A series of astronomers, beginning with the Muslim astronomer al-Farghānī, used the Ptolemaic model of nesting spheres to compute distances to the stars and planetary spheres. Al-Farghānī's distance to the stars was 20,110 Earth radii which, on the assumption that the radius of the Earth was , came to . An introduction to Ptolemy's "Almagest", the "Tashil al-Majisti", believed to be written by Thābit ibn Qurra, presented minor variations of Ptolemy's distances to the celestial spheres. In his "Zij", Al-Battānī presented independent calculations of the distances to the planets on the model of nesting spheres, which he thought was due to scholars writing after Ptolemy. His calculations yielded a distance of 19,000 Earth radii to the stars.