THE ORIGIN OF THE LUNAR
CRATER GIORDANO BRUNO
An incredible eyewitness event which occurred on the Moon on June 18, 1178 was investigated by Jack Hartung, a State University of New York astronomer in a paper published in Meteoritics, The Journal of the Meteoritical Society, for September, 1976. Quoted from the Medieval Chronicles by a writer known as Gervase of Canturbury, “the upper horn of the new moon seemed to split in two and a flame shot from it." Hartung's investigation of the event led to the current translation of the episode:
In this year, on the Sunday before the Feast of St. John the Baptist, after sunset when the moon had first become visible a marvelous phenomenon was witnessed by some five or more men who were sitting there 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 of this division a flaming torch sprang up, spewing out, over a 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 returned to its proper state. This phenomenon was repeated a dozen times or more, the flame assuming various twisting shapes at random and then returning to normal. Then after these transformations the moon from horn to horn, that is 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 addition or falsification in the above narrative.
The event reported in 1178 appears to be unique. Although a wide variety of short-duration events or transient lunar phenomena (TLP’s) have been reported by observers of the Moon, no similar event of the magnitude and complexity observed has ever been described. Only this past November 17, 1999 did astronomers finally have the proof of objects striking the Moon: Visual and video confirmation of some Leonid meteors impacting the Moon.
A variety of hypotheses may be advanced to explain the 1178 phenomena observed. The fact that five men were "prepared to stake their honor" leads one to believe that something was observed and that the report was not entirely, the product of someone's imagination. The events described may have originated in the atmosphere of the Earth as a result of cloud layers or turbulence just above the western horizon or the entry of a meteor along the line of sight to the Moon. However, the report seems credible, since it repeatedly refers to the Moon and never mentions clouds or the sky or anything not related to the Moon.
Such an event on the Moon must have had either an external (impact) or internal (volcanic) origin. From the report alone it may not be possible to explain the origin of the phenomena observed. However, with our present understanding of the lunar surface and processes occurring in the Solar System, the description is consistent with the occurrence of a very large impact on the lunar surface.
From the translation, "The upper horn (of a new Moon) split in two." A portion of the sunlit crescent visible at the earth was either obscured by the ejecta cone or cloud produced by the impact or darkened by the shadow of the ejecta.
"A flaming torch sprang up, spewing out fire, hot coals, and sparks." Incandescent gases and solids or liquids were ejected. "The moon ... writhed ... and ... throbbed like a wounded snake." Gases produced or released by the impact formed a temporary atmosphere which was in turbulent or had non-uniform motion, thus causing the light from the moon to pass through variable amounts of material with variable indices of refraction.
"Afterwards it (the crescent moon) resumed its proper state. This phenomenon was repeated a dozen times or more, the flame assuming various twisting shapes at random and then returning to normal." Evidently, "the flame" continued throughout the writhing process, which can be attributed to the large-scale motion of gas clouds. Because the duration of a "flame" consisting of incandescent gases or other material among the ejecta should be short compared to the time scale for the motion of large gas clouds, some uncertainty exists regarding the interpretation of "the flame." Instead of consisting of incandescent material, the appearance of a "flame" could be produced by sunlight reflected from dust particles moving as ejecta from the crater, just after the impact.
"Then ... the moon from horn to horn, that is along its whole length, took on a blackish appearance." This observation is consistent with the presence around the entire moon of a temporary atmosphere in which a sufficient amount of dust was suspended to block a significant amount of light reflected from the moon's surface.
The most decisive test of the validity of the report and the impact hypothesis explaining it would be the identification of a surface feature on the Moon which corresponds to the event reported. The occurrence of the event at the "midpoint" of the "upper horn" of a "new Moon" establishes its location at a latitude near 45° north and longitude near 90° east.
The size of the event may be estimated based on the fact that the observations were made by human eyes without optical aids. If the event was just visible to the unaided eye, then the smallest shadow on, or ejecta cloud above, the Moon that could have been observed at the Earth would have had a linear dimension of about 40 km. Based on this the Hartung estimates that the ejecta cloud and the shadow actually observed would have had linear dimensions in excess of about 100 km; the diameter of the resulting crater would exceed 10 km; and the bright rays associated with such a recently formed crater would extend at least 100 km from the crater.
Does a crater corresponding to the medieval observations and our interpretations and estimates actually exist on the Moon? The criteria used in search of the actual crater formed 821 years ago are that the crater must have a:
1. selenographic latitude between 30° and 60° N.
2. selenographic longitude between 75° and 105° E.
3. diameter greater than 10 km.
4. surrounding pattern of prominent bright rays.
Using Clementine orbiter photography (from the National Space Science Data Center CD-ROM), there is an impressive 20-km-diameter crater at a latitude of 36° North and longitude of 103° East with a very prominent bright rays extending for hundreds of kilometers. Therefore Hartung concluded that this crater is the one formed on June 18, 1178. The crater, known as Giordano Bruno, is shown in Figure 1 below. The impact area on the Moon is shown as Figure 2.
Figure 1. Mosaic of crater Giordano Bruno (arrowed). From Clementine imagery, National Space Science Data Center, 1997. Crater location: 36°North latitude, 103°East longitude.
Not only does Giordano Bruno satisfy the above-stated criteria, but there is independent evidence to suggest it was among the most recently formed large craters on the Moon. The crater is the center of a ray system rivaling that of Tycho, yet its rim diameter is only about one-fifth that of Tycho. The first photographs of Giordano Bruno, made in October 1959 during the Soviet Lunik III Mission, showed a ray system so bright and impressive that the actual crater diameter was over-estimated by a factor of three. Based on a survey of large bright-rayed craters on the Moon, Hartung did not found a single crater with a larger ray-length-to-crater-diameter ratio than that for Giordano Bruno. These observations support the idea that this crater may have been the most recently formed large crater on the Moon.
Figure 2. Location of impact crater Giordano Bruno, as seen by 5 men on June 18, 1178 AD.
Assuming the observation was made in the vicinity of Canterbury, England, (southern England) the Sun would have set at about 8:15 p.m. local Sun time and that the Moon would have set about 45 minutes later. Thus, the event must have occurred between about 20:15 and 21:00 hours, GMT, on June 18, 1178. Modern software programs show the moon in a crescent phase (see Figure 2 above) exactly as the five men described it with the "horns tilted toward the east."
ADDENDUM - From www.Skypub.com, March, 2001
Did medieval residents of Canterbury, England, really witness the creation of a large crater on the Moon in June 1178? The brightly rayed crater Giordano Bruno at upper left has been suspected to be the result of such an impact, however, recent studies have put this scenario into doubt. 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.
J. Kelly Beatty
REFERENCES
Corliss, W., 1979, Mysterious Universe: A Handbook of Astronomical Anomalies, The Sourcebook Project, Glen Arms, Maryland, p. 233.
Hartung, J., 1976, Was the Formation of a 20-km Diameter Impact Crater on the Moon Observed on June 18, 1178?, Meteoritics, 11, No. 3, p. 187.
Wood, C.A., 2000, What's New on the Moon, Sky and Telescope, April 2000, p. 125.