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Attributed to Giovanni Battista Giusti
Later 16th century; Florence
Brass and wood; 840 mm in diameter

Only one side of this very large astrolabe bears markings. The stereographic projection is calibrated for the latitude of Florence, as shown by the inscription 'G. 43 M.40'. The projection includes the astrological houses, the unequal hours, the twilight line, the tropics and the equator. Around the limb of the astrolabe, starting from the outside, are the names of the eight winds: 'OSTRO, LIBECCIO, PONENTE, MAESTRO, TRAMONTANA, GRECO, LEVANTE, SCIROCCO'. These are accompanied by divisions into twenty-four hours, the degrees of the zodiac subdivided into divisions of three minutes of arc by cross-lines, the symbols for the signs of the zodiac, a shadow scale and the calendar. The alidade is counterchanged and bears no markings. The instrument is equipped with pinhole sights.

The rete of the instrument is made up of the circles of the equator, the ecliptic and both tropics. Because of the large diameter of the rete, a pattern of strapwork links the circles, forming twists and loops. The instrument is table-mounted. It was displayed in the Stanzino delle Matematiche of the Uffizi Gallery, then in the Stanza delle Matematiche of the same Gallery, and, finally, in the Reale Museo di Fisica e Storia Naturale. Because Galileo used the instrument, it has become associated with his name. The astrolabe was previously attributed to Egnatio Danti, but has been more recently attributed to Giovanni Battista Giusti.

See G. Righini, "Il grande astrolabio del Museo di Storia della Scienza di Firenze", Annali dell'Istituto e Museo di Storia della Scienza di Firenze, 2 (1977), at pp. 45-66; M. Felli, L'astrolabio di Galileo (Florence, 1983); G. L'E. Turner, "The Florentine workshop of Giovan Battista Giusti", Nuncius: Annali di storia della scienza, 10 (1995), pp. 131-72, at pp. 157-160.

Mara Miniati

Istituto e Museo di Storia della Scienza, Firenze
Inventory no. 3361

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