Si credeva perduto per sempre. Invece il più antico catalogo di stelle è riemerso da una pergamena medievale del monastero di Santa Caterina in Egitto grazie all'intuito di alcuni ricercatori e alla tecnologia. La "mappa", risalente al 129 a.C., è stata compilata dal grande astronomo greco Ipparco.
La pergamena con il testo originale
La scoperta, pubblicata sul Journal for the History of Astronomy, si deve al Centro nazionale francese per la ricerca scientifica. Il manoscritto medievale, le cui pagine si trovano ora nel Museo della Bibbia di Washington (USA), contiene una raccolta di testi siriaci scritti nel X-XI secolo, ma si tratta in realtà di un palinsesto: un testo più antico era stato raschiato via da uno scriba per riutilizzare la pergamena.
L'immagine multispettrale rivela il testo sottostante in greco
Dal 2017 le pagine sono state analizzate con fotografie fatte in varie lunghezze d'onda e utilizzando algoritmi informatici, per far riemergere il testo nascosto.
La restituzione, in giallo, del testo di Ipparco
In questo modo, alcuni fogli hanno rivelato le coordinate stellari, che hanno permesso di risalire a Ipparco e di datare il periodo delle osservazioni.
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