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When Galileo observed the belt and sword of Orion the Hunter, and the Pleiades star cluster on the back of Taurus the Bull, the background of night gave way before his eyes: His telescope resolved an astonishing number of unexpected stars never seen before. 

On one page he shows 36 new stars around the original six of the Pleiades, and on another, 80 new stars near the belt and sword of Orion. What if uncountable stars might exist, much farther away than was previously believed? How plausible would it be for an immense and vastly thick sphere of stars to rotate every 24 hours around a tiny central, stationary Earth?

“For the Galaxy is nothing else than a congeries of innumerable stars distributed in clusters. To whatever region of it you direct your spyglass, an immense number of stars immediately offer themselves to view, of which very many appear rather large and very conspicuous but the multitude of small ones is truly unfathomable.”
Galileo, Sidereus Nuncius
trans. Albert Van Helden (University of Chicago, 1989).

In contrast to the constellation figures in Hyginus and Abu Ma’shar, Piccolomini created a star atlas, measuring the positions of the stars according to an indicated scale (specific to each plate). He designated stars by Roman letters (a, b, c, etc.) in order of apparent brightness. Piccolomini also indicated brighter stars by showing them larger on the page. 

Piccolomini, at the University of Padua at this time, published a number of works in the vernacular. His wrote an introduction to astronomy, The Sphere of the Universe (La Sfera del Mondo), in the Tuscan dialect. The 1st edition of La Sfera is included in this volume; 14 editions were published before the end of the century. Piccolomini was particularly interested in codifying the use of standard scientific terms in Italian, creating them when necessary, especially in astronomy.

Compare Piccolomini’s depiction of Orion with Galileo’s, who also declined to include a constellation figure.
Piccolomini’s plates are numbered according to Ptolemy’s list of 48 constellations, although the plate for Equuleus the Little Horse is missing from this and other known copies.

Constellation figures were not the only conceptual entities Piccolomini omitted: he was also skeptical of the reality of the geometrical devices used in astronomical systems, despite their effectiveness as calculation tools. For example, Ptolemy could model the motion of the Sun using either an epicycle or an eccentric model; these models could both provide accurate predictions of the Sun’s positions, but both could not be true. For Piccolomini, mathematical methods did not rise to the level of logical demonstrations.

Piccolomini was an advocate not only of science in the vernacular, but also of providing educational opportunities for women.

For this first edition of Ptolemy’s collected works, Johann Honter drew constellation figures after the manner of Albrecht Dürer. The figures appear in contemporary dress rather than in a classical style. Although positioned on a grid, unfortunately the coordinates were misaligned and constellations are shifted by 30°.

Ptolemy (Claudius Ptolemaios) lived in Alexandria, Egypt, in the second century. Ptolemy’s technical work on astronomy, originally written in Greek, was titled Almagest (”The Greatest”) by its Arabic translators. Ptolemy’s Almagest represents the culmination of ancient Babylonian and Greek mathematical astronomy. It achieved an unparalleled degree of accuracy in quantitative predictions of the positions of the planets.

Additional source available at https://repository.ou.edu/uuid/80af71d1-8942-5381-ac16-8b036e3447e0?sol…;