Öz The Vatican Library manuseript (Vat. Pers. 9)1 summarized belovv is a letter containing thc Persian translation of a Latin booklet on Tycho Brahc’s system. It was vvritten by Petrus della Valla, in 1624 from the city of Goa in India, to Mawlânâ Zayn al Dîn-i Lârî (from Lâr in Iran) entitled Al Munajjim, i.e., thc Astronomcr. The author of the Latin original is given as Christophorus Borrus, a Jcsuit pricst and astronomcr from Milano, and it was Petrus della Valla who translated it into Persian. The present manuseript is accompanied by an Italian translation, thc translation of each page being given on the pagc facing it. This copy of thc original letter was probably transeribed and translated by Petrus della Valla himself, who was also from Milano. The Ita- lian translation bcars the date 1631, and thc place of translation is indicatcd as thc city of Romc.