Norming of the Zodiac
from pages 131 to 132 of The Heavenly Writing: Divination, Horoscopy, And Astronomy In Mesopotamian Culture by Francesca Rochberg
Since Ptolemy's Almagest, the beginning of the zodiac at 0 degrees Aries was fixed in relation to the vernal equinox, which however, moves westward at a constant rate of (1/72 degrees per year). The Babylonian zodiac was not counted from the vernal point, but was generally normed by the end points of zodiacal constellations, each one counted from 0 degrees to 30 degrees. This implies an ecliptic of 360 degrees, but Babylonian astronomy employed degrees within signs rather than a strictly numerical count of longitudes from 0 to 360. Also the longitudes assigned to the fixed stars were done so arbitrarily with the result that the zero point of the ecliptic did not coincide with the vernal equinox. That the Babylonian zodiac was sidereally fixed implies that regardless of date the fixed stars do not change their positions (degree of longitude) with respect to the norming point of the ecliptic.
The zodiac and the year itself were defined sidereally, so that one year was the time in which the returned to the same position with respect to a fixed star. The year that was counted from vernal equinox to vernal equinox, known as the tropical year, was not distinguished by the Babylonians from the sidereal year. To have done so would have been to recognize the fact that the equinoxes move - the precession of the equinoxes - and this has been ruled out for Babylonian astronomy.
In mathematical astronomical texts, the equinoxes and solstices were also normed sidereally at 10 degrees Aries in system A and 8 degrees Aries in System B. That the cardinal points of the year do not correspond to the zero points of the appropriate signs in the Babylonian zodiac is a result of the sidereal (rather than the tropical) construction of the zodiac. The two systems of Babylonian mathematical astronomy maintained the two norming points throughout the period of their use. As Neugerbauer pointed out, neither the chronological relation between Systems A and B Norms nor the reason for their difference is understood. That both vernal-point longitudes remained sidereally fixed, however, proves precession was not recognized.
The counting of the zodiac signs from Aries is a consequence of the origins of the zodiacal signs in the association between zodiacal constellations and the twelve schematic months of the year. Although the original list of stars in the "path of the moon" began at the end of Aries, specifically, with the Pleiades (choosing an exemplary star with longitude), the zodiac, when it is numerated in texts, begin with Aries. More precisely, however, we still cannot establish the star that originally served as norming point for the ecliptic. Even were we assume the vernal point was determined correctly when it was assigned 10 degrees then 8 degrees Aries, the corresponding dates for these zodiacal norming points cannot be pinpointed, as we do not sufficiently understand the ancient methods used to obtain those values. Comparison against modern values for the longitudes of equinoxes is therefore uninformative for this purpose.
Chapter 2. Introduction to Text Editions
1 Presentation of Horoscopes and Birth Notes
from page 17 of Babylonian Horoscopes by Francesca Rochberg
Dates have been established for the texts, or when a date is preserved, the dates are checked by means of planetary longitudes. These planetary longitudes are tabulated separately in the astronomical commentary to each horoscope, where the ancient data are compared against modern computed longitudes (see below chapter 2 2.1 Longitudes). The longitude tables present three columns: the list of seven planets, their longitudes (or position with respect to a normal star) found in the horoscope, and their longitudes computed by modern means. Rarely are degrees of longitude given in the texts. Ecliptical longitude is generally expressed with respect to the name of a zodiacal sign. And when degrees of longitude are given, these too, in the standard manner of Babylonian astronomical texts, are expressed with reference to the 30 degrees of a zodiacal sign, i.e., not with reference to a continuous 360 degree ecliptic. The Babylonian zodiac was at all times sidereal (see this chapter below 2.1) For comparison of ancient and modern data, my computation, wherever possible, also takes into account a time of birth. The hour (or approximate time) of birth is determined either from direct statements in the text, or approximated on the basis of other internal evidence (such as the position of the moon). In the total absence of evidence, planetary positions were computed simply for the time just after sunset, i.e., the beginning of the Babylonian day.
2 Methods of Dating
2.1 Longitudes
from page 19 of Babylonian Horoscopes by Francesca Rochberg
The horoscopes are not dated documents in the sense that the time of writing of the document is given. The date of birth, which is the key item, is given in all cases, but unfortunately is not always preserved. In most cases, establishing the date of the horoscope is a master of finding the closest fit between the ancient planetary longitudes given in the text and longitudes obtained through modern computation. To compare modern computed longitudes against those in a Babylonian source, it is helpful to correct for a systematic deviation in values that results from the different methods of counting longitude, i.e., modern tropical versus Babylonian sidereal longitudes. This systematic deviation represents the effect of precession upon the sidereally normed Babylonian zodiac.
Chapter 3 Elements of a Babylonian Horoscope
1.3 The Names Of Fixed Stars
from pages 30 and 31 of Babylonian Horoscopes by Francesca Rochberg
Omens based upon the appearances of fixed stars are known from Enuma Anu Enlil, but no mention is made of fixed star phases in the horoscopes. The references to stars in horoscopes are confined to the use of the ecliptical stars as a set of observational reference points. The Babylonian term for these stars was kakkabu minati (MUL.SID.MES) "counting stars," but have come to be known in modern terminology as normal stars after Epping's term Normalsterne. These stars lie close to the ecliptic, i.e. failling within a fairly narrow band of latitude between +10 degrees and - 7.30 degrees within which the moon and planets can be seen. The normal stars are most commonly found in the non-mathematical astronomical texts, especially the diaries, and normal star almanacs derived from the diaries. No complete list as such is attested in an ancient source, but about 34 normal stars are presently known. A useful list of the 32 most commonly occuring may be found in Sachs-Hunger, Diaries, pp. 17-19.
The normal stars provided a positional system which distance with respect to a certain normal star was noted in cubits (KUS = ammatu) and fingers (SU.SU = ubanu) where 24 fingers equal 1 cubit, and 12 fingers equal 1 degree. Directional terms "above" and "below" normal stars are more difficult to interpret. The normal stars as an ecliptical reference system are utilized in the horoscopes exclusively for citing the position of the moon. In these few horoscopes, the position of the moon seems to be given with reference to a normal star when it is above the horizon at (or near) the time of birth, and usually is given in addition to a zodiacal position. The normal star positions found in the horoscopes are almost certainly extracted from astronomical diaries.
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