As yet, Gervase, though one of the senior monks, had held no prominent office, but about this time he was made sacristan, for in 1193 he attended the new archbishop, Hubert Walter, in that capacity.
Five witnesses from Canterbury reported to the abbey's chronicler, Gervase, that shortly after sunset on 18 June 1178, they saw "the upper horn [of the moon] split in two."
Furthermore, Gervase writes, "From the midpoint of the division a flaming torch sprang up, spewing out, over a considerable distance, fire, hot coals and sparks.
Modern theories predict that a (conjectural) asteroid or comet impact on the Moon would cause a plume of molten matter rising up from the surface, which is consistent with the monks' description.
(3) Actus Pontificum Cantuariensis Ecclesia, a history of the archbishops of Canterbury to the death of Hubert Walter in 1205, also printed by Twysden with the chronicle.
A play by Dorothy L. Sayers, The Zeal of Thy House is based on Gervase's account of the injury and resignation of William of Sens.