Solar Activity Around AD 775 from Aurorae and Radiocarbon
Astron. Nachr. / AN 999, No.88, 789–812 (2011) / DOI please set DOI! Solar activity around AD 775 from aurorae and radiocarbon R. Neuhauser¨ 1 ⋆ and D.L. Neuhauser¨ 2 1 Astrophysikalisches Institut und Universit¨ats-Sternwarte, FSU Jena, Schillerg¨aßchen 2-3, 07745 Jena, Germany 2 Schillbachstraße 42, 07743 Jena, Germany Received Nov 2014, accepted 27 Feb 2015 Published online Key words AD 775 – solar activity – aurorae – sunspots – radiocarbon – history of astronomy A large variation in 14C around AD 775 has been considered to be caused by one or more solar super-flares within one year. We critically review all known aurora reports from Europe as well as the Near, Middle, and Far East from AD 731 to 825 and find 39 likely true aurorae plus four more potential aurorae and 24 other reports about halos, meteors, thunderstorms etc., which were previously misinterpreted as aurorae or misdated; we assign probabilities for all events according to five aurora criteria. We find very likely true aurorae in AD 743, 745, 762, 765, 772, 773, 793, 796, 807, and 817. There were two aurorae in the early 770s observed near Amida (now Diyarbakır in Turkey near the Turkish-Syrian border), which were not only red, but also green-yellow – being at a relatively low geomagnetic latidude, they indicate a relatively strong solar storm. However, it cannot be argued that those aurorae (geomagnetical latitude 43 to 50◦, considering five different reconstructions of the geomagnetic pole) could be connected to one or more solar super-flares causing the 14C increase around AD 775: There are several reports about low- to mid-latitude aurorae at 32 to 44◦ geomagnetical latitude in China and Iraq; some of them were likely observed (quasi-)simultaneously in two of three areas (Europe, Byzantium/Arabia, East Asia), one lasted several nights, and some indicate a particulary strong geomagnetic storm (red colour and dynamics), namely in AD 745, 762, 793, 807, and 817 – always without 14C peaks.
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