Norman describes Piccolomini as "an early popularizer of science who wrote his astronomical treatises in the vernacular in order to extend scientific knowledge beyond the confines of church and university. His De la sfera del mondo ... is a remarkable exposition of the traditional Ptolemaic-Aristotelian geocentric cosmography, but its appendix, De le stelle fisse, represents the first printed star atlas, containing maps of the stars as opposed to simple pictures of constellations, and introducing the practice of identifying stars by letter, a method later adopted and expanded by Bayer."