How often is Halley's Comet visible?
Halley's Comet
The Irish Annals of the Four Masters recorded the comet as "A star [that] appeared on the seventh of the Calends of May, on Tuesday after Little Easter, than whose light the brilliance or light of The Moon was not greater; and it was visible to all in this manner till the end of four nights afterwards."[71] Chaco Native Americans in New Mexico may have recorded the 1066 apparition in their petroglyphs.[73]