Author: VoijaRisa

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Scholarly History of Commentary on Ptolemy’s Star Catalog: Grasshoff (1990) – Refining the Catalog

Over the past several posts, I’ve used the excellent history of the scholarly discussion surrounding the star catalog in the Almagest as given in Gerd Grasshoff’s History of Ptolemy’s Star Catalogue. At this point, we’ve caught up to the time the book itself was published. However, we’re not even half way through the book. The remainder of the text is Grasshoff reviewing the previous authors and offering a more comprehensive and in-depth analysis than done previously.

But before getting into that, Grasshoff attempts to ensure that we really understand the Ptolemaic catalog in its own right. For Grasshoff, this requires “a meticulous edition of the text and a correct identification of the ancient positional description with the stars known by their modern names,” as well as “the accurate position of the star at the historical epoch.” Continue reading “Scholarly History of Commentary on Ptolemy’s Star Catalog: Grasshoff (1990) – Refining the Catalog”

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Scholarly History of Commentary on Ptolemy’s Star Catalog: Newton (1977)

In the past few posts, we’ve demonstrated a rapidly forming consensus that Ptolemy’s star catalog was largely an original work. However, there were some holdouts. In $1977$ R. R. Newton published the book The Crime of Claudius Ptolemy1. In this work, Newton generally agrees with Lalande and Delambre – That Ptolemy’s “observations” are not true observations, but merely the result of theoretical calculations, extending this argument well beyond the star catalog, which Newton frequently describes as “fabricated”.

As a forewarning, this book raised a great deal of popular media attention as the alleged scheming of scientists is always a popular topic, but scientists reviewing the book have generally panned it as using flawed methodology, as we’ll see. Continue reading “Scholarly History of Commentary on Ptolemy’s Star Catalog: Newton (1977)”

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Scholarly History of Commentary on Ptolemy’s Star Catalog: Gundel, Pannekoek, and Peter & Schmidt (1936-1968)

In the last post, we explored the 1925 paper by Vogt that attempted to reverse engineer entries from the presumed Hipparchan star catalog. Assuming that the coordinates derived were actually representative of such, Vogt demonstrated that Ptolemy was unlikely to have based his catalog on that of Hipparchus.

Continuing in the theme of defending Ptolemy, we’ll explore three more texts which come to Ptolemy’s defense: a book by Gundel (1936), a paper by Pannekoek (1955) and a paper by Petersen & Schmidt (1968). Continue reading “Scholarly History of Commentary on Ptolemy’s Star Catalog: Gundel, Pannekoek, and Peter & Schmidt (1936-1968)”

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Scholarly History of Commentary on Ptolemy’s Star Catalog: Vogt – 1925

In our last post we had established that it was impossible for Ptolemy to have stolen all of his data from Hipparchus as indirect evidence of the number of stars that would have been included in Hipparchus’ catalog indicate that Ptolemy’s catalog had around $200$ stars that Hipparchus’ presumptive catalog did not. Furthermore, we cited Dreyer and Fotheringham who both showed that errors in the determination of the position of equinoxes and solstices would have resulted in the $1º$ error at the heart of the accusation against Ptolemy, eliminating the need for Ptolemy to have used Hipparchus’ catalog.

Thus, while it’s not necessary that Ptolemy took all of his data from Hipparchus, the possibility remains that he took some. But to determine that, we’d need more information about Hipparchus’ presumed catalog which is what we’ll explore in this post looking at an important 1925 paper by Vogt. Continue reading “Scholarly History of Commentary on Ptolemy’s Star Catalog: Vogt – 1925”

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Scholarly History of Commentary on Ptolemy’s Star Catalog: 137 CE – 1918 CE

I’m going to take a bit of a break from direct progress on the Almagest as we get to the star catalog. This is because there is, what I feel to be a fascinating and important discussion surrounding its legitimacy and I want to explore the history of this discussion, even though almost all of it is outside the range of the SCA period2. Namely, the discussion is whether or not Ptolemy’s star catalog is legitimate, one which he took the measurements himself, or if Ptolemy stole the data from an astronomer that came before him and tried to update it, but failed due to an incorrect value for the rate of precession.

Continue reading “Scholarly History of Commentary on Ptolemy’s Star Catalog: 137 CE – 1918 CE”

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Scholarly History of Ptolemy’s Star Catalog Index

The discussion surrounding Ptolemy’s star catalog is a fascinating one. While astronomers for hundreds of years took Ptolemy’s catalog as authoritative, Tycho Brahe noticed that the positions of the stars had a $\approx 1º$ error in longitude. To explain this, Brahe hypothesized that this was due to Ptolemy stealing the data for the star catalog from Hipparchus and updating the longitudes with an incorrect constant of precession.

Astronomers have been debating this ever since.

Continue reading “Scholarly History of Ptolemy’s Star Catalog Index”

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Data: Stellar Quadrant Observations – 9/26/2022 (Jupiter Opposition)

Weather here in St. Louis has been outstanding this week. Highs in the 70’s and lows in the 50’s. Perfect autumn weather. And with it, crystal clear skies that made for some very nice observing during Jupiter’s opposition last night. Since Jupiter is a nice bright target, I headed out to Broemmelsiek Park to observe3.

Continue reading “Data: Stellar Quadrant Observations – 9/26/2022 (Jupiter Opposition)”

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Observing Results Time Lapse

Back in May of this year, I’d had a really good night observing. One of the things I always like is getting new stars added to the catalog. I still have the map I entered into Kingdom A&S in 2019 floating around my house and it’s fun to look back and see how much has gotten added since then. That night of observation added quite a few stars to be pile and inspired me to go back and animate the progress after each observing run which I placed on YouTube and then evidently forgot to share. So here it is!

Continue reading “Observing Results Time Lapse”

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Almagest Book VII: On the Method Used to Record [the Positions of] the Fixed Stars

Having established that the sphere of fixed stars has a rearwards motion, Ptolemy turns now to

making our observations and records of each of the above fixed stars, and of the others too, to give their positions, as observed in our time, in terms of longitude and latitude, not with respect to the equator, but with respect to the ecliptic, [i.e.,] as determined by the great circle drawn through the poles of the ecliptic and each individual star. In this way, in accordance with the hypothesis of their motion established above, their positions in latitude with respect to the ecliptic must necessarily remain the same, while their positions in longitude must always traverse equal arcs towards the rear in equal times.

Continue reading “Almagest Book VII: On the Method Used to Record [the Positions of] the Fixed Stars”

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Almagest Book VII: On the Rate of Precession from Other Greek Astronomer’s Observations

In the last post, we showed how we can determine the rate of precession if we know how much a star has changed its declination over a long period. In it, we used a baseline of $265$ years, corresponding to the time between Hipparchus and Ptolemy.

Next, Ptolemy wants to increase that baseline further and turns to the observations of three other Greek Astronomers: Timocharis, Agrippa4, and Menelaus. However, these astronomers did not give the position of the stars in equatorial coordinates. Rather, they described occultations of various stars by the moon. Thus, Ptolemy turns to the lunar model to determine the positions of these stars and instead of finding a change in declination, is able to directly compare the ecliptic longitude of them over time. Continue reading “Almagest Book VII: On the Rate of Precession from Other Greek Astronomer’s Observations”