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My Friends the Naked-Eye Stars

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#26 Alexandrite

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Posted 22 February 2024 - 06:46 PM

On the topic of Ptolemy's star catalogue - or rather, the work of his predecessor, Hipparchus, whose lost works Ptolemy may have based his "Almagest" on:

 

https://skyandtelesc...comes-to-light/

 

This is really interesting! They may have found part of Hipparchus' original writings on astronomy.

 

Also, you can read Ptolemy's "Almagest" here, translated by G.J.Toomer:

https://classicallib...EST_ENGLISH.pdf


Edited by Alexandrite, 22 February 2024 - 06:47 PM.

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#27 Urban Uraniborg

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Posted 21 March 2024 - 10:54 PM

Similar to Mayan libraries being stolen by the church(Dresden Codex) a Christian scribe painted over Hipparchus Star Catalog one thousand years ago. 

The Portion put under Multi spectral imaging is only two paragraphs from one page. 

There are other pages of the Codex Climaci Rescriptus in collections not yet under the lens of Multispectral Imaging.....

 

 

Hopefully there will be more recoveries soon! 



#28 careysub

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Posted 28 March 2024 - 07:39 PM

Thanks Tony! I am going to save this, it has a lot of good talking points to use for public outreach efforts.



#29 careysub

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Posted 28 March 2024 - 07:44 PM

On the topic of Ptolemy's star catalogue - or rather, the work of his predecessor, Hipparchus, whose lost works Ptolemy may have based his "Almagest" on:

 

https://skyandtelesc...comes-to-light/

 

This is really interesting! They may have found part of Hipparchus' original writings on astronomy.

 

Also, you can read Ptolemy's "Almagest" here, translated by G.J.Toomer:

https://classicallib...EST_ENGLISH.pdf

The idea that Ptolemy copied Hipparchus' catalog was always weakly supported speculation, based on conjectures about precession corrections, and now that we have evidence (contained in fact in your first link) is that it is nor true. Ptolemy would have had a better catalog if he had, and Ptolemy used a different coordinate system - his catalog is the result of original observation.


Edited by careysub, 28 March 2024 - 07:44 PM.


#30 Tony Flanders

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Posted 29 March 2024 - 05:22 AM

The idea that Ptolemy copied Hipparchus' catalog was always weakly supported speculation, based on conjectures about precession corrections, and now that we have evidence (contained in fact in your first link) is that it is nor true. Ptolemy would have had a better catalog if he had, and Ptolemy used a different coordinate system - his catalog is the result of original observation.


I personally don't believe that Ptolemy copied Hipparchus's catalog, but he almost certainly had a copy of it in his library. Ptolemy was acutely aware of Hipparchus; the Almagest cites the work of dozens of astronomers, and there are probably more citations from Hipparchus than from the next three combined.

It's generally assumed that Ptolemy switched from Hipparchus's more natural equatorial coordinates to ecliptic coordinates due to Hipparchus's discovery of precession. Precessing equatorial coordinates requires a huge amount of computation, which is challenging to do by hand and was particulary challenging before the decimal notation system was introduced. In ecliptic coordinates, by contrast, the latitude remains constant and you only have to add a small amount per year to the longitude.


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#31 careysub

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Posted 29 March 2024 - 10:10 PM

Well sure, as a well to do educated Alexandrian he would have a library of all relevant works - but the specific claim is the Ptolemy copied Hipparchus catalog and the evidence says he didn't, he made his own observations.

 

Ptolemy can be regarded as the first modern scientist and the greatest ancient scientist. He invented the modern scientific approach building a mathematical model from a great mass of raw observations, and his model worked very, very well. In contrast Aristotle, certainly the greatest ancient observer of the natural world did it without taking exact measurements and did not build any models.



#32 Tony Flanders

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Posted 30 March 2024 - 04:38 AM

Ptolemy can be regarded as the first modern scientist and the greatest ancient scientist. He invented the modern scientific approach building a mathematical model from a great mass of raw observations ...


I (and many others, likely including Ptolemy himself) think that honor should go to Hipparchus.

Ptolemy did develop a superb model of planetary motion, one of the crowning achievements of science. The model remained unchallenged for 1,300 years because it predicted the positions of the planets perfectly within the error of measurement possible at that time. Too bad the model turned out to be based on false assumptions!

 

Hipparchus failed to develop a model of planetary motion, but he did develop superb models of the motions of the Sun and Moon based on a great mass of raw observations. Ptolemy was merely extending that methodology to the planets. Though the word "merely" is misleading, since the motions of the planets are vastly more complex than the motions of the Sun and Moon.

 

Truly, Ptolemy's greatest legacy was being the author of the second most influential textbook ever written -- the greatest, of course, being Euclid's Elements, which remained the standard geometry textbook for more than two millennia.


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#33 careysub

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Posted 30 March 2024 - 03:10 PM

I (and many others, likely including Ptolemy himself) think that honor should go to Hipparchus.

 


Ptolemy did develop a superb model of planetary motion, one of the crowning achievements of science. The model remained unchallenged for 1,300 years because it predicted the positions of the planets perfectly within the error of measurement possible at that time. Too bad the model turned out to be based on false assumptions!

 

Hipparchus failed to develop a model of planetary motion, but he did develop superb models of the motions of the Sun and Moon based on a great mass of raw observations. Ptolemy was merely extending that methodology to the planets. Though the word "merely" is misleading, since the motions of the planets are vastly more complex than the motions of the Sun and Moon.

 

Truly, Ptolemy's greatest legacy was being the author of the second most influential textbook ever written -- the greatest, of course, being Euclid's Elements, which remained the standard geometry textbook for more than two millennia.

 

I (and many others, likely including Ptolemy himself) think that honor should go to Hipparchus.

I can go along with this - Ptolemy, like any other good scientist, did base his work of predecessors and Hipparchus probably should be given credit for introducing the model-building approach.


Ptolemy did develop a superb model of planetary motion, one of the crowning achievements of science. The model remained unchallenged for 1,300 years because it predicted the positions of the planets perfectly within the error of measurement possible at that time.

So far, so good.

 

Too bad the model turned out to be based on false assumptions!

 This is getting on to thin ice.

 

Using his basic model approach (same as Hipparchus) he successfully developed a predictive model that fit the observations available. He did not have any data that disputed that the Earth could be at the center of the system. Choosing an Aristarchian heliocentric model was an option, but there was no actual reason for preferring it (Aristarchus thought  the Sun should be at the center because it is larger - though nothing known required this). There was no reason to suppose a different model should be used. The absence of stellar parallax was in fact a valid objection to a model with moving Earth. No one at that time did the experiment that Galileo did with occulting stars with ropes at great distance, which revealed their small diameters and provided a basis for estimating their distances (if one assumed they were luminous like the Sun) which would have destroyed the parallax argument.

 

It is helpful to realize that Copernicus did not propose a modern theory of planetary motion. Although it is somewhat heliocentric (the center of the system is not the Sun but a point offset from it) it was very similar to Ptolemy's in every other respect with perfect circular orbits and all the planets following epicycles. The Copernican theory did not take over quickly because it was not really superior, it was just as computationally complex did not have better accuracy. It would be incorrect to assert that it was based on correct assumptions in contrast to Ptolemy. It did have some explanatory advantages - seasons due to Earth's axial tilt, and although his explanation of retrograde motion was better he still needed the epicycles for his circular orbits to match the data.

A superior heliocentric model only emerged with Tycho Brahe's superior observations, and Kepler determining the Keplerian orbits from the data, which dispensed with the epicycles and placed the Sun at the true center. Better data, better analysis, leads to a better model, much closer to the truth, as well as being more accurate and easier to compute (which is all Kepler knew for sure at the time). Kepler's model simplified the heliocentric model and improved its accuracy and really provided the basis for the overthrow of Ptolemy.

One factor that did help cement the heliocentric model in place was an observation that did not really prove anything but changed the philosophical underpinnings of the worldview of scientists at the time: Galileo's discovery of the moons of Jupiter. It did not prove anything about the heliocentric system, but by showing that not everything orbits the Earth it demolished that assumption as a philosophical prior.


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#34 Tony Flanders

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Posted 30 March 2024 - 08:44 PM

Using (Ptolemy's) basic model approach (same as Hipparchus) he successfully developed a predictive model that fit the observations available. He did not have any data that disputed that the Earth could be at the center of the system.


I'm not sure we should continue this discussion in this thread, because we're getting quite far from the original subject. But I certainly agree with both of those statements.
 

Choosing an Aristarchian heliocentric model was an option, but there was no actual reason for preferring it.


Well, no, there was indeed a reason, but Ptolemy didn't see it. If he had started with the assumption that Earth orbits the Sun and then -- unlike Aristarchus -- actually sat down and done all the math, he would have realized that the heliocentric model is mathematically much simpler and more elegant, and allows much faster computations.

 

That is precisely what Copernicus did, and when his book was published everybody who was anybody instantly realized that Copernicus's model was much less cumbersome. So even astronomers who fervently believed that Copernicus's model was false used it for practical computations.

 

Tycho's model is computationally identical to Copernicus's but allows a stationary Earth. In that model the Sun orbits Earth and all the other planets orbit the Sun.

 

Ptolemy's model was unnecessarily complex because he introduced one epicycle per planet to account for retrograde motion. In Copernicus's and Tycho's model, one cycle -- Earth's orbit around the Sun or vice versa -- does the work that Ptolemy needed five to accomplish.
 

The other major false assumption in Ptolemy's model -- one that was deeply rooted in the Greek worldview -- was that all celestial motion is necessarily circular and at uniform speed. Kepler's laws, which show that planets move at non-uniform speeds on elliptical orbits, were truly revolutionary. Not a single astronomer before Kepler thought to challenge the assumption of uniform circular motion.


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#35 mountain monk

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Posted 31 March 2024 - 09:25 AM

Well, the discussion may have drifted, but it sure is interesting to me. Thanks.

 

Dark skies.

 

Jack


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#36 GeorgiaBrewer

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Posted 02 April 2024 - 05:46 PM

The magnitude system established by Ptolemy is still used in astronomy today. It really helps to estimate the brightness of stars, taking into account various factors. The concept of the brightness and visibility of stars in the sky remains surprising and intriguing, especially in the face of urban light pollution. Observing stars of different magnitudes under different conditions always brings its own flavor to astronomical observations and leaves a lot of room for admiration and reflection about our universe.




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