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.
Initially, the descriptions were attributed to Aratus himself. However, beginning in the $19^{th}$ century, historians realized that the language better matched that of Hipparchus. Furthermore, the calculated epoch supported a Hipparchan origin. And perhaps most convincingly, the co-declination of Polaris precisely matched the one Hipparchus used according to Ptolemy, in another of his works, Geographia.
Yet while the Hipparchan origin of these descriptions has been known for quite some time, using them to compare to the Almagest was suspiciously absent from the conversation. Perhaps this is because there were only three constellation descriptions present in the extant manuscripts: Ursa Major, Ursa Minor, and Draco.
However, in 2012, biblical scholar Peter Williams, gave his students several pages from a text found at a Greek Orthodox monastery in Egypt. These pages contained Christian texts, but were known to have been scraped clean before the Christian text was added, removing a previous text (a phenomenon known as palimpsest). This text was known as the Codex Climaci Rescriptus.
The students imaged the pages under numerous colors of light and used computer algorithms to attempt to recover the latent text beginning in 2017.
They quickly realized that the texts were astronomical, containing star-origin mythos from Eratosthenes, but also segments of the Aratus Latinus and associated works. Among those associated works was the Hipparchan work, but this time included a new constellation: Corona Borealis.
The team compared the coordinates from the Aratus Commentary to the ones determined from the Codex Climaci Rescriptus for the stars that were common to each1 and determined they shared an excellent agreement, again affirming the Hipparchan origin.
The researchers compared the coordinates with those of Ptolemy and found they did not match. What’s more, they compared the distribution of errors and found that Hipparchus’ catalog was likely more accurate based on the limited selection of stars available.
Conclusions
In this series of posts, we’ve covered quite an expanse of history with opinions on all sides of the debate.
However, the consensus does seem to be building that it is impossible for Ptolemy to have been the author of most of his star catalog. At least some, and quite likely most, of the entries were based on work by Hipparchus.
Attempting to determine how much will likely be the question of historians in coming years.