Astronomy · a Light

His eclipse timings were still useful eight hundred years later

Ibn Yunus worked in Cairo under the Fatimids and finished his great set of astronomical tables, the Hakimi Zij, around 1003. What sets it apart is that he wrote down the raw observations, his own and other people's, rather than only the conclusions drawn from them: dozens of planetary conjunctions and about thirty lunar eclipses, each with its date and its measured time, including older records he had dug out of earlier astronomers' papers. Extracts were printed in Paris in 1804, and nineteenth century astronomers used his eclipse times, along with other early records, to test whether the moon's motion around the earth is slowly changing. It is. Ibn Yunus was not answering that question. He simply wrote the numbers down and kept them.

Ibn Yunus · Cairo, died 1009 CE