18 June 1178 (Julian calendar)
In this year, on the Sunday before the feast of St. John the Baptist, after sunset when the moon has first become visible, a marvellous 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 towards 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... Then after these transformations the moon from horn to horn, that is along its whole length, took on a blackish appearance.
One (controversial) interpretation of this narrative, first suggested by Dr Jack B Hartung some 800 years later, is that it is a description of a crater impact in progress. The "upper horn split in two" is the apparent effect of a plume of dark dust or vapour, the "flaming torch [of] hot coals and sparks" describes the molten ejecta, and the way in which the rest of the Moon "writhed", "throbbed" and eventually "took on a blackish appearance" could be the effects of a temporary lunar atmosphere of gas and vapour created by the impact.