John of Worcester, an English monk, recorded the sighting, on December 8, 1128, of two unusually large sunspots. Five days later a brilliant aurora borealis (northern lights) was observed in southern Korea. Sunspot activity is typically followed by the appearance of an aurora borealis, after a span of time that averages five days. Thus, the Korean sighting helps to confirm John of Worcester' s sighting.
Only heavy sunspot activity could have resulted in an aurora borealis viewable at a latitude as low as that of Korea most strengthens the argument.