  The blinding of the Byzantine Emperor Constantine VI in Constantinople in
August 797 and his overthrow by his mother Eirene, who then until 802 ruled as
first female emperor of the Eastern Roman Empire, was used as legitimation for
the coronation of the Frankish King Charlemagne as emperor of the Romans on
December 25, 800, by contemporaries in Western Europe. Some observers in the
West may have even interpreted the downfall of the Eastern Roman emperor and
his replacement by a woman as sign of an impending collapse of the Roman Empire
and the entire world order as already expected, based on chiliastic
calculations. We equally find indications of apocalyptic expectations in
Constantinople, where the blinding of Constantine was linked with a spectacular
celestial manifestation of divine disapproval, a darkening of the sun for 17
days. In this paper, this obfuscation of the sun is compared with the
description of other atmospheric and climatic phenomena in the 8th and 9th
century as well as before and after this period. In addition, natural
scientific data is used to disprove earlier hypotheses on the physical
background to this event and to present a more probable scenario, i. e., the
impacts of one or more volcanic eruptions, for the darkening of 797 and other
phenomena, which provided a peculiar atmospheric framework for the
interpretation of the events between the downfall of Constantine VI and the
coronation of Charlemagne by contemporaries.
