Five monks from Canterbury reported to the abbey's chronicler, Gervase, that shortly after sunset on June 18, 1178, they saw "two horns of light" on the shaded part of the Moon. In 1976 the geologist Jack B. Hartung proposed that this described the formation of the crater Giordano Bruno.
Giordano Bruno is one of the youngest large craters (22 km diameter) on the Moon. How old is "youngest"? Written accounts of twelfth century observations of a bright flash on the Moon may record the event that formed Giordano Bruno crater? That idea was proposed after the first high resolution pictures of the crater were analysed from the Apollo era of lunar exploration. Scientists could see that the crater was very young, and was in the area of the Moon corresponding to the bright flash, so it seemed possible that the flash and crater were related. More recently a team of scientists analysing high resolution images acquired by the Japanese lunar orbiter Kaguya estimated that the crater formed more than one million years ago. Very young by lunar standards, but certainly not consistent with the 12th century eyewitness reports! The Kaguya team determined the age of Giordano Bruno by counting the number of craters that formed on the crater subsequent to its formation. Read more
Ed ~ In 1178, Gervase of Canterbury reported seeing a bright flash on the Moon and some researchers believe that a crater called Bruno on the far side was the result, but doubt has been cast on this claim.