I just know that the earth is the centre of the universe, why do you believe otherwise?

OH, sorry, that's not what I wanted to ask .

Why is Copernicus presented as the guy proposing heliocentrism when the idea is as old as the ancient Greeks, and I've seen textbooks from the year 900 IIRC, in which it is clearly stated that the current mainstream idea was heliocentrism? (the book even states as a sidenote that "some scientists like to think of themselves as the centre of the Universe" ) Was there a fall of th heliocentric idea somewhere between 900 and copernicus?

EDIT: I must have remembered the date wrong. The book was hand written, but quite easy to read for me. It must have been a lot more recent that 900, so it might very well be from copernicus' age. That would explain things of course.

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I believe the Greek Aristarchus around 270BC proposed heliocentrism first, but his acutal works did not survive. We learn of his work through others. He calculated that the sun was larger than the earth and, apparently, reasoned we would be more affected by it than it would be by us.

However, if the Earth moved around the sun, then the stars would appear to shift (parallax), and no shift was seen. [I don't know if the Greeks, however, took the time to look.] Regardless, Artistotle liked Geocentrism and was able to argue convincingly.

Copernicus, in his book, gave reason against Ptolemy's model such as the lack of changes in the appearance of Venus though its Ptolemaic epicycle dramatically changes its relative location to us. He also realized that the orbital periods were proportional to their distance from the sun if the sun were the center.

Copernicus, I think, was greatly encouraged by what he found from the Greeks as he was fluid in their language and even translated at least one book into Polish (supposedly the first one to do so). He cited numerous Greeks in his book that favored a sun-centered universe, too.

It was also a bit gutsy to go against geocentrism when it had become so integrated with religion and at a time of significant religious turmoil, too.

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The date is definitely wrong. Heliocentrism didn't even come into the fore until the 1600s.

While some ancient philosophers were proponents of heliocentrism, they were in the minority. There was just not enough evidence, at that time, to prefer heliocentrism over geocentrism. Occam's Razor led most people to prefer geocentrism, the simplest model, from their point of view.

The merit of Copernicus was twofold. He was the first to suggest that the geocentric model (which had begun to give inaccurate predictions) might have to be dropped and replaced with something entirely different, rather than just tweaked (as previous authors had been doing). And he was also able to construct mathematically a new model that offered an alternative to geocentrism. He was a great observer and measurer of the night sky and mathematician.

But it should be added that Copernicus did not solve the matter. For his model to work, he had to add some modifications which made it arguably as awkward as Ptolemy's model. The orbits that Copernicus proposed for the planets were not simple circles centered on the Sun (that would not have agreed with observational data). Some have even claimed that the predictions his model gave were not as accurate as those given by the modified Ptolemaic model used in his day. Still, it got people thinking about alternatives.

The next attack on geocentrism was due to Galileo, who, using the telescope to observe the sky, made observations which refuted the Ptolemaic model as it was traditionally interpreted. For example, medieval wisdom claimed the planets, the Sun and the Moon were perfect spheres, but Galileo was able to see craters on the moon. And when he discovered that Jupiter had moons, that made the possibility that Earth was not the centre of everything more plausible.

Meanwhile, Tycho had made more accurate measurements than ever before, which confirmed that the geocentric model did not fit the data. He proposed a modified, but still geocentric model to replace Ptolemy's, in which the Sun and the Moon orbited the Earth, while all other planets orbited the Sun.

The final and decisive blow, however, was dealt by Tycho's pupil Kepler. He came up with a heliocentric model of the solar system which fit the data and was quite simple, when he discovered that the orbits of the planets were not circles, but ellipses.

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Yeah the date must be off a lot. 900 would not also mean setting back the written dutch language by 200 years, it would also make it ar more comphensively. It must be one of the later hand written books, I assume somewhere shortly before printig took of. End 1500's maybe? That would explain the recognizable Dutch.

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What's odd about this is that the distance to Venus varies more in Copernicus' model than in Ptolemy's. Did he fold in the phase variations as well in his calculation of brightness variation?Not directly proportional, proportional to distance to the 3/2 power. And it is Kepler who is credited with this, so surely Copernicus must not have had anything so precise. The problem with something imprecise, though, is that the average distance to the Sun is the same as the average distance to the Earth, so I'm not clear on what Copernicus could have been saying there.
That's very ironic, because his idea ultimately ushered in the end of the Renaissance-- the end of the reverence to Greek knowledge.

You can look at it that way, but I think that's too harsh. The Greek attitude of observation, quantification and rationality was surely what mattered, no?

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

Indeed, we continue to sustain the Greek's respect for human intellect, I just meant that in the Renaissance, the Greek's knowledge itself was what was revered. This was an example of deference to authority, rather than what we value today-- questioning via application of the scientific method. Thus it is no coincidence that Galileo, the man sometimes called the "father of the scientific method" (and yeah, that is unnecessarily harsh to the Greeks), was the one who put the final nail in the coffin of Greek geocentrism. So I would say that the ancient Greeks had a complex relationship with the scientific method-- a lot of what they did was excellent science, some was pretty bad science, and it was the scientific method that ultimately replaced almost all of their thinking about the universe. But you are right that we all have this uneasy relationship with science-- how much of today's scientific thinking will ultimately also be replaced by application of that very same method? It's kind of a double-edged sword that way.

That seems to be the case. I have both books and neither offer a nice dimensional drawing that makes their model easy to understand.

Surprisingly, a U. Texas computer model using the Ptolemaic system helped refine his model and reduced it down to 9 or so circles total, and with accurate results.

Yes, IIRC, he did use circles but included epicycles. However, he eliminated Ptolemy's equant (center points for each planet). Copernicus, it has been said, felt there should be just one center and not mulitiple centers.

So far I have not found reference to phase variations, but you'd think that would have to be an issue.

To add some spice to the mix, it was Ossiander - the one people critisize for watering down this masterpiece by saying it was an hypothesis in lieu of a claim on reality - who first mentioned it in his preface of Revolutionibus:

The calculations are easy and the variation turns out to be slightly more than a 16x area increase.

But notice the colorful grammar for someone who is offering this as a hypothesis. I wonder how many of these colorful cats would get canned around here. [Not that we wouldn't tame them first, of course.]

Yes, and he did not use the porportionality term. I forget his phrasing. The key is the elegant harmony of a model which has a single center (slightly offset from the sun, sun; heliostatic, I think is the term) and a correlation between the sequence of the planetary orbits where their periods increase in the same sequential order (the most inner is the fasted, the outer most is the slowest, etc.)

Yes. Someone should start an irony thread for scientific history.

It does make sense as this was the first time that mankind seemed to be able to feel comfortable in being at, or above, the level of the Greeks. We finally moved on from there.

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But my point is that Copernicus' model has Venus going from 0.3 AU to 1.7 AU from Earth, which is a factor of about 32 in "the body"! (Granted, you couldn't see the whole of this, but that is also true for Ptolemy.) Also, you don't actually see the face of Venus, only the amount that is sunlit, so that complicates matters as we both recognize but Copernicus apparently did not.
I see what you mean, yes it is interesting that Copernicus noticed that, I hadn't realized that was part of his argument.

I still disagree with that characterisation of the Renaissance. There was a lot of reverence for Antiquity, to be sure (which there also was, in a more moderate way, during much of the Middle Ages), but there was also the desire to improve on it, which sometimes led to questioning ancient authors.

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

Did people have accurate estimates of the size of Venus in the time of Copernicus? (I'm assuming the planet's size affects your proposition.)

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

I am no Renaissance scholar, but I had heard that the "rebirth" was really the rebirth of understanding of what the Greeks knew. That is, most of science during the Renaissance was devoted to re-discovering what the Greeks already thought they had figured out, so that "scientific research" basically entailed reading Greek or Latin. Were there any significant scientific discoveries of their own that happened during that period? Until the invention of the telescope, that is, which pulled out the whole house of cards.

No, the apparent size itself doesn't matter-- these are just how it would scale with distance.

Copernicus "sold" people on an idea that had been definitely "against the mainstream."

Also, he added the force of mathematics to the issue. While his numbers did not quite add up, because he assumed circles instead of ellipses, one is hard-pressed to argue with his math.

I think that's why he gets the credit for the idea...even though it was not 100% original.

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It was a complex and gradual process. A rebirth of ancient culture, as you say, but at first that meant the culture of late Christian Antiquity; of Tertullian, Augustine, and Constantine. The popular image of a Renaissance man turning his back on the Middle Ages and trying to rebuild the world of Cicero, Livy and Augustus is generally not correct. As it progressed, however, the Renaissance became bolder, more classicist, and more secular.

I think there were several inventions (like mechanical clocks) or popularisations of new technology (the windmill, gunpowder, the lateen sail) in Europe even before the start of the Renaissance, though I can't think of anything as spectacular as what followed. The printing press appeared during the Renaissance. There were also the voyages of the Iberians, which challenged the world view of influential ancient cartographers.

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

All right, I'll accept that more accurate description, but I think it still holds up the same points I was making above.
But these are all engineering triumphs, not triumphs of challenging authority. They required intellect and courage and hard work, but no revolutions of thought except changing some maps that had forgotten what the Greeks already knew-- that the Earth was a sphere about 40,000 km in circumference.

Some influential ancient cartographers said there was land all around the Atlantic. Others claimed the equator was so hot that humans could not survive there. Ancient sources were not consistent, and the most famous were not always the most accurate. During the 15th century (as the Renaissance was starting, though these things can never be pinned down), Iberian sailors tested the limits of ancient geographical knowledge. The voyage of Columbus, at the end of that century, seems to show rather eloquently that, while Renaissance scholars and policymakers were acquainted with many of the classical geographical treatises, they did not take them as gospel. I think that's the beginning of experimentation and skepticism.

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

Ironically the rediscovery of the classical scientific writings - aristotle, ptolomey, galen, etc.,- had occurred much earlier, in the 12th and 13th century. The so-called renaissance was marked more by the setting aside the authority of the classical writings - ptolomey's cosmology, aristotle's physics, galen's medicine, etc. This was protracted process - aristotle was not finally supplanted as an authority in biology until the 18th century.

So you have the classical writers being regarded as authoritive in western Europe fromthe 12th-18th century and a "renaissance" that last from the 14th-18th century. Given the significant advances in science and technology that happened in the mediaevel period, the whole "renaissance" as a discrete epoch becomes something of an illusion, albeit one convenient for a number of purposes.

Jon

The Renaissance was a very real period in art (no one in Europe was imitating ancient styles in the 12th or the 13th century). I accept that it may not be a very useful concept in other branches of history.

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

Yes, art is another matter. The Renaissance was certainly many things to many people, and indeed very little at all to the "common person" at the time.

Yes. I don't have a great answer for you, but I am interested in finding one. Perhaps the glare in superior conjunction would help, but that would be true for both models.

The 16x variation comes from their knowledge of the ~40 deg. elongation. In such a case, difference between perigee and apogee (Ptolemy) would be 4x (unless I am "ignorant of geometry" [ ]).

I calculate that a 40 deg. elongation would produce a distance variation of ~ 4.6x (or 21x in apparent size for an object that has no apparent size. )

Its true elongation is 47.8 which produces a 6.7x distance variation, thus a 49x apparent size change.

This ignores the little problem with observing during a superior conjuction, of course.

If there is time tonight, this will get explored further.

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For some reason, I want to say the Greeks were primarily rediscovered by Europeans thanks to certain earlier conquests. Is this way off?

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That's the story I've heard.

While in Jerusalem and the surrounding lands, many European leaders came across the writings of the Greeks that the Arab scholars had copied. They also discovered the old trade routes of the East. Italy became very rich. The Portuguese decided that maybe if they could find an all water route around Africa, they could take home those riches for themselves.

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Thanks, that's what I understood.

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The apparent size of Venus is just too small for unaided human eyes to resolve it (yes, yes, in theory, young persons will excellent eyesight might distinguish it from a nearby true point source of the same apparent brightness, but that's not a real-world situation). Therefore, neither the Greeks nor the Arabs nor Copernicus could test one hypothesis against another by using the apparent sizes of the planets.

Nor is it possible to test the different models using the apparent brightness of Venus, in particular, due to the changing phase, and the lack of good standard light sources which would serve as comparisons over the period of weeks which are required to see significant changes in the light of Venus.

The one observational test that the Greeks could have, and should have, done -- was the change in the apparent size of the Moon due to its motion on its epicycle. As far as I know, we have no record of any astronomer looking for the very easily noticed changes in its apparent size ...

Can anyone contradict this claim?

I don't think that's true, it sounds to me like you are talking about the end of the Renaissance. As I heard it, the Renaissance ends along with the "love affair" with classical wisdom, an end pretty much ushered in by Kepler and Galileo (this is the scientific perspective, I can't speak for the arts).
The Renaissance is over by the 17th century, those are the days of Galileo and Newton, and the next generation of scientific discovery. I also used to think that the "rebirth" included the discoveries of Galileo and Newton, ushering in the "golden age" of science (that is arguably still here today), but I later learned that this is the "modern era", not the Renaissance. It was really the rebirth of classical wisdom, not the birth of new wisdom.

Yes, I meant in the mathematical sense and which is why I stated it was an object that has no apparent size. Yet, this "apparent size" would alter its apparent magnitude which would be noticeable and testable. [Ken actually addressed both in his earlier response to me.]

Since the app. mag. of Venus changes less than 1 mag., I would assume they would believe a 16x gain in app. size should reflect a greater visual mag. difference.

[Now that I have the book in hand... it was remarked by Ossiander that the elongation was greater than 40 deg. Thus, at 40 deg., the brightness would change due to a 21x gain in overall apparent size, less the portion that could not be observerd due to the glare of conjunction. So, 16x seems reasonable with these assumptions, I suppose.]

What I did not recall was if phases were part of their consideration. Considering the Moon's example, how could they not? The Moon also allowed them to consider whether or not they glowed or were reflecting bodies.

In Chapter 10 of Book 1, Copernicus addresses both the above.

"Accordingly, all the followers of Plato suppose that all the planets - which are otherwise dark bodies - shine with light received from the sun, they think that if the planets were below the sun, they would on acount of ther slight distance from the sun be viewed as only half - or at any rate as only partly - sperhical.", and then he says, "as we see in the case of the new moon or the old".

Ken, this chapter touches on the area regarding the commonality of matching the sequence of orbits with periods. Apparently, they all held the nice relationship for the outer three (Mars, Jupiter, Saturn) but there were problems for the inner two. Some (ancient philosophers) argued Mercury and Venus were between us and the sun ("below"), and others argued their orbits were beyond ("above") the sun. This would bust the harmony of the orbit/period correlation, no doubt.

On this issue, the argument for the outer (beyond the sun) was favored by the ancients because of the lack of noticeable solar magnitude variation, due to transiting ("interposition"). [1639 was the first transit observation, thanks to the telescope.]

Naturally, the other camp has its share of arguments. The "belowers" posit that there is just too much empty space between earth and the sun if the "abovers" are correct. As for the lack of solar mag. change during transit, well, that is due to their idea that they glow and are not reflective bodies (just when phases were starting to look good).

I would bet you are right considering their lack of experimental interests. Gribbin's The Scientists (I think this is the one, and now a bargain book at B&N), claims that Copernicus used this as a strong argument against Ptolemy, but I have yet to find it.

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As I recall a lot of the classic texts, Aristotle in particular, were translated from Arabic into Latin during and after the Moorish period in Spain.

Jon

That is also my understanding. The fall of Constantinople, I have read, precipitated much of the renewal of Greek works.

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Lighten up! This is a stellar board!

Frankly, I think there's a lot of nonsense and waffling regarding the return of the works of classical authors to Western Europe. Different historians will tell you that classical culture was recovered thanks to:

- the fall of Constantinople;
- the Crusades;
- the Arabic presence in Iberia;
- Charlemagne;
- the Beneditines;
- Irish monasticism;
- etc., etc., etc.; take your pick

Here's what I've gathered: many of the classical works were available in Western Europe throughout the Middle Ages (a few did disappear). They just weren't read, in most cases. People had other priorities, like feeding their children, surviving epidemics, escaping from barbarians, or saving their souls. After the turn of the millennium, when the political and demographic conditions calmed down in Western Europe, they slowly began to dust off those old books, read them, and think about what they said. That initiated a long process which would eventually lead to the Industrial Revolution. As far as science, knowledge, and technology are concerned, there was no sharp interruption between the 1000s and the 1900s in Western Europe.

I didn't think the Moon was supposed to have epicycles in Ptolemy's model...

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.