George of Austria (1505-1557), like Nicolas Perrenot on the terrestrial globe, was a great figure of his time. A natural son of Emperor Maximilian I, he began his ecclesiastical career in 1525 as Bishop of Brixen. In 1541 he was appointed Prince-Bishop of Liège by Emperor Charles V, who wanted a devoted clergyman in this strategic position.
Ampliss[imo] Praesuli Principiq[ue] ill[ustrissi]mo Georgio ab Austria Dei dispositione Episcopo Leodiensi, Duci Bullonensi, Marchioni Fracimotensi, Comiti Lossensi, etc, mecoenati optime merito dd. Gerardus Mercator Rupelmondanus.
Inhibitum est ne quis hoc opus imitetur, aut alibi factum vendat, intra fines Imperii, vel prouinciarum inferiorum Caes. M[aiesta]tis ante decennium, sub poenis et mulctis in diplomatibus cotentis. Obernburger & Soete subscrib[unt]
Louanij anno Domini 1551 mense Aprili
In his representation of the constellations and their nomenclature, Gerardus Mercator produced the most comprehensive celestial globe of the 16th century. These representations included figures from literary tradition inspired by Greek sources. In this respect, the German-Flemish cartographer sometimes seems less of an astronomer than a man of the Renaissance who selected his sources with a critical eye.
Each constellation is indicated with its Latin and Greek names, with an added transliteration of its Arab name (or what was meant to be Arabic in the 16th century). Mercator must have consulted several sources for his nomenclature and, on the face of it, proceeded in encyclopaedic fashion. His knowledge of astronomy came from books, not from observations.
Mercator’s Pleiades
Modern representation of the Pleiades. Source : stellarmap.com
Pleiades
The Pleiades cluster has been known since Antiquity. Some of its stars can be seen with the naked eye. Only four of them are described in Ptolemy’s star catalogue and its offshoots. The Mercator’s globe presents seven stars.
Portfolio of constellations
Mercator took great care to make his globes useful. While the pamphlets that originally accompanied them have been lost, the cartographer discusses the numerous applications of his celestial globe in a copy of Declaratio insigniorum utilitatum found in Milan. By explaining certain ways of handling his celestial globe, he tells his contemporaries that it can be used :
- to find out the “quantity of day”, i.e. the latitude and times at which the Sun rises and sets ;
- to recognise the stars in the sky, even without the least prior knowledge ;
- to provide the wherewithal to measure how high a star or the Sun stands above the horizon and the Sun’s distance below the horizon ;
- to indicate the time it takes for a star to complete its course above the horizon, from the time it rises to the time it sets ;
- to determine the meridian of a place ;
- to find the latitude of a country ;
- to situate the sign and degree of the Zodiac where the Sun is located ;
- to determine the time of year when a star will pass the meridian at midnight ;
- to determine the time when a star will reach the meridian ;
- to determine when twilight will fall.
Find out more
- Union Astronomique Internationale / International Astronomical Union
- Aujac, G. (1976) « Le ciel des fixes et ses représentations en Grèce ancienne », in : Revue d’histoire des sciences, Vol. 29, N° 4, pp. 289-307 [URL].
- Dekker, E., Krogt, P. van der (1994) « Les globes », in : Watelet, M. (1994), pp. 242-267.
Dekker, E. (2013) Illustrating the phaenomena : celestial cartography in Antiquity and the Middle Ages, Oxford : Oxford University Press. - Whitfield, P. (1995) The Mapping of the Heavens, London : The British Library.
- Woodward, D. (2007a) Cartography in the European Renaissance, « The history of cartography » (J.B. Harley & D. Woodward, eds.), Vol. 3, Chicago : The University of Chicago Press, Parties I-3, I-4, I-5, pp. 53-173.
Mercator’s celestial globe is surrounded by a brass meridian capped at the North Pole by a time dial (absent on the Lausanne copy) and a horizon ring indicating the main religious holidays and their dates along with the twelve signs of the Zodiac for astrological forecasts.
The sphere is covered with twelve gores extending to the 70th parallels, with each polar region capped by a round calotte. The celestial gores are aligned with their equatorial coordinates rather than the coordinates of their ecliptic. They meet at the celestial poles, which thus coincide with the axis of the globe’s base.
A large part of the area around the South Pole is blank, which is no surprise since it could not be seen from the latitudes of Europe. Thus, stars with a declination exceeding an absolute value of 66°30’ are missing. The constellations are named in Latin and Greek with an Arabic transliteration
Mercator’s globe shows a precession correction of 20°55’, in line with the theory of Nicolaus Copernicus. The equator and ecliptic are graduated with the degrees numbered on them by tens. The prime meridian runs just next to the tail of Pisces, shown below the wing of Pegasus.
The horizon ring, or rational horizon, is divided width-wise into two halves :
- the inner half, from inside to outside, indicates the ring’s division into degrees, the signs of the Zodiac, the days and months of the Roman calendar, the main religious holidays and the main winds in the different seasons ;
- the outer half indicates astrological forecasts, a trace of Arab astrology which still had its followers in the 16th century. Historians suppose that in including them Mercator must have made a concession to popular beliefs.
© Royal Library of Belgium, reproduced with permission
The relative shapes and dimensions of individual stars are shown in six different sizes along with the nebulae. A list of models is given near the top of the globe, above the constellation Gemini.
Apart from the Milky Way and a large number of stars not belonging to symbolic asterisms, Mercator included nearly all of Ptolemy’s 1022 stars (according to J. van Raemdonck there are 934) spread across 51 constellations, compared with the 48 constellations commonly referred to since Antiquity. Among the additional representations we can find :
- Antinous, made up of twelve stars, situated in the southern hemisphere below the feet of Orion ;
- Lepus, made up of twelve stars, situated in the southern hemisphere below the feet of Orion ;
- Cincinnus (Caesaries, Berenicis crinis, Trica), made up of one star and two nebulae and located in the northern hemisphere under the tail of Ursa Major (the Plough). Coma Bernecis (Berenice’s Hair) has been on the official list of constellations since 1930 ;
- Canicula (Almogelsa, Alschere, Procyon) is situated in the northern hemisphere below the tail of Cancer, its correct position, contrary to the location in the southern hemisphere assigned to it later by Jocodus Hondius.
]]>