Rising Times

Definition

Rising times are an arithmetical scheme for how long each zodiac sign takes to climb across the horizon at a given latitude on Earth. The Babylonian version comes in two parallel forms — System A, a step-function with two values, and System B, a linear zigzag function — both tuned so that the longest day and the shortest day at the latitude of Babylon (32.5° N) keep the conventional 3:2 ratio. The length of daylight is found by adding up the rising times of the arc of the ecliptic that runs from the Sun's position to the point 180° away.

In Tradition

In the history of mathematical astronomy, Rochberg treats Babylonian rising times as one of the two clearest channels by which knowledge passed from Mesopotamia to Greece — the other being the zodiac itself. The originally Babylonian method for computing rising times can be traced in Vettius Valens (c. 150 CE), in Papyrus Michigan 149, and in Manilius. Hunger and Pingree agree, treating Systems A and B as the foundational tables from which the Greek tables of oblique ascension descend.

In Practice

For the Babylonian astronomer-scribe, rising times were the working tool that turns a position on the ecliptic into a time of rising and into a length of daylight; they were the apparatus against which the Goal-Year Texts and the ephemerides were checked. For the Hellenistic astrologer, Babylonian rising times are the technical groundwork for computing the ascendant — the degree rising on the eastern horizon — and for primary direction, a method that hands periods of life to one chart factor after another. Ptolemy's *Almagest* II.8 preserves a ten-latitude rising-time table that adapts the Babylonian System A scheme to other places, and the seven-climata tradition of medieval geography keeps traces of the Babylonian oblique ascensions far into the Middle Ages.

Historical Origin

Rising times are attested in Late-Babylonian mathematical astronomy of the Seleucid period (the ACT corpus, per Neugebauer 1955). The transmission is documented by Rochberg in *The Heavenly Writing* Ch. 7 §7.1, citing Neugebauer's *History of Ancient Mathematical Astronomy* (1975). They were taken into Greek astronomy by Vettius Valens (*Anthologiae*, c. 150 CE) and into Ptolemy's *Almagest* II.8 (the ten-latitude table) c. 150 CE, and preserved in the medieval seven-climata system.

Further Reading

  • Francesca Rochberg, The Heavenly Writing: Divination, Horoscopy, and Astronomy in Mesopotamian Culture
  • Hermann Hunger & David Pingree, Astral Sciences in Mesopotamia
  • Otto Neugebauer, A History of Ancient Mathematical Astronomy