Abu Saeed Sijazi or Sijzi

Abu Saeed Sijazi or Sijzi (945-1020 AD) was an astronomer, mathematician and astrologer. His last name indicates that he was a native of Sijistan, what is now called Sistan, a border region of today’s eastern Iran and southwestern Afghanistan.

Sijzi wrote at least 45 geometrical and 14 astronomical treaties. He dedicated much of his work to the prince of Balkh, and Fanna Khosrow, the emir of the Buyid dynasty, who seems to have been his patron. He worked for years in the city of Shiraz in Iran making astronomical observations. He combined data from pre-Islamic material, specifically from the Iranian Sassanid dynasty era, and from the Islamic era including Harun al-Rashid’s for a book on general astrology and its history. He is best known for his correspondence with well-known scientist and philosopher, Biruni, and for proposing in the 10th century that the Earth rotates around its axis.
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Biruni writes about Sijzi that, “I have seen the astrolabe called Zuraqi invented by Abu Saeed Sijzi. I liked it very much and praised him a great deal, as it is based on the idea entertained by some to the effect that the motion we see is due to the Earth's movement and not to that of the sky. By my life, it is a problem difficult of solution and refutation. [...] For it is the same whether you take it that the Earth is in motion or the sky. For, in both cases, it does not affect the Astronomical Science. It is just for the physicist to see if it is possible to refute it.”

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Sources:

• Seline, Helaine. "Encyclopedia of the History of Science, Technology and Medicine in non-Western countries.
• Wikipedia. Al-Sijzi. CC SA BY
• Photo: By Jacopo Koushan (User:Jacopo188)Photograph by Masoud Safarniya (User:M.safarniya) - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=26080692