cubit (KÙŠ / ammatu)

KYOO-bit

babylonian: ammatu (Akkadian) / KÙŠ (Sumerogram); subdivides into digits ŠU.SI / ubānu

Definition

The cubit (Akkadian ammatu; Sumerogram KÙŠ) is the Babylonian angular measurement unit used in the Astronomical Diaries and Normal Star Almanacs to record positions of the Moon, planets, and conjunction-events against the kakkabū minâti (Normal Stars). One cubit equals 2;30° (2°30′) in the Hunger-Pingree convention, subdivided into digits (ŠU.SI / ubānu) at 1 digit = 0;5° (5 arcminutes). Direction-markers paired with cubit-and-digit values record observational position: "above"/"below" mark latitudinal offset, "in front of" (= west)/"behind" (= east) mark longitudinal offset.

In Tradition

Hunger and Pingree document the cubit as the Diaries-genre observational-position unit at 1 cubit = 2;30°. Neugebauer treats it as a 2° Babylonian angular norm attested in Hipparchus — a concrete trace of Babylonian-to-Greek transmission. The two values reflect different documentary contexts. Roughton and Canzoneri (1992) emphasise that actual Diaries measurements record longitudinal differences on the ecliptic without regard for latitude, even when "above/below" directional markers appear.

In Practice

For the reader of an Astronomical Diary or Normal-Star Almanac, the cubit is the unit by which lunar and planetary positions are anchored against a named normal star. Rochberg edits horoscope texts (Babylonian Horoscopes Texts 13-18) in which the moon's birth-position is fixed by a cubits-and-fingers offset — Text 14 records the moon "below the rear star of the head of the Hired Man" (α Arietis); Text 18 places it "west of the northern star of the Chariot" (β Tauri). The cubit's purely arithmetical character — distance in cubits and digits rather than degrees of ecliptic longitude — distinguishes Babylonian observational astronomy from its Greek descendant: the Greek tradition adopts the unit via Hipparchus but recasts the measurement against a geometric celestial-sphere model. Neugebauer essay [34] documents a second metrological-chain use where 1 cubit = 180 barleycorn ≈ 2½° (15° = 1080 barleycorn) in the Seleucid-period ephemeris context. Per Roughton-Canzoneri, the actual numerical measurements track longitude alone.

Historical Origin

Attested systematically in the Astronomical Diaries from Diary -652 onward, through the Late-Babylonian Normal Star Almanacs and Babylonian Horoscopes corpus (~410-50 BCE), with continued use in the Seleucid-period ACT ephemeris-metrology tradition. Transmitted to Greek astronomy via Hipparchus (2nd c. BCE). Modern treatments: Hermann Hunger & David Pingree, *Astral Sciences in Mesopotamia* (Brill 1999), p. 165 Ch. II §B.2.2; Otto Neugebauer, *Astronomy and History: Selected Essays* (Springer 1983), essays [31] and [34]; Abraham Sachs & Hermann Hunger, *Astronomical Diaries* (1988-1996); Roughton and Canzoneri (1992).

Definition

In Tradition

In Practice

Historical Origin

Further Reading