Skyscript Astrology Forum

The situation with the accuracy of the modern re-calculations of the horoscope's longitudes in the Greek Horoscopes is actually worse. First edition of the Greek Horoscopes was in 1959, 5 years before the publishing of Planetary, Lunar, and Solar Positions A. D. 2 to
649 at Five-Day and Ten-Day Intervals by Briant Tuckerman, the standart reference source for all later scholars like prof. Pingree and others. Actually all computations in the Greek Horoscopes for the Moon and Sun and planets were carried out by means of Paul Viktor Neugebauer's tables published in the years 1914 and 1932 respectively. The accuracy is therefore not large and namely one degree.

The big difference in the values of Mercury in the ancient charts (the Sassanian and the Greek) between the text and the modern computations has a simple explanation. Mercury could not be observed during its conjunction with Sun and during most of the time it is invisible and consequently the positions show enormous errors where the predictions could not be observationally controlled. One example from the modern time: in Andrea Argoli, Ephemerides ab Anno MDCXXI ad MDCXL, Rome, 1621 the errors for Mercury's position for 1651 vary from + 5? to - 9?.