venus were a problem. Over the long term they 
circulated thru the zodiac in one year pacing the Sun. Unknown to 
Prolemaeus and all time until Copernicus, these planets are tied to 
the Sun and are dragged around the zodiac with him. 
    Mercury whacked around form morning to evening and back in 4 
months while it took Venus about 19 months to do the same. Let's put 
Mercury next above the Moon, then Venus, Sun, and the other planets. 
    Some astronomers figured differently and put the order as Moon, 
Venus, Mercury, Sun, &c. There were over the millennia pitched battles 
over the due and proper location of Mercury and Venus. 
    As history fell out, the Moon-Mercury-Venus-Sun order is used to 
assign the names to our days of the week. With Venus the lower, the 
days would have a different sequence of names. Because the week of 
seven days in the current order was a fixture of human society for 
many millennia, there is no hope of ever altering it. We must keep the 
Ptolemaeus order of planets in the geocentric model for ever more. 
Solar system
    The core of the Copernicus model was the creation of a true solar 
system, a unified mechanism that somehow held the planets in orbit 
around the Sun. He had no notion of what the force was to keep the 
orbits intact. The whole pwah of 'force' and all that was missing from 
human thought in the 1500s. Not even magnetism, coming into use for 
the marine compass, was associated with the Sun. 
    By placing the planets around the Sun Copernicus found that the 
sizes of the orbits fell into fixed steps. Mercury had to be closest 
to the Sun about 4/10 the size of Earth's orbit. Saturn had to be 
farthest out, some 10 times the Earth's orbit radius from the Sun. No 
arbitrary scheme of orbits worked. The motions of the planets thru the 
zodiac plus the centering on the Sun forced not only the sequence of 
the orbits but the relative sizes. 
    This brings up the illustration so often shown from De 
Revolutionibus. It's the solar system with neatly compacted nested 
orbits centered on the Sun. Each planet is equispaced outward from the 
Sun with lordly Latin captions. This is nothing but an illustration! 
It does not propose to show the correct spacing of the planets. 
Diagrams further in the book are drawn to correct scale, with 
explanation for their construction. 
    Only a few parts of the full play were presented at this show. 
They were enough to spawn many questions for Sobel, with many coming 
from the NYSkies delegation. She noted parts that were purely artistic 
freedom in order to enhance the tuitional value of the play. There was 
no such planetarium machine and there ws no such deliberate idea of 
relative motion and force. 
    She explained about Kepler alluding to magnets in the Sun, banking 
of the current work of William Gilbert in 'De magnete'. That was many 
decades in the future. 
    After the show let out, Sobel did a book signing for the 
Copernicus book. Many audience purchased a copy for her autograph. The 
NYSkies party went to Brendan's restaurant, a block away, for a 
lengthy supper and free-flowing chat about Copernicus, astronomy, 
science, and other sundry topics. 
    This Dava Sobel event is the paenultimate one in the 2011-2012 
running of Science and the Arts. The next season starts in October 
2012. While most shows are not stricta mente related to astronomy, all 
are of instructive value for any City astronomer. The events are 
listed in NYC Events for each month during the series.