Inventory no. 52209 - Epact entry
Epact number: 25985
Signed by Egnatio Danti
circa 1570; Florence
Gilt brass; 410 mm in diameter
This magnificent gilt instrument is one of the finest Italian astrolabes to have survived from the Renaissance. There are no separate plates, but a projection for the latitude of Florence has been engraved in the mater. Engraved there is the name of the celebrated cosmographer Egnatio Danti. Danti was an astronomer and cartographer in the service of Cosimo I de' Medici, Grand Duke of Tuscany. In a book on the astrolabe, published in Florence in 1569, he recommends the type of universal projection found on the back of this instrument, and also advises the reader to make one in order to understand it fully.
Some of the features of this astrolabe, such as Mediterranean wind names at the cardinal points on the limb and an adjustable scale of Italian hours, are not common, but are appropriate to an Italian instrument.
Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 52,209
Mater with rim riveted to the back plate. Shaped and decorated throne with shackle and suspension ring. The limb has a scale of degrees that serves both for hours and altitudes. An outer set of numbers makes a scale of degrees 90 to 0 to 90 to 0 to 90, divided to 10, subdivided to 5 and to 1, numbered by 10. An inner set of Roman numerals 0 to XII twice makes a scale of hours divided to 1 hour, subdivided to 20 and to 4 minutes, numbered by 1 hour. Within the limb a moveable ring has an adjustable scale for Italian hours, 0 to 12, divided to 1 hour, subdivided to 20 and to 4 minutes, numbered by 1 hour. The cardinal directions are marked 'OSTRO', PONENTE', TRAMONTANA' and 'LEVANTE'.
The inside of the mater is engraved with a latitude plate for 'G.43 M.40' appropriate to Florence. There are azimuths for every 5 degrees, numbered by 10, and almucantars for every 2 degrees, numbered by 6, meridian line, east-west line, tropics, equator, and crepuscular line. There are lines for equal hours below the horizon, numbered 1 to 12 by 1, and lines dividing the houses of heaven with Roman numerals I to XII by 1. Engraved coat of arms and '·F· EGNATIVS DANTES·'.
Rete for 31 named stars, with bands for the tropics and equator as well as the ecliptic. The meridian band is counterchanged 6 times, the east-west band 8 times and broken twice. The ecliptic band is pierces twice for star positions. It has the names and symbols of the signs, each with a 30-degree scale, divided to 10, subdivided to 5 and to 1, numbered by 10. The equatorial band has an incomplete degree scale from the vernal equinox 0 to 360, divided to 10, subdivided to 5, numbered by 10.
The back has an outer degree scale 0 at the throne to 90 to 0 to 90 to 0. Rojas universal projection with right ascension arcs marked with hours 1 to 12, 'HORE ANTE MERIDIAM', above the Tropic of Cancer and 12 to 1, 'HORE POST MERIDIEM', beneath the Tropic of Capricorn. Between the tropics are lines of declination for every 5 degrees of the zodiac, with symbols for the signs. Whole hour lines and the beginning of each sign are marked by added dots. A number of named stars are marked on the projection. A diametric line is drawn for the ecliptic.
A pair of rules, are provided for the universal projection: a diametric rule with a linear scale for degrees, 0 at the centre and returning to the centre at 180 and 360, divided to 10, subdivided to 5 and to 1, numbered by 10, and a half-diameter with a sliding joint in the shape of a grotesque head, with a scale 0 to 90 to 0 in either edge, divided to 10, subdivided to 5 and to 1, numbered by 10. Decorated alidade with pin and slit sights. Pin attached to the diametric rule and wedge.
See R. T. Gunther, The Astrolabes of the World (2 vols, Oxford, 1932), vol. 2, pp. 332-3 and G. L'E. Turner, 'The Florentine Workshop of Giovan Battista Giusti, 1556-c.1575', Nuncius, 10 (1995), pp. 131-72.