Comet of 841–842

X/841 Y1 (Nithard)
Nithard's account of the comet – stella cometis, seventh line from the top, capital S
Discovery
Discovery date17 December 841
Orbital characteristics
Observation arc~2 months
Eccentricity~1.000
Last perihelion22 December 841
Physical characteristics
1.0
(841 apparition)

Comet X/841 Y1, also called the Comet of Nithard, was a comet that was visible in China and Europe between December 841 and February 842. The Japanese monk Ennin and the Frankish historian Nithard provide contemporary records of the comet from opposite ends of Eurasia. The comet is recorded in several other Chinese and European sources.

The comet appeared around the time of the winter solstice in the constellation Piscis Austrinus and it disappeared almost two months later in Camelopardalis. As its appearance coincided with a Frankish civil war, several European sources imbue it with ominous significance.