Five monks at Canterbury Abbey reported witnessing a strange event: the upper horn of the crescent moon appeared to split, spewing fire, sparks, and smoke, before the moon flickered rapidly. Modern astronomers have speculated this account, dated to around this time, may describe a lunar impact event, possibly the formation of the crater Giordano Bruno, though the theory remains debated.
The account comes from the chronicle of Gervase of Canterbury, an English monk, who recorded that on a summer evening five men watched the moon's upper horn split in two, with a flaming torch springing up that scattered sparks, ashes, and glowing coals before the moon writhed like a wounded snake and returned to normal.
In 1976, astronomers Jack Hartung proposed this eyewitness account might describe the actual formation of the 22-kilometer crater Giordano Bruno on the moon's far side, caused by a large asteroid or comet impact. If true, it would be the only known human observation of a major lunar impact crater forming in real time.
Skeptics note the timing is inconsistent with the age of the crater as measured by other methods, and some argue the monks likely observed a meteor burning up in Earth's atmosphere directly in front of the moon, creating an illusion. The debate remains unresolved, making this one of astronomy's most tantalizing cold cases.