Tracing the history of medieval astronomy
In the last post, we looked at how Menelaus’ theorem could be used to tell us which point on the ecliptic would culminate with a star. In this post, we’ll do something similar, but instead look at
the points on the equator and ecliptic which rise or set simultaneously with a fixed star. Continue reading “Almagest Book VIII: On Simultaneous Risings & Settings of the Fixed Stars”
Having laid out, in the last chapter, several “configurations” that Ptolemy finds of interest, he now goes about laying out a methodology by which they can be calculated “by purely geometrical methods.”
For the points on the ecliptic with which each fixed star simultaneously culminates, rises, or sets can be derived geometrically by means of the theorems [already] established.
In this post, we’ll explore specifically the culminations and leave the risings and settings for the next post.
Continue reading “Almagest Book VIII: On Simultaneous Culminations of the Fixed Stars”
In the next chapter, Ptolemy gives some configurations of stars that he considers important. These are in addition to stars being on straight lines with one another which we encountered previously. He outlines three general categories. Continue reading “Almagest Book VIII: Configurations of the Fixed Stars”
This past year, while working on researching the history of Ptolemy’s star catalog, I came across the following quote from Toomer:
Ideally one should provide a reconstruction of the outline of each constellation as it appears on Ptolemy’s star-globe. Unfortunately no one has done the necessary work of assembling and comparing all the literary and iconographic evidence from antiquity and from the derivative Arabic tradition (notably as-Sufi). This would be an interesting and valuable enterprise.
Essentially what Toomer is noting here is that, while historians of astronomy have spent considerable time trying to reconstruct what stars the catalog described, less attention has been paid to how the constellations looked.
Thus, I’m launching a spin-off from my main project to look at this topic. Continue reading “The Ptolemaic Zodiac Project”
The past month has been rather quiet here in the blog, but there was quite a bit going on for me behind the scenes due to Gulf Wars. This was largely due to the number of classes I taught. Continue reading “All Done with Gulf Wars XXXI”
It’s getting to that time of year where the weather becomes extremely unpredictable. Warm enough to have the windows open one day and an ice storm the next.
Despite it being cold this past Friday night, the sky was at least clear with no wind so Yseult and I went out to do some observing. Continue reading “Data: Stellar Quadrant Observations – 2/17/2023”
I’ll be teaching six classes at Gulf Wars this year. Information is below the fold! Continue reading “Gulf Wars 2023 Class Schedule”
Having laid out the general structure of the milky way, Ptolemy next describes the process of “the construction of the solid globe and the delineation of the constellations”. Continue reading “Almagest Book VIII: On the Construction of a Solid Globe”
Having laid out the star catalog, Ptolemy next faces a somewhat more abstract challenge: attempting to describe the nebulous structure of the Milky Way. He first describes the general shape and color:
Now the Milky Way is not strictly speaking a circle, but rather a belt of a sort of milky colour overall (whence it got its name); moreover this belt is neither uniform nor regular, but varies in width, colour, density and situation, and in one section is bifurcated. [All] that is very apparent even to the casual eye, but the details, which can only be determined by a more careful examination, we find to be as follows.
There’s not really much to discuss here, so instead, I’ll combine Ptolemy’s descriptions with some screenshots from Stellarium to help highlight what he’s talking about.
Continue reading “Almagest Book VIII: On the Location of the Milky Way”
In a previous post, we discussed a bit about Aratus’ poem, the Phaenomena, to which the Aratus Commentary was a response.
What I haven’t mentioned yet is that this original poem is still around. In fact, we have numerous copies of it thanks to it exploding in popularity in the $8^{th}$ century. However, sometime before then the poem itself had evidently been padded with other astronomical works. Among them were some descriptions of constellations. And these descriptions would provide new insight to our conversation. Continue reading “Scholarly History of Commentary on Ptolemy’s Star Catalog: The Aratus Latinus & Codex Climaci Rescriptus”