Rufus, W. Carl (May 1939), "The Influence of Islamic Astronomy in Europe and the Far East", Popular Astronomy, 47 (5): 233–238 [236], Bibcode:1939PA.....47..233R[1]
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Rufus, W. Carl (May 1939), "The Influence of Islamic Astronomy in Europe and the Far East", Popular Astronomy, 47 (5): 233–238 [236], Bibcode:1939PA.....47..233R[1]