Comets and political anxieties in the first half of the ninth century: new light on comets X/839 B1 and X/841 Y1

A re-examination of early and late medieval annals and chronicles from Eastern and Western countries has enabled computation of approximate orbits for two medieval comets: X/839 B1 and X/841 Y1, which appeared soon after the return of 1P/Halley in 837. Furthermore, a historical and comparative study of 9th-century annals and chronicles from both eastern and western countries has highlighted interesting similarities in the way comets were treated in Continental Europe and early China. For both cultures the crossing of a bright comet in the sky was interpreted as a prefiguration of political turmoil, moral downfall and a reflection of bad kingship.