Few records of astronomical observations have survived from the distant past and this is especially true of Western sources. The best prospect for ancient sources was the library at Alexandria in Egypt founded in the third century BC. At its height the library housed about 500,000 rolls, "the equivalent, perhaps, of 100,000 modern books" (Hornblower & Spawforth 1996). Its archives may well have included astronomical observations because Eratosthenes, the famous astronomer and geographer, had once been chief librarian there. Its books might have documented a continuous catalogue of historical observations from 300 BC onwards, including, perhaps, the original eyewitness accounts. But all the books of this library were deliberately destroyed in 641 during the Islamic conquest. The tragic result is that only a few comet appearances have been preserved in Greek and Roman historians and they are "quite incidental, mentioned only as a portent of some great historical event" (Barrett 1978).
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