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Fixed Stars: Ptolemy vs Ulugh Beg/Regiomontanus?
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Mark
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Posted: Mon Mar 01, 2010 2:42 am    Post subject: Reply with quote

Quote:
is it not a fact meanwhile that the declaration of the fixed star positions by Ptolemy was erroneous?


Despite his undeniable achievements it was inevitable that Ptolemy's ideas set out in the Almagest would lead to some astronomical errors. This is because Ptolemy (and anyone following him) was operating under a number of incorrect astronomical assumptions in the Almagest. In summary these were:

1 He assumed the rate of procession was 1 degree per century. We now know the rate is approximately 1 degree every 72 years.

2 Ptolemy stated that the inclination of the Earth's axis is 23'51 whereas in reality we now know it is 23'30.

3 Ptolemy stated that the apogee of the Sun was fixed at around 5'30 Gemini. We now know the apogee of the Sun is not fixed at all.

However, Brady's statement above that astrologers would have just been adding on degrees to Ptolemy's star catalogue until the work of Ulugh Beg and Regiomonus appeared is historically incorrect. By the mid 9th century Islamic astronomers had completely overturned Ptolemy's assumptions and produced a far more accurate astronomical model. Contrary to what many believe Islamic thought did not passively accept Ptolemy's ideas in the Almagest the way Hellenistic and Roman astronomers had.

In particular early 9th Century Islamic astronomers:

1 Calculated the rate of procession to be 1 degree every 66 years which is much closer to the modern figure.

2 They calculated the inclination of the Earth's axis to to be 23'35. This is extremely close to the modern figure calculated at 23'30.

3 They recalculated the apogee of the Sun and found it was actually moving rather than fixed.

Following these reforms the 10th century Persian astromomer Abd al-Rahman al-Sufi recalculated the position of the fixed stars in his 'Book of Fixed Stars' published in 964.

http://en.wikipedia.org/wiki/Abd_al-Rahman_al-Sufi

http://en.wikipedia.org/wiki/Book_of_Fixed_Stars

As the book was published in Arabic it would have been widely disseminated across the Islamic World and therefore available to astrologers. However, it seems it may never have made its way to Europe as it does not appear to be a source available to the 16th century European astronomers.

Despite this , earlier reformist Islamic astronomical work did have a strong impact on European thinking. For example, the 9th century astronomer Muhammad ibn Jābir al-Harrānī al-Battānī produced astronomical tables and important astronomical research in a work known as the Zij. This work was a primary influence on Islamic and Jewish astronomers compiling the Alfonsine tables produced in Toledo, for King Alfonso X of Castile in the 13th century. Later this work of al-Battānī heavily influenced European astronomers like Tycho Brahe, Johannes Kepler, and Nicholas Copernicus.

From Wikipedia:

Quote:
Al Battani worked in Syria, at ar-Raqqah and at Damascus, where he died. He was able to correct some of Ptolemy's results and compiled new tables of the Sun and Moon, long accepted as authoritative, discovered the movement of the Sun's apogee, treated the division of the celestial sphere, and introduced, probably independently of the 5th century Indian astronomer Aryabhata, the use of sines in calculation, and partially that of tangents, forming the basis of modern trigonometry. He also calculated the values for the precession of the equinoxes (54.5" per year, or 1 in 66 years) and the inclination of Earth's axis (23 35'). He used a uniform rate for precession in his tables, choosing not to adopt the theory of trepidation attributed to his colleague Thabit ibn Qurra.

His most important work is his zij, or set of astronomical tables, known as al-Zīj al-Sābī with 57 chapters, which by way of Latin translation as De Motu Stellarum by Plato Tiburtinus (Plato of Tivoli) in 1116 (printed 1537 by Melanchthon, annotated by Regiomontanus), had great influence on European astronomy. The zij is based on Ptolemy's theory, showing little Indian influence. A reprint appeared at Bologna in 1645. Plato's original manuscript is preserved at the Vatican; and the Escorial Library possesses in manuscript a treatise by Al Battani on astronomical chronology.

During his observations for his improved tables of the Sun and the Moon, he discovered that the direction of the Sun's eccentric was changing, which in modern astronomy is equivalent to the Earth moving in an elliptical orbit around the Sun. His times for the new moon, lengths for the solar year and sidereal year, prediction of eclipses, and work on the phenomenon of parallax, carried astronomers "to the verge of relativity and the space age."

Copernicus mentioned his indebtedness to Al-Battani and quoted him, in the book that initiated the Copernican Revolution, the De Revolutionibus Orbium Coelestium.


One interesting point omitted from the above biographical detail is that Al-Battani came from a family who were members of the Sabian sect, a religious sect of star worshippers from Harran. Being worshipers of the stars meant that the Sabians had a strong motivation for the study of astronomy and astrology.

The limitations in Ptolemy's astronomical observations have led some later thinkers to describe his work as at best inaccurate and at worst fraudulent. For example, In 1753 Tobias Mayer who was working on improved tables for the moon's orbit, noted in a letter to Leonard Euler, fundamental discrepancies in Ptolemy's work. Ptolemy had claimed to have based his theory of the sun's motion on his own careful observations of the equinox on a date equivalent to 26 September 139AD. But later calculations showed that Ptolemy's time for the equinox was 30 hours late.

Mayer had found that the data had been taken from Hipparchus, and since Ptolemy had already built his whole system upon it he may have preferred to discard any of his observations that did not fit rather than start all over again. He may have thought no one would notice. Others also discovered that Ptolemy had fudged his data. Many of the results of his own observations and those copied from others were wrong. His models of the motions of the Moon and Mercury especially conflicted with the most elementary observation.

In his thesis, "The Crime of Claudius Ptolemy" (1977), Robert Newton states that the Almagest "has done more damage to astronomy than any other work ever written and astronomy would be better off if it had never existed".

I haven't read the book and I am not endorsing that extreme viewpoint personally but it is worth acknowleding that Ptolemy has had criticism for many of his supposed astronomical observations. This has led some like Robert Newton to suggest it was based on the work of Hipparchus and others rather than his own research. It is regretable that nearly all the written work of Hipparchus have been lost to history.
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Deb
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Posted: Mon Mar 01, 2010 9:02 am    Post subject: Reply with quote

Hi Mark

The last time I read through the Almagest I noticed how frequently Ptolemy mentioned his sources and pointed out that he chose this theory or that, from so or so, over this theory or that, because of .... whatever.

It drove home to me the point I had noticed in his other works, that Ptolemy did not claim originality for the ideas presented. He just explained the best of the theories available at the time, and stated which ones he preferred. The book is brilliant for what it is; flaws and all. It was bound by Aristotelian opinion but still managed to take astronomical logic forward and break some of the old ideas. As an astronomical manual there was nothing else to compare with it - until the later Arabic works, which built upon it.

This is what we see Ptolemy doing in the Tetrabiblos also. Again, he does not claim originality through original research, he simply wrote a treatise concerning the subject as a statement on the methods of his day.
But authors need reasons for books, and scholars need reasons for articles, and so the fashion seems to have become to popularise a myth before exposing it as an untruth.

Its a modern mindset for an individual to claim glory by inventing a host of new ideas - anciently, respectability and reputation came from showing knowledge of pre-established principles and the works of older sources. A well informed expert might venture an opinion or two but their expertise was first established by demonstrating their knowledge of older works. Ptolemy certainly acknowledged the influence of Hipparchus.

We also have to realise that there was a lot of mathematically idealised units being used in ancient astronomy, and these ideas were not quickly perfected because they represented philosophical principles too. Ptolemy's only crime, was to be representative of his era; but for every shortcoming of that era came a host of scientific developments and improvements which simultaneously arose from the same 'flawed' logic.

So the quote from Robert Newton is just ridiculous - there was no viable or informed alternative to Ptolemy's Almagest and modern science could not have developed without it. It's the equivalent of saying "all this early nonsense of looking at how the planets appear to move when viewed from the Earth has done nothing but damage because we all know the planets move around the Sun and should have intuitively divined that knowledge from the start, without all the evidence that we gained from our explorations via the geocentric perspective".

But how convenient to lump everyone who perpetuated geocentricty under the villainy of a liar like Ptolemy. This sort of attitude usually takes a sidesweep at the fact that astronomers screwed the whole thing up by thinking like astrologers too.
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margherita



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Posted: Mon Mar 01, 2010 11:46 am    Post subject: Reply with quote

Happy to hear this

Deb wrote:


So the quote from Robert Newton is just ridiculous - there was no viable or informed alternative to Ptolemy's Almagest and modern science could not have developed without it. It's the equivalent of saying "all this early nonsense of looking at how the planets appear to move when viewed from the Earth has done nothing but damage because we all know the planets move around the Sun and should have intuitively divined that knowledge from the start, without all the evidence that we gained from our explorations via the geocentric perspective".

But how convenient to lump everyone who perpetuated geocentricty under the villainy of a liar like Ptolemy. This sort of attitude usually takes a sidesweep at the fact that astronomers screwed the whole thing up by thinking like astrologers too.



This morning I wanted to write something, but then I kept my Mars quiet Smile
Ptolemy lived 1300 years before Copernicus and 1500 before Galilei, some mistake could be allowed, I think.

Sometimes I read these bad reviews about Ptolemy- the same Ptolemy in other conversations I tend to dismiss, i like to be the nasty girl Smile - and for me are unexplicable.

Astrologers practiced Ptolemy astrology- even Lilly book about nativities is in practice a comment to Tetrabiblos.

I even wonder how a traditional astrologer can read a chart without using Ptolemy method, considering that Giuntini, Nabod, Cardano, Campanella, all wrote their comment to Tetrabiblos- Bezza uses their comment for his astrology courses.

When Aristotelism died, astrology died because Ptolemy had linked so much these two disciplines that the one cannot live without the other.

For me, I dream someone who translates in English (or in Italian) at least one of the comments to Tetrabiblos--- whatever author i would love

margherita
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Posted: Mon Mar 01, 2010 12:13 pm    Post subject: Reply with quote

It doesn't seem popular around here to suggest that astrology may indeed have taken a wrong turn with Ptolemy. But then there are those who grant Ptolemy back door supremacy by telling us how wrong, misguided and conniving he was. Both sides equally need Ptolemy. This is (part of) the current state of astrology. Laugh, or weep your choice or inclination.
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Mark
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Posted: Mon Mar 01, 2010 12:55 pm    Post subject: Reply with quote

Hi Deb,

Quote:
The last time I read through the Almagest I noticed how frequently Ptolemy mentioned his sources and pointed out that he chose this theory or that, from so or so, over this theory or that, because of .... whatever.


Thats true. He frequently cites the works of Hipparchus for example. I have never subscribed to the view that he was in any way trying to swindle others into believing it was all his own work. Not least because these works would have been available to study in his time.

Quote:
Ptolemy did not claim originality for the ideas presented. He just explained the best of the theories available at the time, and stated which ones he preferred. The book is brilliant for what it is; flaws and all. It was bound by Aristotelian opinion but still managed to take astronomical logic forward and break some of the old ideas. As an astronomical manual there was nothing else to compare with it - until the later Arabic works, which built upon it.


It is undeniable the book is a masterpiece of its time. Certainly nothing we possess prior to this such as the work Geminus comes remotely close to the scope or depth of the Almagest. Little wonder the Greeks and Romans referred to him as 'The Divine Ptolemy'

Quote:
This is what we see Ptolemy doing in the Tetrabiblos also. Again, he does not claim originality through original research, he simply wrote a treatise concerning the subject as a statement on the methods of his day.
But authors need reasons for books, and scholars need reasons for articles, and so the fashion seems to have become to popularise a myth before exposing it as an untruth.


Yes its very much part of our culture to trash heroes. We always have to knock them down off their pedestals. In the past though often the reverse was the case. Thus a towering scientific figure like Ptolemy could become a barrier to further progress and enquiry. This was not his fault but his successors lack of rigour in challenging his assumptions. That is why I mentioned Islamic sources so much. On the whole they challenged many of Ptolemy's calculations much sooner than in Europe. In Europe the Church became wedded to the Aristotlean, Ptolemaic world view against any new sciencific paradigm. However, where new astronomical findings were compatible with the overall Ptolemaic worldview (such as the Alfonsine tables) they were clearly acceptable.

Quote:
Its a modern mindset for an individual to claim glory by inventing a host of new ideas - anciently, respectability and reputation came from showing knowledge of pre-established principles and the works of older sources. A well informed expert might venture an opinion or two but their expertise was first established by demonstrating their knowledge of older works. Ptolemy certainly acknowledged the influence of Hipparchus.


Some academics would go a lot further than that. In particular it has been claimed that Ptolemy's star catalogue was basically that of Hipparchus with star positions adjusted fot precession.

Quote:
We also have to realise that there was a lot of mathematically idealised units being used in ancient astronomy, and these ideas were not quickly perfected because they represented philosophical principles too. Ptolemy's only crime, was to be representative of his era; but for every shortcoming of that era came a host of scientific developments and improvements which simultaneously arose from the same 'flawed' logic.


This is again why the Islamic astronomers are important. They took mathematics well beyond what was possible in Ptolemy's time. There calculations were therefore a significant improvement on the best of Greaco-Roman astronomy. Like Ptolemy though they were coming from their own cultural paradigm. Much of the Islamic drive for accurate calculations came from the need to plot the position of Mecca and time the 5 daily payers would take place across the Islamic World.

Quote:
So the quote from Robert Newton is just ridiculous - there was no viable or informed alternative to Ptolemy's Almagest and modern science could not have developed without it. It's the equivalent of saying "all this early nonsense of looking at how the planets appear to move when viewed from the Earth has done nothing but damage because we all know the planets move around the Sun and should have intuitively divined that knowledge from the start, without all the evidence that we gained from our explorations via the geocentric perspective".


Although I haven't read Robert Newton I agree his basic proposition is preposterous and academic grandstanding.

Bear in mind though that my post was simply picking up the point of Johannes about what appear to be errors in Ptolemy's Star Catalogue. I haven't researched this topic much but I suspect the major reason was scribal error in the edition passed down to us. Nevertheless, for all its wonders noone can avoid the plain fact that there were astronomical problems integral to the Almagest. These inevitably had some impact on the accuracy of the astrology of those who followed Ptolemy to the letter. Not least the calculation of the rate of precession. By the time of the Islamic astronomers in the 9th century these problems necessitated a root and branch review of Ptolemy's calculations in the Almagest.
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Mark
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Posted: Mon Mar 01, 2010 1:03 pm    Post subject: Reply with quote

Margherita wrote:

Quote:
Astrologers practiced Ptolemy astrology- even Lilly book about nativities is in practice a comment to Tetrabiblos.

I even wonder how a traditional astrologer can read a chart without using Ptolemy method, considering that Giuntini, Nabod, Cardano, Campanella, all wrote their comment to Tetrabiblos- Bezza uses their comment for his astrology courses.


I rather thought my post might get reaction from you! What you say is all true. Nobody can seriously deny the immense impact Ptolemy had on astronomy or astrology.
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Deb
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Posted: Mon Mar 01, 2010 1:31 pm    Post subject: Reply with quote

Quote:
Quote:
Quote:
Its a modern mindset for an individual to claim glory by inventing a host of new ideas - anciently, respectability and reputation came from showing knowledge of pre-established principles and the works of older sources. A well informed expert might venture an opinion or two but their expertise was first established by demonstrating their knowledge of older works. Ptolemy certainly acknowledged the influence of Hipparchus.



Some academics would go a lot further than that. In particular it has been claimed that Ptolemy's star catalogue was basically that of Hipparchus with star positions adjusted fot precession.


I'm not sure that ptolemy would disagree. In particular, his 7th book of the Almagest, where he talks about the stars, is completely full of acknowledgements to Hipparchus, with other acknowledgments to other astronomers, ... but time and again he goes back to Hipparchus because he considers him to have been the most reliable. He states right at the start that Hipparchus was his main source, and that his investigations confirm the theory that Hipparchus had already conjectured.

They'll be accusing him of stealing his eclipse data from the Babylonians next.

The Almagest was very elegant and very much to be respected as a 2nd century attempt to explain geocentric astronomy. And it provided pretty good techniques for predicting planetary positions. The knowledge was essential for the development of science, but when it started to become a nuisance, was when it made more sense for science to switch to the heliocentric model. Had we followed Tycho Brahe's model, which I personally think would have been the best system of all; then the 'so-called' (he didn't invent it, he only described it) Ptolemaic model would never have been seen as a threat to the development of modern science.

But anyway, as astrologers, we still use the geocentric perspective. In response to Kirk's comment, I don't see how anyone can suggest that astrology took a wrong turn with Ptolemy, because he didn't make any 'turns'. He wrote about astrology as most scholars in his era did, as part of an integrated body of knowledge that involved sensual perception of things that moved. Its only because his astronomical text was essential for its explanation of astronomical principles that his astrological text became important too.

I don't want to sound as it I'm championing Ptolemy; but all I ever see from academics is an urge to come up with some new theory on why his work can't be trusted. But patently it was trusted, and respected, and improved by those who actually took the trouble to read it and understand it.

(Perhaps Margherita, we should form a society, of people who just can't be bothered to have another dig at Ptolemy - even though he was wrong sometimes and his works are not the font of all knowledge Smile )


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margherita



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Posted: Mon Mar 01, 2010 2:49 pm    Post subject: Reply with quote

Hello again,

Deb wrote:

They'll be accusing him of stealing his eclipse data from the Babylonians next.


This is explained by Antonio Panaino in the lecture Astroart sent me.
Ptolemy mentions Babylonian data because in his time they had the fame to be very accurate, and for respect to traditional wisdom.
As you say in better words than me, Ptolemy does not want to build a NEW astrology or astronomy.


Quote:
(Perhaps Margherita, we should form a society, of people who just can't be bothered to have another dig at Ptolemy - even though he was wrong sometimes and his works are not the font of all knowledge Smile )


these are the very words I always repeat here in Italy Smile

p.s. Mark has been forgiven Smile

margherita
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Deb
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Posted: Mon Mar 01, 2010 4:23 pm    Post subject: Reply with quote

Quote:
Quote:
Deb wrote:

They'll be accusing him of stealing his eclipse data from the Babylonians next.


This is explained by Antonio Panaino in the lecture Astroart sent me.
Ptolemy mentions Babylonian data because in his time they had the fame to be very accurate, and for respect to traditional wisdom.


It might not have been obvious that I was being ironic, sorry. The point is that he had almost 1000 years of collected astronomical records to study, eclipse details going back to 749 BCE; so he and his colleagues could analyze the data mathematically. He didn't make all the observations himself of course - and neither did Hipparchus!

(I like this thread because it allows me to express annoyance with the whole world, and no one in particular. I'm going to check it everytime I have a teabreak and keep adding little ranting comments.)

Deb
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Mark
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Posted: Mon Mar 01, 2010 4:38 pm    Post subject: Reply with quote

Hello Deb/Margherita

How about 'Ptolemaists Reunited'? Very Happy

Its hard to see how western astrology could have developed the influence it did without Ptolemy's contribution. I know there are some hard core hellenistic astrologers who wish to diminish the importance of Ptolemy. However, this is next to impossible considering his historical influence. Astrology was given a large amount of respectibility simply because the author of the Almagest and Handy Tables also wrote about astrology. It gave astrology an entrance into sophisticated intellectual debate it would never have had otherwise.

I dont think astronomy or astrology took a 'wrong turn' as Kirk suggests. Far from it. The Almagest was a significant achievement. All the Arabic astronomers I mentioned earlier closely studied Ptolemy's work. The fact they were able to significantly improve on his astronomical findings is a testament to their ingenuity. However, they all did so with the help of Ptolemy's prior work. Thus to paraphrase Newton they were standing on the shoulders of a giant too see further. Clearly, no science operates in a vacuum. Ptolemy heavily relied on Hipparchus while Hipparchus made extensive use of Mesopotamian astronomical recordings.

Still at the risk of being labelled a Ptolemy basher and being cast into astrological Tartarus I do think its interesting to study some of the astronomical deficiencies in the Almagest. It helps reveal some of the problems with his Star Catalogue. Here is an article by the American astronomer Owen Gingerich entitled 'The Trouble with Ptolemy'.

http://www.jstor.org/pss/3080419

As its a JSTOR article its only free for those with University access. Despite the article title it is a good deal more respectful to Ptolemy's astronomical contribution than the ridiculous hyperbole of Robert Newton.
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Deb
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Posted: Mon Mar 01, 2010 5:00 pm    Post subject: Reply with quote

Owen Gingerich knows what he is talking about, but it's a defence of Ptolemy (abstract below).

Mark, do not bring us informed accounts, which we are then obliged to spend time reading. Bring us more of the uninformed biased rubbish, so we can make quick rants without having to think about things.



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Mark
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Posted: Mon Mar 01, 2010 5:15 pm    Post subject: Reply with quote

Hello Deb,

There is already a whole website entitled Cafe Astrology. So I suppose there is room for a 'cup of tea' thread. Wink

Just to get your blood boiling Deb/Margherita and allow you both the opportunity for full rant mode I should tell you Robert Newton has been publishing more on Ptolemy.... Twisted Evil

The Origins of Ptolemy's Astronomical Parameters by Robert R. Newton.......$16

Newton's 228-page typeset monograph is an outgrowth and amplification of a previous study entitled The Crime of Claudius Ptolemy. It addresses the paradox that, while the parameters that Ptolemy claimed to have derived from his astronomical observations are apparently accurate and, in Newton's view "bear some resemblance to reality," his purported observations appear to be, for the most part, fabrications. Rather than attempting to uncover the sources of Ptolemy's values in specific historical observations prior to his time, Newton attempts to explain Ptolemy's rationale in dealing with his astronomical parameters and calculations on the basis of an analysis of the mental processes involved. [ISBN 0-912025-02-6]

--------------------------------------------------------------------------------

The Origins of Ptolemy's Astronomical Tables by Robert R. Newton...........$16

In this 264-page typeset companion volume to The Origins of Ptolemy's Astronomical Parameters, Dr. Newton analyzes the tables that Ptolemy states he calculated from these "fabricated" observations and concludes that they were in large part copied from now-lost tables of the ancient Greek astronomers rather than having been calculated from observations made in Ptolemy's time. Of special interest is the chronological sequencing of the original tables based on the level of mathematics involved in their calculation. [ISBN 0-912025-03-4]

Get your orders in now: http://terpconnect.umd.edu/~tlaloc/archastro/cfapubs.html
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margherita



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Posted: Mon Mar 01, 2010 5:17 pm    Post subject: Reply with quote

Deb wrote:

It might not have been obvious that I was being ironic, sorry.

Deb


But I understood this, mine was a more general thought...I never will be able to write things put so well like you.

p.s but definetely yes Ptolemy was perfidious with Venus and Mercury epycicle..

margherita
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Deb
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Posted: Mon Mar 01, 2010 5:37 pm    Post subject: Reply with quote

Quote:
There is already a whole website entitled Cafe Astrology.


I took a look. It's a nice site. However, I ran a search and the only links that related to Ptolemy required me to buy a personality profile report.
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Eddy



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Posted: Mon Mar 01, 2010 8:51 pm    Post subject: Reply with quote

Here are some online calculating tools to convert from equatorial to ecliptical and vice versa. I remember that someone mentioned them a year ago and found the website by chance last week.
http://www.antonblog.net/tools/
http://www.antonblog.net/tool/coordinates.html

MarkC wrote:

How about 'Ptolemaists Reunited'? Very Happy

If I had to choose between Ptolemaists Reunited and FC Hellenistics then I'd go for the Ptooligans.

Deb wrote:
(I like this thread because it allows me to express annoyance with the whole world, and no one in particular. I'm going to check it everytime I have a teabreak and keep adding little ranting comments.)

Deb
I always go here http://www.verbon.biz/ Smile.
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