large-hour (H; time-degree on equator)

LARJ-ow-er

babylonian: large-hour (modern scholarly notation H, following Neugebauer; cuneiform texts encode the unit by its sexagesimal value rather than by a single Akkadian or Sumerogram term)

Definition

The large-hour, abbreviated H in modern editions of the Babylonian mathematical-astronomy corpus, is a time-unit equal to 60 UŠ (time-degrees on the celestial equator), so that one day contains 6 large-hours (6;0 H = 6,0 UŠ = 360°) and each large-hour spans approximately 4 modern hours of solar time. The unit's function is computational compactness and disambiguation: it spans one-sixth of a day rather than one-twenty-fourth, and unambiguously marks time-degrees-on-the-equator as distinct from arc-degrees-on-the-ecliptic in System A and System B lunar ephemerides.

In Tradition

Hunger and Pingree, following Neugebauer, identify the large-hour as the canonical equatorial-time unit of System A and System B lunar mathematical astronomy. The unit's defining feature is the disambiguation it provides: degrees-on-the-ecliptic and time-degrees-on-the-equator both descend from the same UŠ but stand in different reference frames, and the H-notation marks the equatorial sense unambiguously. Neugebauer's 1957 reading of BM 36705+36725 established the column-Φ Saros-difference parameter 0;17,46,40 H, fixing the unit's role at the heart of the lunar-eclipse-prediction sequence.

In Practice

For the reader of an ACT-edition lunar ephemeris, the large-hour is the unit in which the most computationally central columns are tabulated. Hunger and Pingree note that "Both Φ and G are measured in large-hours (= H), which are actually time-degrees on the equator" (Astral Sciences p. 206), used to avoid confusion with ecliptic-degrees. Column C (length of daylight), column G (synodic-month-excess), and column K (total month-length) all carry values in H. Hunger and Pingree systematise the H/UŠ conversion (§C4.2a.1 p. 243): because 6 H = 6,0 UŠ, moving the sexagesimal place one position to the right converts any value in large-hours to the equivalent in UŠ. The convention is, in Neugebauer's formulation, the bridge that lets a single time-arithmetic framework connect synodic-month-length differences to eclipse-prediction without per-step unit-juggling.

Historical Origin

Attested throughout the Seleucid-period ACT corpus of System A and System B lunar ephemerides (~3rd-1st centuries BCE) — particularly columns Φ, G, C, K, and J of the lunar tables — and in their procedure-text companions. The unit's mathematical role established by Otto Neugebauer in *Astronomical Cuneiform Texts* (1955) and re-codified in Hermann Hunger & David Pingree, *Astral Sciences in Mesopotamia* (Brill 1999), pp. 206 + 243 (§C4.2a.1). Foundational text: BM 36705+36725 (Neugebauer 1957, establishing column-Φ Saros-difference 0;17,46,40 H).

Definition

In Tradition

In Practice

Historical Origin

Further Reading