History of Science Museum: Collection Database Search


Inventory no. 52869 - Former Display Label

The Saphæa Arzachelis

The universal astrolabe projection developed by az-Zarqellu in Toledo in the 11th century (see the label 'The az-Zarqellu Projection' in the vertical bay displaying maghribî astrolabes) was known in medieval Christian Europe as saphæa arzachelis. This projection, described in 13th century translations, from different Arabic originals, both in the Libros del saber (c.1277) of Alfonso el Sabio of Castile and by Prophatius Judæus in 1263, appears later to have been forgotten, or little used, until its reintroduction in the 16th century by Gemma Frisius who called it the astrolabum catholicum (see the label 'The Astrolabum Catholicum of Gemma Frisius' in one of the horizontal cases to the left).

The mater (lower right) of the late Gothic astrolabe of ?c. 1400 shown here is one of the very few examples of this projection on a non-Islamic astrolabe before its reintroduction by Gemma Frisius. Another example occurs on an astrolabe of 1486 by Hans Dorn, now in the Muzeum Universytetu Jagiellonskiego, Cracow, Poland.

The astrolabe is neither signed nor dated and its origins are unknown. Brass.

Rete for twenty-three stars, all named: the star-pointers are of the 'wavy flame' type, three with flat rectangular bases, the remainder spring directly from the tracery. The rete appears to be of late Gothic type, most of the tracery consisting of a pattern of straight lines and circles; the section of the equinoctial band, however, is supported by two semi-quatrefoils, and what, in an earlier rete might have been a quatrefoil within the ecliptic circle, has been reduced to a small circle. An unusual feature is that the outer edge of the Capricorn band is cut with 120 teeth, and divided equally into twelve parts named with the months of the year. The position of the vernal point is difficult to determine but appears to be about 12 March. The month 'May' is written "madi" (i.e. madius), a form commonly found in medieval manuscripts from Spain and Portugal.

Two plates, for latitudes: 42°, 45°; 48°, 51°. On each of the plates the circle representing the Tropic of Capricorn is divided into 360° numbered clockwise from the meridian line. Apart from this very unusual feature, the plates are of the usual type with almucantars, azimuths, tropical and equinoctial circles, lines of unequal hours, and the line of twilight.

On the back are a shadow-square, an unequal hour diagram, a zodiac/calendar scale (0° Aries = 111/2 March; eccentric type) and the usual scale of degrees.

Certain features suggest that the back of this astrolabe was engraved, or partially re-engraved, at a later date than the construction of the rest of the instrument: the month 'May' is written "MAIVS" on the zodiac/calendar scale on the back, and not "madi" as on the rete; and the lettering on the back is Roman, whereas on the rete and the saphæa it is Lombardic.

The alidade, horse and pin, and the rule for use with the saphæa, are missing.

Billmeir Collection

Other narratives:

Related Objects: