Alessandro Piccolomini’s star atlas

In 1540 the Italian astronomer Alessandro Piccolomini (1508–79) published a handbook of astronomy called De le stelle fisse (On the fixed stars) which contained charts for 47 of the 48 Ptolemaic constellations, with stars down to 5th magnitude taken from the catalogue in the Almagest. (Equuleus was the constellation missed out, presumably because it had no stars bright enough for inclusion – Ptolemy had listed only four stars in it, all of which he described simply as ‘faint’). Although quite crudely drawn, Piccolomini’s set of charts is generally regarded as the first true star atlas, as distinct from the single-sheet hemispheres drawn by Albrecht Dürer and his followers. Written in vernacular Italian rather than scholarly Latin, Piccolomini’s De le stelle fisse proved highly popular and went through more than a dozen editions over the following decades, often bound with another astronomical work of his, De la sfera del mondo (On the sphere of the world).

Whereas Dürer had numbered the stars of each constellation in the order they appeared in Ptolemy’s catalogue, Piccolomini labelled the brightest members with lowercase Roman letters (although with three exceptions: on the charts of Ursa Minor, Perseus, and Cetus the stars are labelled with capitals. The reason for this inconsistency is unknown, but could simply be a printer’s error.) Piccolomini’s  innovation was a forerunner of the more extensive system of Greek letters that Johann Bayer was to use over 60 years later in his Uranometria atlas of 1603.

Piccolomini’s constellations were drawn face-on as they appear in the sky, rather than the mirror-image globe view of Dürer, which made the atlas more readily usable by observers. Four different sizes of star symbol were used, indicating the stars’ brightnesses from 1st to 4th magnitude as estimated by Ptolemy, although in some constellations Piccolomini included 5th-magnitude stars to make up the shape. In all, his charts plotted 621 stars. In the handbook he provided descriptions of each constellation and a mini-catalogue of the 455 brightest stars.

However, Piccolomini’s charts had many weaknesses. For one, north is not always at the top; the figures seem to have been turned whichever way they fitted best on the page. There were no coordinates for orientation; instead, north is indicated by the words ‘Parte verso il polo’, i.e. towards the pole, and the words ‘verso dove’ (towards) and ‘donde’ (whence) were added in the corners to indicate how the constellation turned as the sky rotated. Another drawback was that the charts were drawn to different scales, depending on the size of the constellation. An all-sky key chart to show the constellations in context would have been helpful, but there was none.

Piccolomini’s charts lacked the mythical constellation figures that made the planispheres of Dürer and Apianus so visually appealing, and despite their popularity at the time they had no influence on the magnificent pictorial atlases by Bayer, Hevelius, Flamsteed, and Bode that were to follow.

© Ian Ridpath. All rights reserved