Many writers dealing with the impact phenomenon have noted the apparent eyewitness impact on the Moon recorded by the monk Gervase of Canterbury in 1178. Because this event occurred close to the intersection of the Earth's orbit with the Taurid meteor stream, this event has sometimes been quoted as supporting the suggestion that large objects in the Taurid stream pose a special threat to the Earth. For example, Clube and Napier devote several pages to this hypothesis in their book "The Cosmic Winter". Specifically, the impact has been identified with he bright ray crater Giordano Bruno.
In his book "Rain of Iron and Ice", John Lewis provides the following translation of the report:
"In this year, on the Sunday before the feast of St John the Baptist, after sunset when the Moon had just become visible, a marvelous phenomenon was witnessed by some five or more men who were siting facing the Moon. Now there was a bright new Moon, and as usual in that phase its horns were tilted toward the east; and suddenly the upper horn split in two. From the midpoint in the division a flaming torch sprang up, spewing out, over considerable distance, fire, hot coals, and sparks. Meanwhile the body of the Moon which was below writhed, as it were, in anxiety, and to put it in the words of those who reported it to me, and saw it with their own eyes, the Moon throbbed like a wounded snake. Afterwards it assumed its proper state. This phenomenon was repeated a dozen times or more, the flame assuming various twisted shapes and then returning to normal. Then, after these transformations, the Moon from horn to horn, along its whole length, took on a blackish appearance. The present writer was given this report by men who saw it with their own eyes, and are prepared to stake their honor on an oath that they have made no additions or falsifications in the above narrative."
Following is a story just posted by Sky and Telescope that disputes the identification of this event with the crater Giordano Bruno, and thus undercuts the reality of the medieval report, or at least its relevance to NEO impacts and the Taurid meteor stream.
AN EYEWITNESS IMPACT DEBUNKED
Were a small asteroid to hit the Moon, could we see the impact with the naked eye? In his chronicles of medieval life, Gervase of Canterbury described a dramatic event witnessed on the evening of June 18, 1178:
"Now there was a bright new Moon . . . and suddenly the upper horn split in two. From the midpoint of this division a flaming torch sprang up, spewing out . . . fire, hot coals, and sparks . . . The body of the Moon which was below writhed . . . throbbed like a wounded snake. Afterwards it resumed its proper state. The phenomenon was repeated a dozen times or more. [Finally] the Moon . . . along its whole length took on a blackish appearance."
In 1976 geologist Jack B. Hartung (State University of New York) proposed that this passage describes the creation of Giordano Bruno, a relatively young, 22-kilometer-wide crater near the Moon's northeast limb. Hartung reasoned that, seen from Earth, this brightly rayed crater appears near the midpoint of the young crescent Moon. Astronomers were quick to counter that on the date in question the Moon was only 1.3 days past new and thus too near the Sun to be easily visible at all. Also, Gervase's witnesses claimed to have seen the "flaming torch" many times, which sounds a lot more like the ordinary atmospheric distortions often seen near the horizon. Still, Hartung's hypothesis has made its way into many astronomy books and articles. It proved difficult to confirm or refute because data on Giordano Bruno and its surroundings were limited.
Now a new analysis demonstrates that a cratering event could not have happened in 1178. Paul Withers (University of Arizona) finds that an impact large enough to create a 22-km crater would likely have showered Earth with 10 million tons of ejected fragments -- perhaps a trillion bright meteors in all -- during the days that followed. "A meteor storm as impressive as this and lasting for a week would have been considered apocalyptic by all medieval observers," Withers comments. Yet no mention of such displays appears in English, European, Arabic, or Asian chronicles of the era.
Laser-ranging experiments during the 1970s revealed that the Moon nods back and forth by a tiny amount ("free libration"), suggesting to Hartung's supporters that the globe was still reverberating from the impact. But Withers notes that a reanalysis of the laser-ranging data later showed that the slight oscillation arises instead from fluid motions deep in the lunar interior. Furthermore, while Giordano Bruno is indeed the youngest crater of its size anywhere on the Moon, multispectral images from the Clementine spacecraft show that this impact site has to be much older than 800 years. Details of Withers's analysis will appear in the April issue of Meteoritics.
Copyright 2001 Sky Publishing Corporation.
Above is described recent work indicating that the lunar crater Giordano Bruno could not very well have been formed in 1178, which is an interpretation often quoted for the report by Gervase of Canterbury that five men witnessed an event on the Moon that might have been an impact.
Alan Harris of JPL wrote that "I am pleased to see yet another "debunking" of this old Hartung chestnut". But he notes that a similar argument was made 8 years ago, that if a large lunar impact had occurred in 1178 there would have been an associated meteor storm when the ejecta reached the Earth. Harris continues: Regarding the Giordano Bruno claim, I pointed out (Harris, JGR 98, 9145-9149, 1993) that "our final conclusion must be, even in the extraordinarily unlikely event that such a compact clump of ejecta were injected into heliocentric orbit from the Moon, perturbations from the Earth would have quickly dispersed the clump [so that] annual showers of more or less constant intensity should be expected. . . Either by initial dispersion in the velocity or by subsequent perturbations, an event such as Hartung proposes [the Giordano Bruno impact] should have the result that the sky would really light up every midsummer for a week or two." The bottom line is, I agree completely with Withers that there should have been an "apocalyptic" level meteor storm in the days following the claimed event, but furthermore it should have been followed by a pretty spectacular meteor storm on each anniversary since then.
Benny Peiser commented in CCNet for March 19 as follows: "Not so fast, my friend. While I agree that the Giordano Bruno crater appears to be too large indeed to be convincingly associated with a hypothesised lunar impact in 1178, neither Gervase's report nor the possibility of an observed impact on the Moon - and not even the speculation about a link with the Taurid meteor stream have been "debunked." As Ed Vega rightly stresses, it's Carl Sagan's (and others') association of the eyewitness report with the Giordano Bruno crater that has been "debunked", not the report and its impact- interpretation itself. BJP"
In reply to Peiser, I believe that in the absence of physical evidence (such as a young lunar crater), the report from Gervase of Canterbury has little weight. The report is already inconsistent internally with an impact on the Moon, since it says that "this phenomenon was repeated a dozen times or more, the flame assuming various twisted shapes and then returning to normal. Then, after these transformations, the Moon from horn to horn, along its whole length, took on a blackish appearance". The above does not sound to me like the description of an impact. The story held some credibility only because of the claimed association with crater Giordano Bruno. Each person makes his or her own judgement about the veracity of ancient documents, but for me the debunking of the association of this 1178 report with any physical evidence on the Moon effectively undercuts the entire connection of Gervase's report with NEO impacts.