Abu Sa'id Ahmed ibn Mohammed ibn Abd al-Jalil al-Sijzi (short for al-Sijistani) was a Persian astronomer and mathematician from Sistan. Sijistan or Sistan is a region in the east of current Iran. Its historical name is Sakastan from the name Saka who were East Iranian inhabitants of the region. Sakastan is mentioned in abundance in the Shahnama. Al-Sijzi is thought to have been born around 945 CE, and lived through about 1020. His main scientific focus was astronomy. He had a deep knowledge of… (More on Al-sijzi)