Johannes Honter’s celestial hemispheres
Johannes Honter’s celestial hemispheres of 1532 were the first printed star charts to show the sky from a terrestrial viewpoint, rather than as on a sphere. Like the Dürer maps before them, Honter’s hemispheres are centred on the ecliptic poles, not the celestial poles, so the constellations of the zodiac lie around the rim. Honter repeated the zodiacal figures on his southern hemisphere chart, which Dürer did not. Honter’s hemispheres were 25 cm (9.8 inches) in diameter, some 10 cm smaller than Dürer’s.
(Images courtesy Daniel Crouch Rare Books)
Johannes Honter (1498–1549), a theologian and cartographer from Transylvania (the modern Romania), published a pair of celestial hemispheres in 1532 with what was then a novel feature: they showed the constellations the right way round, as they appear in the sky. This might seem obvious to us now, but at that time astronomers were more familiar with globes than printed charts.
Dürer, Apianus, and their imitators had produced charts that depicted the constellations as they appear on the surface of a celestial globe, but the drawback was that the figures were mirror images of the way we see them from Earth. After Honter, the advantage of drawing the constellations the right way round became self-evident, although there were a few hold-outs such as Johannes Hevelius who still showed the constellations in globe view on his star atlas, Firmamentum Sobiescianum, a century and half later.
Another distinctive feature of Honter’s charts is that several of the constellation figures are clothed in contemporary European dress, unlike the classical nudes of Dürer and his followers – see, for example, Ophiuchus, Boötes, and Auriga (here named Erichthonius).
Honter’s charts first appeared in 1532 but were later reprinted a number of times, most notably in an edition of Ptolemy’s collected works, Omnia quae extant opera, published in 1541, and editions of Aratus’s Phaenomena in 1559 and 1576. Hence they were probably more widely seen at the time than Dürer’s charts, even though they are less well-known today.
However, Honter’s maps suffered several flaws that would have restricted their usefulness to serious astronomers. For a start, he did not number the stars, which Dürer had done, so they could not easily be looked up in the Almagest catalogue. More seriously, the vernal equinox is shown as lying in the front part of Aries, whereas by Honter’s time it had moved into western Pisces, a difference in celestial longitude of some 30 degrees. And in a strange plotting error, Polaris is misplaced by about 20 degrees to the east, along with the rest of Ursa Minor, giving an odd look to the north polar region. Honter would have benefited from an astronomical advisor like the one Dürer had.
© Ian Ridpath. All rights reserved
