Acronychal Risings in Babylonian Planetary Theory

Abstract

The Astronomical Diaries (ADT), and a few known collections for individual planets, contain observations of five synodic phenomena of superior planets: heliacal rising (F), first station (), acronychal rising (0), second station (^), and heliacal setting (£2). A date is given for each, in the case of F often both an observed date and a 'true' or 'ideal' date on which the rising is considered to have occurred even if it was not observed, as due to clouds, found by a measurement of the interval in degrees of time between the rising of the planet and the rising of the sun. However, location is recorded differently for each class of phenomena. Heliacal risings and settings, F and £2, are located by zodiacal sign, or by beginning or end of zodiacal sign. In some cases F contains a measured distance from a nearby 'normal' (standard) star or planet, for conjunctions of planets with stars or with each other were considered ominous. But it does not appear that measurements of distances from stars at F were used to establish location more precisely than by zodiacal sign, and distances from planets cannot be used to establish location. First and second stations, and ^, usually contain a measured distance from a normal star, presumably to determine when the planet was stationary, but sometimes only a location by zodiacal sign. Acronychal rising 0 contains no location at all. It could have been assumed that the planet was in the zodiacal sign opposite the sun, but no location for the sun is given in the Diaries. (It is curious that acronychal risings were observed at all since there are no omens associated with them. Yet an acronychal rising of Jupiter appears already in the second earliest known Diary, ADT -567, and one may wonder why.) Sometimes observations contain the remark 'not observed' (nu pap), which presumably indicates an inference of the date and location from nearby preceding or following observations. The dates and longitudes of the same phenomena reported in the Diaries are computed in the ephemerides to a degree of precision exceeding the observations in the Diaries. The ephemerides are published in ACT, and the further analysis in HAMA is essential. In a recent study of Babylonian planetary theory (Swerdlow, 1998), I set out a method by which the parameters of the ephemerides can be derived from synodic times between phenomena, recoverable from the dates in the Diaries, and locations no more precise than by zodiacal sign. The method depends upon a constant difference between synodic time and synodic arc, AT - AX = C, found in the ephemerides of all planets except Venus, which allows A X to be found from AT. With the exception of 0 and ^ of Mars, which occur in the retrograde arc, the ephemerides use the same functions for computing all phenomena of the superior planets by complete synodic arcs and synodic times even though the synodic arcs and times between consecutive heliacal risings or settings, which