An ancient instrument, predecessor to the sextant, for observing the positions of heavenly bodies and determining their elevation above the horizon. The astrolabe of Christopher Columbus was on display at the Philadelphia Sesquicentennial. The oldest known example, called "The Mathematical Jewel," is of Persian origin. It was made by Ahmad and Mahud, sons of Ibraham (q.v.) the Astrologer of Isfahan, and is in the Lewis Evans collection in the Old Ashmolean Museum at Oxford, England. The invention is attributed by some to Hipparchus (q.v.) but others credit it to the Arabs, some 400 years prior.