The Greek geographer Strabo of Amaseia, in Geography 16.1–.6, writes: "In Babylon a settlement is set apart for the local philosophers, the Chaldaeans, as they are called, who are concerned mostly with astronomy; but some of these, who are not approved of by the others, profess to be writers of horoscopes. There are also several tribes of the Chaldaean astronomers. For example, some are called Orcheni , others Borsippeni , and several others by different names, as though divided into different sects which hold to various dogmas about the same subjects. And the mathematicians make mention of some of these men; as, for example, Kidenas, Nabourianos and Soudines".
The Roman encyclopaedist Pliny the Elder, in Natural History II.vi.39, writes that the planetMercury can be viewed "sometimes before sunrise and sometimes after sunset, but according to Cidenas and Sosigenes never more than 22 degrees away from the sun".
The Roman astrologer Vettius Valens, in Anthology, says that he used Hipparchus for the Sun, Sudines and Kidynas and Apollonius for the Moon, and again Apollonius for both types.
The Hellenistic astronomerPtolemy, in Almagest IV 2, discusses the duration and ratios of several periods related to the Moon, as known to "ancient astronomers" and "the Chaldeans" and improved by Hipparchus. He mentions the equality of 251 months to 269 returns in anomaly. In a preserved classical manuscript of the excerpt known as Handy Tables, an anonymous reader in the third century wrote the comment that Kidenas discovered this relation.
A damaged cuneiform astronomical diary tablet from Babylon mentions that "ki-di-nu was killed by the sword" on day 15 of probably the 5th month of that year, which has been dated as 14 August 330 BC, less than a year after Alexander the Great conquered Babylon.
The following information is an excerpt of the overview of a century of scholarship in the sources referenced below. The meaning of tersitu is not known definitively. Already Franz Xaver Kugler proposed that the word can be interpreted here as "table"; in another context it seems to mean something like "tool", but in yet another it refers to a blue enamel paste. P. Schnabel, in a series of papers, interpreted the phrase as an assignment of authorship. He argued that Naburimannu developed the Babylonian System A of calculating Solar System ephemerides, and that later Kidinnu developed the Babylonian System B. A Greco-Roman tradition, mentioned above, attributes to Kidinnu the discovery that 251 synodic months equals 269 anomalistic months. This relationship is implicit in System B, and is therefore another reason to believe that Kidinnu was involved in developing the lunar theory of System B. However, the conclusion that Kidinnu is the main creator of System B is uncertain. Babylonian astronomers before Kidinnu's time apparently already knew the Saros cycle and the Metonic cycle ; both cycles are also used in System B. Schnabel computed specific years for the origin of the System B lunar theory, but Franz Xaver Kugler and Otto E. Neugebauer later disproved Schnabel's calculations. Schnabel also asserted that Kidinnu discovered precession when distinguishing between sidereal and tropical years; Neugebauer contested this and current scholarship considers this conclusion to be unfounded. The lunation length used in System B has also been attributed to Kidinnu. It is 29 days + 191 time degrees + 1/72 of a time degree = 29d 31:50:8:20 = 29d + 12h + 793/1080h = 29.53059414...d. Being a rounded value in the archaic unit of "barley corns" it may be even more ancient. In any case, it is very accurate, within about ⅓ of a second per month. Hipparchus confirmed this value for the lunation length. Ptolemy accepted and used it, as mentioned above. Hillel first used it in the Hebrew calendar, and it has been used for that purpose ever since. The existing evidence makes it difficult to put Kidinnu at a time and place. Schnabel placed Kidinnu in Sippar, but Otto E. Neugebauer showed that Schnabel based this conclusion on a misreading of the cuneiform tablet. Classical sources like Strabo mention different "schools" and "doctrines" followed in different places. System A and B have been used contemporaneously, and tablets for both systems have been found in both Babylon and Uruk. Tablets based on System B, associated with Kidinnu, have been found mostly in Uruk, but the earlier tablets came predominantly from Babylon. The oldest preserved tablet using System B comes from Babylon and dates from 258-257 BC. This is in the Seleucid era, but it is plausible that the traditional Chaldean astronomical systems had been developed before the Hellenistic period. The Alexander chronicle mentioned above suggests that the famous astronomer Kidinnu died in Babylon in 330 BC, if it refers to the same Kidinnu who was mentioned on the ephemeris tablets centuries later.
