An Astrolabe by Michiel Coignet

Astrolabes by Michiel Coignet are rare. So far only four have been recorded: 1572 (now in Berlin), 1598 (now in Madrid), 1601 (now in Leiden) and an undated one in Hamburg which is particulary relevant in the Ximenez context. It features inside the fretted rete a monogram with an interwoven 'A' and 'I', for Albrecht and Isabella. The archdukes in whose service Coignet worked between 1596 and 1623.

The Ximenez inventory mentions an astrolabe that contained five latitude plates of 'laminas.' An astrolabe consists of five essential parts: first, a set of latitude plates representing the terrestrial sphere, second, a rete representing the celestial sphere, third, a mater to hold the rete and plates together, fourth, an alidade to measure height and fifth, a ring to support the astrolabe. The set of various latitude plates - usually between one and five - features an engraved stereographic projection of one particular latitude on each side. An astrolabe with five plates could thus be operated in ten cities with different latitudes. If one would, for example, make observations in Antwerp, one would need to put the latitude plate for 51° underneath the rete, but in Madrid a plate with a projection for 40° would be necessary. None of the four preserved Coignet astrolabes features five plates, but it can be assumed that the now lost Ximenez astrolabe by Coignet would have been equipped with latitude plates for Southern cities in Portugal and Spain.

Koenraad Cleempoel, University of Hasselt

Planispheric astrolabe with the monogram of Archduke Albrecht and Isabella inside the rete, attributed to Michiel Coignet, c. 1615, Museum für Kunst und Gewerbe, Hamburg. Image: © Museum für Kunst und Gewerbe.