Message #47947

[Bianca]

Hipparchus was perhaps the greatest astronomer of Antiquity, his outstanding discovery being the precession of the equinoxes. He is said to have compiled a large star catalogue with at least hundreds of stars, although this catalogue has not survived. Indeed, only one of Hipparchus’s works has survived, the Commentary, which gives extensive quotes from both Eudoxus and Aratus.6 The thrust of the Commentary is to correct perceived errors in the Phaenomena by quoting the author’s own data and interpretation of the constellation figures. As a result, we can make a detailed comparison of Hipparchus’s personal descriptions with the Farnese Atlas. First the differences between Hipparchus and the globe:

(1) The head of Pollux is close to the Tropic of Cancer (and might even lie upon it), whereas Hipparchus says that the heads of both Twins are north of the Tropic and he even says that Pollux is north of the Tropic by 6°. But that is all: I can find only one non-universal difference between the globe and the Commentary. This difference is only quantitative, and it is only 1.7-σ in error (cf. Section A.2.1), which is not adequate grounds to claim a significant discrepancy. That is, the small shift of Gemini is typical of the scatter in the placement of the constellations, and so this is not grounds for considering the misplacement to be indicative. Another potential difference is that the globe depicts the modern Libra as a balance with the scorpion’s claws extending into it, while Hipparchus usually calls the constellation “The Claws”; however, in one place Hipparchus does recognize the constellation as “The Balance” (Commentary 3.1.5), so this cannot be regarded as being a true difference.



Now let us examine items in which the globe matches details particular to Hipparchus:

(A) Hipparchus explicitly corrects Aratus’s claim about the position of the Centaur (see item 2 above), and Hipparchus’s claim is matched by the depiction on the globe.

(B–G) Hipparchus also explicitly corrects Aratus’s items 7–12 above, and these corrections are entered onto the globe.

(H–J) Hipparchus explicitly corrects the Phaenomena by saying that the head of Draco is only close to the Arctic Circle, and that Crater and Corvus are south of the equator; all these items are as represented on the globe.

(K) Hipparchus states that the Arctic Circle is 37° from the north pole (i.e., at a declination of 53°), and this is reasonably consistent with my measured declination of 51.7° ± 0.9° for the Farnese Atlas.

(L) Item 3 (from the penultimate paragraph) is apparently corrected to agreement with the Atlas, as Hipparchus states that Eridanus has a second westward segment.

In all, the one difference is statistically insignificant while the dozen agreements between Hipparchus’s personal observations and the globe are close, many, and detailed. With this, we see that the comparison between the Atlas and Hipparchus is arguably perfect (other than the 9 itemized differences that are true for all ancient sources).