A revision of ∆T values for the V, VI and VIIth centuries

Studies of pretelescopic values of ∆T have been arranged by many authors. Ancient observational records of total and annular solar eclipses and in a lesser extend also lunar eclipses and occultation have been used to calculate limits to the value of ∆T [6], [7] and [8] among others. We provide a first approximation for computed values of ∆T from the Vth to the VII th centuries considering all the available ancient astronomical records, paying special attention to those from Western Europe for which new analysis and reductions have been carried out. We present two examples of ancient observations with their associated discussions that lead to new values of some astronomical parameters. Similar studies have been carried out for more than a hundred od ancient registers. The results obtained in the first instance corroborate those obtained by Soma and Tanikawa in the sense that the ∆T for these centuries seems to be significantly lower than that obtained by Morrison and Stephenson [2] and Stephenson et al. [7] 1. EXAMPLE 1: TOTAL SOLAR ECLIPSE. AD 418, July 19 This eclipse was collected in numerous no contemporary European chronicles from Austria, Denmark, Germany, France in many cases only reference is made to the darkening of the sun in broad daylight with or without mentioning the date. Other more complete records include the time of day the event took place. For these records, we must bear in mid a classical problem that usually appears when we deal with Medieval sources: non-contemporary authors were limited to copying records of other authors prior to them, for mainly prestige reasons. See [3], [6] for a further study. Anyway, some contemporary authors such as Hidatius, from Northern Spain and Philostorgius from somewhere near Istambul, provide valuable and more detailed data (http: //www.tertullian.org/fathers/philostorgius ̇fn.htm#218): When Theodosius had entered the years of boyhood, on the 19th of July, a little after noon-day, the sun was so completely eclipsed that the stars appeared; and so great a drought followed on this eclipse that a sudden mortality carried off great multitudes both of men and of beasts in all parts. Moreover, at the time that the sun was eclipsed, a bright meteor appeared in the sky, in shape like a cone, which some persons in their ignorance called a comet (. . . ) For it arose first in the east, just where the sun rises at the equinox, and then passing across the lowest star in the constellation of the Bear, crossed gradually over to the west (. . . ) it at length disappeared, after it had continued its course for more than four months. Its apex, moreover, at one time was carried up to a high and narrow point, so that the meteor exceeded the length and shape of a cone, while at another time it returned to that particular form. (. . . ) At the same time with the earthquakes, fire came down from the skies, which seemed to banish all hope of escape; however, it caused no destruction of life, for the mercy of God sent a violent wind which scattered the fire in every direction, and at length drove it into the sea. Then a new and strange sight was to be seen; the waves of the sea burning