Precision of Time Observation in Greco-Roman Astrology and Astronomy
Alexander Jones
Abstract
This article reviews the evidence for the precision of observed (or allegedly observed) time determinations in the Greek astral sciences. In the practice of astrology, the determination of times ‒most commonly times of births‒ was the province of lay observers, and the precision was not normally more refined than to the seasonal hour. In astronomy, the extant observational records show a broad trend towards more refined precision, though the apparent culmination of this trend in Ptolemy is due not only to his employment of the armillary astrolabe as a precision time-telling instrument but also to his penchant for fabrication and tampering in his observation reports. Ptolemy’s claims to have attained to unprecedented time precision in the observations on which his tables were ostensibly based likely contributed to their early and widespread adoption by astrologers.