Aries 10° (System A) and Aries 8° (System B)

Definition

Aries 10° and Aries 8° are the two sidereally-fixed vernal-point norms of the Babylonian lunar systems: the equinox falls at solar longitude Aries 10° in System A and at Aries 8° in System B. Neugebauer documents both norms embedded in the length-of-daylight tables of each system and stresses that Babylonian longitudes are reckoned sidereally — with respect to the fixed stars — with no trace of any recognition of precession. The two-degree difference between the two norms is the central piece of evidence in the long debate over an alleged Babylonian discovery of precession.

In Tradition

Neugebauer, with Hunger-Pingree concurring, refutes the Schnabel thesis that the shift from Aries 10° to Aries 8° records a correction-for-precession made between Nabu-rimannu and Kidinnu. The decisive Neugebauer counter-argument is that the two norms are applied simultaneously throughout the whole Seleucid period and even later in Greek astrological texts, with no trace of any increasing deviation between the two systems such as a precession-recognition in one but not the other would produce.

In Practice

For the reader of an ACT lunar procedure text or ephemeris, the Aries 10° / Aries 8° norm fixes the coordinate frame: a System A column referencing the equinox places the vernal point at Aries 10°, a System B column at Aries 8°. Neugebauer's essay [16] reconstructs Schnabel's seven arguments A-G for a Babylonian precession-discovery and dismantles each: argument E (VAT 7821) collapses because cuneiform 7 and 4 are easily confused; argument D collapses because columns H and J are tied on arithmetical grounds and cannot represent independent phenomena; arguments B and C collapse because Sachs and Neugebauer established that almost all entries in the Seleucid observation texts are computed and not observed. The analogous Greek case is decisive: Eudoxus normed the vernal point at Aries 15° while Hipparchus normed it at Aries 0°, only two centuries apart — far too large to be caused by precession. The Aries 8° norm reappears in Hellenistic astrology and in Theon of Alexandria's "trepidation" theory.

Historical Origin

Attested in the System A and System B lunar procedure-text and ephemeris corpus from Babylon and Uruk (c. 250-50 BCE), within length-of-daylight tables and planetary procedure texts. Modern critical treatments: Otto Neugebauer, *Astronomy and History: Selected Essays* (Springer 1983), essay [16] sections 3, 5-10, 11, 13, vol. pp. 247-253; essay [17] section 3, vol. p. 259.

Further Reading

• Otto Neugebauer, Astronomy and History: Selected Essays
• Hermann Hunger & David Pingree, Astral Sciences in Mesopotamia