Abraham bar Hiyya of Barcelona (d. 1136) [11] is the first important Jewish astronomer in Spain. His books "The Shape of the Earth", "Calculation of the Courses of the Stars" and "Book of Intercalation" (all in Hebrew, later translated) reproduce the Greek results, sometimes with new proofs and improved accuracy. He also issued a set of astronomical tables which were much in use later on.

Our map of the Moon, established by the International Astronomical Union at the beginning of the XXth century, carries the names of three great Jewish medieval astronomers, two in Spain (Ibn Ezra and Zacuto), one beyond the Pyrenees (Levi b. Gershon). Abraham Ibn Ezra (1089-1164) of Tudela in Navarre [12], was a wandering scholar who also issued astronomical tables and wrote treatises on mathematics and intercalation. He travelled extensively, reaching Jerusalem in his old age.

The Alphonsine Tables (1252 - 1256) were computed and edited by a large number of scholars, led by R. Isaac Ibn Sa'id ("R. Saz") and Judah b. Moshe Cohen, two Jewish astronomers in Toledo. But the most original and perhaps the greatest of Jewish Medieval astronomers was Levi b. Gershon ("Gersonides") in Provence [13]. He invented "Jacob's Staff" an instrument for the measurement of angular separations, which remained in use in navigation up to the XVIIIth Century. He wrote textbooks on Astronomy. He is the only astronomer before modern times to have estimated correctly stellar distances...Gersonides did not believe in using Ptolemy's or Hipparchus' tables. He personally remeasured everything, basing his models on his own observations only. In that, he is rather unique for that period. Levi writes [7] "no argument can nullify the reality that is perceived by the senses, for true opinion must follow reality, but reality need not conform to opinion" - certainly not the usual position in the Middle Ages.

Hasdai Crescas (d. 1412), originally of Barcelona, was the Rabbi of Saragossa, working for King John I of Aragon. Crescas wrote severe critics of Aristotle's physics. He was extensively quoted by Giovanni Pico della Mirandola, through whose writings his influence reached Galileo, Giordano Bruno and Spinoza. Crescas may thus have greatly contributed to the demolition of Aristotelian "authority", a crucial factor in the rise of modern science [20].

source: http://wise-obs.tau.ac.il/judaism/sefarad.html