Message #47962

[Bianca]

A.2.1. Stars Along Circles Direct examination of the photographs of the Farnese Atlas can show what specifi c parts of various constellations are depicted as being exactly on the globe’s circles. For example, the westernmost edge of Aries’s horn is drawn as being on the equinoctial colure, and this is unambiguously identified with the star γ Ari. The chest of Leo is on the Tropic of Cancer, and this is identified with the star α Leo (Regulus). Lists of these stars can be used to determine the epoch of the Farnese Atlas’s constellations as being the year in which these stars-on-circles most closely match the circles. When calculated for this best epoch, the average positions of these stars-on-circles will provide an accurate measure of the positions of the circles.



I have compiled a list of specific stars that correspond to specific positions within constellations depicted as being exactly on one of the celestial circles. This list is presented in Table 3. The individual columns are

(1) a running number for counting and reference,

(2) the identification of the circle,

(3) the position description of the part of the constellation that is exactly on the circle,

(4) the modern name for the star that matches the position description,

(5) the right ascension (α) in degrees of the indicated star for the epoch 125 B.C.,

(6) the declination (δ) in degrees of the indicated star for the epoch 125 B.C., and

(7) the deviation in degrees between the target and the observed value. This deviation will depend on the circle; for example item number 1 is the colure for which α = 0° is the target while the observed value is α = 0.5° for a deviation in observed-minus-predicted equalling 0.5°.

Another example is item number 31, where the target is δ = –23.7°19 and the star had a declination of –27.3° for a deviation of (–27.3°) – (–23.7°) = –3.6°. The precession was calculated with the exact formula given by J. Meeus.

20 The choice of the date (125 B.C.) is justified in Sections 3.1 and A.2.4 as being the best fit date.