Object Name: planispheric astrolabe
Dimensions: 18 x 13.6 x 1.7 cm (7 1/16 x 5 3/8 x 11/16 in.)
Description: This planispheric astrolabe is made of gilt brass and silver in an extraordinary two-toned fashion. The mater, rete, and alidade are brass. The single tympan, bolt, washer, horse, suspension ring, and shackle are silver.
The front rim of the mater is marked in hours, 1-12, twice, and divided into 4-minute intervals. In the well of the mater are four holes. Two are plugged. The other two are for securing the tympan (to keep it from rotating).
The back of the mater is ringed in degrees 90°-0°-90°-0°-90°, and subdivided into 2/3° (i.e., into 40' intervals) using the adjacent scale of the zodiacal calendar. Otherwise the divided circle is subdivided into 10/3° units. The zodiacal calendar has Latin names for the signs in abbreviated form, and is divided every 1°. Eccentric to it is another circle for the civil calendar, with months labeled in Latin abbreviations and divisions every day. The upper left and upper right quadrants have lines for unequal hours, 1-6, with divisions by single hours. The lower left and lower right quadrants have a shadow square of 12 parts on each side.
The rete 22 star pointers. A circle marks the ecliptic, which is labeled in Latin abbreviations and divided every 2°. There are partial arcs to indicate the celestial equator.
The alidade is counterchanged and has hinged sights with slits. There is a scale along the alidade for the hours of sunrise and sunset to be used with the eccentric calendar scale. One is "horae ortus" and it is marked 1-9 and divided by 1/2 hours. The other is "horae occasus," which runs 4-12 and is divided by 1/2 hours.
The rule is single and plain.
The bolt is silver with a round head engraved with an 8 pointed star. The washer is silver and engraved wtih a 16-point wind rose. The horse is a silver cotter pin.
The tympan is silver and is contemporary with the rest of the instrument, being engraved by the same hand in the same style as the rest of the astrolabe. It is clearly not a replacement. It is marked "34" for latitude of 34°. The stereographic projection of the local coordinates is marked with azimuths every 10°. Altitudes are indicated every 2° with a circle of running arrows at every 10° interval. Altitudes are labeled on the western side (the left side) 2, 4, 6, 8, 10 only. Below the stereographic projection are lines for unequal hours, 1-12, by single hours. The reverse of the tympan is plain, but shows construction marks. In particular one sees raised dots from the centers of the altitude circles on the front. There exists a raised pin to hold the tympan in place in the mater. A second pin is missing.
Function: An astrolabe is an astronomical instrument used to find the time, do surveying, and make astronomical calculations.
Historical Attributes: Astrolabes from the Paris workshop of Jean Fusoris, circa 1400, typically contain four or five brass tympans with projections for four to eight European latitudes within the range of 40° to 56°. This example at Harvard, however, has a single, silver tympan inscribed for 34°, the latitude of Fez and Rabat (Morocco), Sultanabad (Iran), Herat (Afghanistan), and within half a degree of Damascus and Baghdad. This astrolabe was made for a client who needed a low-latitude instrument for use in the Islamic / Arabic world.
Curatorial Remarks: XRF analysis of the metals was done by Katherine Eremin and Sara Schechner in August 2007.
Related Works: Emmanuel Poulle, Un constructeur d'instruments astronomiques au XVe siècle, Jean Fusoris (Paris, 1963).
Published References: Sara Schechner, "Astrolabes and Medieval Travel," (forthcoming in Ashgate volume, 2008).
Eva Koleva Timothy, Lost in Learning: The Art of Discovery (Newburyport, MA: Athenaeum Publishing, 2010).