Astrolabe Quadrant

An instrument of Greek origin, the astrolabe[2] was adopted and developed from the eighth century by Muslim astronomers who carried out extensive research in the field of astronomy, notably via the translation of Indian, Persian and Greek scientific works, such as Ptolemy’s Almagest.

The astrolabe quadrant is a variant on the planispheric astrolabe, reduced to a quarter of a circle via the double folding of the stereographic projection, and with no rete[3]. Its function is identical – that of a mobile astronomical measuring instrument. It simulates the movement of the celestial sphere in relation to the referential terrestrial sphere, in order to solve problems of spherical astronomy by combining geometry and trigonometry. It enables the measurement of altitude, latitudes and longitudes, the direction of Mecca, and the time of day and night. Although easy and rather inexpensive to make, the astrolabe quadrant is, however, complicated to use. Each instrument is only valid for one, single latitude. Astrolabe quadrants were used in the Muslim world until the beginning of the twentieth century. We know of examples from the Maghreb in the eighteenth century and from the Ottoman Balkans. [4]

An inscription on the centre of the instrument would seem to indicate the commissioner’s name and a date of manufacture, corresponding to the eleventh month of the year 1038. Unlike the majority of Maghrebin and European astrolabe quadrants from the medieval period, made from engraved brass, this instrument was made from a parchment-covered wood core, materials out of which a number of later Ottoman astrolabes were made. [5] If we consider, in addition, that the first preserved astrolabe quadrants only date back to the twelfth century, and that the first written accounts of the instrument date back to the thirteenth century, it is likely that this object is a historical fake and that the date written on the obverse does not correspond to the date the object was actually made.

In general, astrolabes are rarely decorated. However, the material this one is made from meant its maker could decorate the instrument with motifs often seen on ceramics, stucco and of course, paper – a frieze of foliage scrolls and forked palm leaves, done in black ink.

These motifs are similar in style to certain decorations found on pieces produced in Ayyubid Syria (1169-1260), such as on the Louvre Museum’s bowl with vegetal decoration[6].

The instrument’s graduations are set back from the ornamental strip, on an area void of  decoration, and made of three marked strips. The first indicates 90°, the second is graded in increments of 10°, and the last one in increments of 15°. In order to determine the different graduations, the inside of the instrument is equipped with several spokes in black ink, which have partially disappeared.

This instrument bears witness to the numerous passages between the two shores of the Mediterranean that operated via Spain. Al-Andalus experienced major cultural expansion, enriched in particular by the presence of Jewish scholars, and its geographical proximity to the Christian world. The writings of Prophatius Judaeus[7], a famous Jewish astronomer and mathematician born in Marseille, bear witness to this. He appears to be the first to describe the astrolabe quadrant, which he called: roba‘ Yisrael or quadrans novus in order to distinguish it from previous quadrants. His writings were mentioned by Dante Alighieri[8] in his Divine Comedy. For a long time, Prophatius’ account led people to believe, wrongly, that the instrument in fact originated in medieval Europe, and that it was handed down to the Arab world, where the first preserved treatise describing its use dates back to the fourteenth century[9], shortly after Prophatius’ treatise.

[1] Emir of the Maghraoua (Berber tribe) who governed Fes at the time.

[2] The terms comes from the Greek astron and labê meaning “which takes the stars”.

[3] The rete (or spider) is a component of the astrolabe, made from an open-work, reticulated plate, which is rotated around a pivot using a handle. It represents the sky of the fixed stars, which rotates around the tympanum, representing the immobile earth.

[4] Quadrant signed Muhammad ibn ‘Alî Mursîl al-Andalûsî, Morocco (Wazzân), Eighteenth century, M.A/A.O,  n°MN.AM 1963.6.2 ½.

[5] Late quadrant, made in Turkey around 1820, Paris, Institut du monde arabe, Al 04-07.

[6] Bowl MAO 112, painted in blue and black, under transparent colourless glaze, made in Syria in the late twelfth or early thirteenth centuries.

[7] Jacob ibn Machir ibn Tibbon, 1236-1312.

[8] Florentine poet, writer and politician (1265-1321).

[9] The flowering gardens on the use of the astrolabe quadrant (al-Rawdât al-muzhira fî al-‘amal bi-rub‘ al-muqantarât), by Ahmad al-Mizzî in 1349.