Astronomy · a Light

He argued nothing observable rules out a turning earth

Ali Qushji learned his astronomy at Ulugh Beg's observatory in Samarkand and worked on its star tables. After Ulugh Beg was killed in 1449 he moved west, and in the early 1470s Mehmed II brought him to Istanbul to teach. He made two arguments unusual for his time. The first was that astronomy does not need Aristotle's physics underneath it and should be built on observation and geometry alone. The second followed from it: everything seen in the sky would look the same whether the earth stands still or turns, so observation cannot settle the matter, and no astronomical result requires a motionless earth. He did not claim the earth moves. He said the case that it does not was weaker than people assumed.

Ali Qushji · Samarkand and Istanbul, died 1474