Dodecatemoria are subdivisions of the twelve signs of the Zodiac into a further twelve parts each. These can be said to form a "micro-zodiac" of 144 dodecatemoria, each corresponding to 2.5° of the ecliptic. In an alternate usage, the dodecamorion refers to a point on the ecliptic reached by the addition of twelve times a given number of degrees within a sign, either to the original degree, or to the beginning of the sign.
The name "dodecatemoria" is a Latinization of the Greek δωδεχατημόρια (singular Gr. δωδεχατημόριον, L. "dodecatemorium" or dodecatemorion). The same concept is expressed by Hebrew: השנים עשר in Hebrew and by اثنا عشرية in Arabic.
Let T be a point at degree D of sign S. Add 12×D degrees to the beginning of sign S.
For example, to find the dodecatemorion of Capricorn 17, multiply 17 by 12 to get 204, and move 204° past the beginning of Capricorn. One arrives at Cancer 24. Cancer is the seventh dodecatemorion of Capricorn, corresponding to Capricon 15–17.5°. At the same time, Cancer 24 can be given as the exact "dodecatemorion" of Capricorn 17.
In an alternative and seemingly older Mesopotamian system, the dodecatemorion of a point in the heavens is computed by adding the degree multiplied twelvefold not to 0° of its sign but to the exact degree in question.
In symbolic terms: Let T be a point at degree D of sign S. Add 12×D degrees to D. Or, equivalently, add 13×D to S.
The earliest possible date for the use of the Babylonian microzodiac is naturally constrained by the earliest possible date for the zodiac itself, generally given as circa the fifth century BC.
The Babylonian system was apparently adopted by the Greeks, who frequently attributed astrological knowledge to Chaldeans or Egyptians. The Latin authors Manilius and Firmicus both describe calculations of dodecatemoria. Ptolemy in the Tetrabiblos, however, dismissed the computation of dodecatemoria as illogical.
Abraham Ibn Ezra, a Hebrew scholar writing in the twelfth century AD, described two systems. In one system, attributed to Egyptian scientists and gentiles, a sign of 30° is subdivided into 12 sections of 2.5°, corresponding to a sequence of the seven heavenly bodies, with repetitions. In the other, attributed to Enoch and the Ancients, each degree within a sign corresponds with one of the twelve signs, starting with the sign itself. In the latter system, the cycle repeats two and a half times within each sign; for example, the dodecatemoria of Libra would begin with Libra in the first degree and return to Libra at 13° and 25°.
Computation of dodecatemoria could have helped the ancient astronomer by, simply, giving him more symbolic data to interpret.
The dodecatemoria could also crudely represent the motion of the moon across the ecliptic during the course of one month. Possibly they use a "virtual moon", imagined conjunct with the Sun (i.e., new) at the beginning of a sign, to symbolize divisions within the sign.
A Greek text (found in two existing codicies) connects the dodecatemoria with the homo signorum ("Zodiac Man") in which zodiacal signs are allocated evenly across the body from Aries at the head to Pisces at the feet. In this text, body parts are listed alongside degree numbers 2, 5, 7, 10, etc., corresponding to increments of 2.5° rounded down. The order of body parts modifies the usual list to accommodate the special characteristics of the sign; for example, most of the animal signs have "tail" as their final part, while Scorpio has "sting", and the list in Gemini and Pisces is doubled.
Like the 12-part zodiac, division of the signs into body parts (equated at some point with the signs) could have allowed ancient astronomers to describe parts of the sky (and record observations of celestial bodies located therein) with greater precision and convenience. Late Babylonian texts also give rising times for dodecatemoria during the course of a single day.
The data used for the Babylonian computation of dodecatemoria, inverted and re-sorted, result in a scheme known as Kalendertexte (or Calendar Text), also used by Mesopotamian astrologers in the first millennium BC.
When sorted by day—as the data apparently are on tablets from Babylon, Borsippa, and Uruk c. 5th–4th centuries BC—the result describes a progression of 277° per day.
- Auguste Bouché-Leclercq, L'Astrologie Greque; Paris: Ernest Leroux, 1899; pp. 299–304.
- Shlomo Sela, Abraham Ibn Ezra's Introductions to Astrology: a parallel Hebrew-English critical edition of the Book of the beginning of wisdom and the Book of the judgments of the zodiacal signs; Leiden & Boston: Brill, 2017; pp. 63–65, 319–320.
- F. Rochberg-Halton, "Elements of the Babylonian Contribution to Hellenistic Astrology"; Journal of the American Oriental Society 108(1), January–March 1998; JSTOR.
- Theo G. Pinches, "Babylonian Legal Documents Referring to House Property, and the Law of Inheritance"; read 6 February 1883; Transactions of the Society of Biblical Archaeology, Vol. 8; p. 287.
- John Z. Wee, "Virtual Moons over Babylonia: The Calendar Text System, Its Micro-Zodiac of 13, and the Making of Medical Zodiology", In John M. Steele (ed.), The Circulation of Astronomical Knowledge in the Ancient World; Leiden & Boston: Brill, 2016;ISBN 9789004315631.
- Lester J. Ness, Astrology and Judaism in Late Antiquity; PhD dissertation accepted at Miami University (Oxford, Ohio), 1990; pp. 65–66, 98.
- O. Neugebauer & A. Sachs, "The 'Dodekatemorioa' in Babylonian Astrology"; Archiv für Osrientforschung 16, 1952–1953; JSTOR.
- C. P. Goold, Introduction to Manilius: Astronomcia, Loeb Classical Library; Harvard University Press, 1977; pp. li–liv. See also Astronomica, Book 2, lines 693–2.478.
- A. Sachs, "Babylonian Horoscopes"; Journal of Cuneiform Studies 6(2), 1952; JSTOR. "Whatever the reason for the subdivision of a zodiacal sign into a micro-zodiac, beginning with the zodiacal sign in question, may be, the mere existence of such a scheme seems to be good evidence for the Babylonian origin of the mechanism of a well known doctrine of Greco-Roman astrology: that of the dodekatemoria. According to this doctrine, from the given longitude l1 of, let us say, the moon at some moment of interest, one computes an astrologically valid, different longitude l2. In this way, the astrologer has at his disposal two different longitudes of the moon on the basis of which he can now make twice as many predictions as before."
- Lis Brack-Bernsen & John M. Steele, "Babylonian Mathemagics: Two Mathematical Astronomical-Astrological Texts"; in Studies in the History of the Exact Sciences in Honour of David Pingree, ed. Charles Burnett, Jan P. Hogendijk, Kim Plofker, & Michio Yano; Leiden and Boston: Brill, 2004; ISBN 90 04 13202 3; pp. 95–
- John P. Britton, "Studies in Babylonian lunar theory: part III. The introduction of the uniform zodiac"; Archive for History of Exact Sciences 64(6), November 2010; JSTOR.
- Otto Neugebauer, "Melothesia and Dodecatemoria"; Analecta Biblica 3, 1959; reprinted in Neugebauer (1983), Astronomy and History: Selected Essays (Springer).