Astrolabe of 'Umar ibn Yusuf ibn 'Umar ibn 'Ali ibn Rasul al-Muzaffari

A brass astrolabe signed and dated 690 AH / 1291 CE by its maker, a Rasulid prince of Yemen who three or four years later briefly ruled the kingdom as Sultan al-Ashraf 'Umar II. It is one of the small number of medieval Islamic scientific instruments whose maker also left behind his own written manual on how to build it, complete with notes from two teachers certifying his skill. The astrolabe's rete carries an unusual scale for the lunar mansions, and its plates are engraved for the latitudes of Yemen and the Hejaz using the tables set out in that same manual rather than by direct geometrical construction.

Nothing is recorded of the object between its making in 1291 and its appearance, roughly six centuries later, in the New York collection of the Tiffany silversmith and pioneer collector of Islamic art Edward C. Moore, who bequeathed it to the Metropolitan Museum in 1891. It has been in the Museum's Department of Islamic Art ever since.

What it is

An astrolabe is a hand-held computing instrument, a brass disc-based model of the sky that lets its user solve a fixed set of astronomical problems by turning one part against another rather than by calculation. This example survives as a complete assembled set: a case 15.6 cm across, a pierced rotating net (the rete, carrying pointers to fixed stars and set within the rim of the case), four interchangeable plates engraved for different latitudes, a sighting bar (the alidade) with its retaining pin, and the central pin and wedge that hold the stack together so the whole instrument can be turned in the hand.

It is a brass object, cast and hammered into shape, then pierced, chased and inlaid with silver for its lettering and scale markings. That combination of casting, piercework and silver inlay is standard for the finer astronomical instruments of the medieval Islamic world, and distinguishes an object made for genuine use and display from a cruder working tool.

How the plates and rete were built

The four plates are engraved for latitudes covering Yemen and the Hejaz, the two regions the maker's own household and travels connected: Yemen where he ruled, and the Hejaz, home to Mecca and Medina, orientation toward which is one of an astrolabe's standard uses. According to the modern academic study of this specific instrument, the plates were not laid out by the direct geometrical projection more usually described in Arabic treatises on astrolabe-making, but were calculated from tables the maker set out in his own separate manual on the subject. That manual gives tables for constructing the altitude circles and azimuth circles for particular Yemeni and Hejazi latitudes, tables of shadow-lengths, and the solar altitude at the start of the afternoon prayer.

The rete carries an additional feature that is not typical of astrolabes from this period: a graduated scale for the twenty-eight lunar mansions (manazil al-qamar), the stations the Moon appears to pass through each month, used across the medieval Islamic world for timekeeping, weather lore and agricultural reckoning quite apart from formal astronomy. The back of the case, in turn, is engraved with astrological information rendered in planetary symbols that had reached Islamic astronomy from Greek sources. The academic literature on this piece describes this back as 'virtually identical' to the illustration of an astrolabe's back given in the maker's own treatise, which is the clearest single piece of evidence tying the surviving object to the surviving text.

That match is not total. The star pointers actually fitted to this rete do not correspond to the star positions the same treatise tabulates. Nobody has resolved why; it stands as an open inconsistency in an otherwise unusually well-documented pairing of instrument and manual.

The prince who signed his own instrument

The maker gives his own name and lineage in the signature: 'Umar ibn Yusuf ibn 'Umar ibn 'Ali ibn Rasul al-Muzaffari. He was born around 1242, a son of al-Muzaffar Yusuf I, the second sultan of the Rasulid dynasty that had ruled Yemen since 1229 and whose own reign, from 1249, ran for close to half a century. Little is recorded of 'Umar's early life. In 1266 or 1267 he commanded a military expedition for his father to the northern town of Hajja, and he later served as governor of al-Mahjam, on the Wadi Surdud in coastal Yemen. His father made him coregent in 1295; four months later, on al-Muzaffar's death, he succeeded to the throne as al-Malik al-Ashraf, Sultan al-Ashraf 'Umar II, the third Rasulid sultan.

His reign lasted about twenty-one months. He died on 22 November 1296 and was buried in the Ashrafiyya school he had founded at Ta'izz. He left six sons and two daughters, the daughters married to sons of his own successor, his younger brother al-Mu'ayyad Da'ud. This astrolabe was made in 1291, several years before any of that: it is the work of a prince, not yet of a sultan.

A reign of twenty-one months, and a longer scientific record

Set against his father's long and, by the standard accounts, prosperous rule, al-Ashraf's own brief reign is described in the modern scholarly literature as of no major political significance. The same scholarship is explicit that this is not the measure by which he is remembered: his importance rests on his scientific output, which was set down independently of, and mostly before, his short time on the throne.

He is credited with some thirteen treatises across medicine, genealogy, agriculture, veterinary medicine, astronomy and astrology, and with building astronomical instruments himself, astrolabes among them. One modern assessment of him, from a scholar who has studied his astronomical writing directly, puts it plainly: he 'was not a great genius but a teachable pupil and a versatile scholar.' That is a considered, unflattering judgment from someone who read the material, not a dynastic compliment, and this record treats it as the more reliable of the two available pictures of the man.

The treatise, and the teachers who certified him

Separately from this astrolabe, 'Umar left a manual on how to build one: a work usually cited as Mu'in (or Minhaj) al-tullab fi al-'amal bi'l-asturlab, on the construction of the astrolabe and other instruments, surviving in two manuscripts, one in Cairo (commonly cited as held in Dar al-Kutub, the Egyptian National Library) and one in Tehran. In it he explains the construction of the astrolabe with diagrams of its parts, gives the tables for Yemeni and Hejazi latitudes described above, and goes on to cover the horizontal sundial, the water clock, and the magnetic compass, in the course of which he wrote what is described as the first description in a medieval astronomical treatise of the magnetic compass, and the first use of it there as a qibla-indicator: a floating compass bowl with an inserted needle, used to find the sacred direction toward Mecca under conditions, such as bad weather, where the sky itself could not be used.

At the end of the treatise, two of his own teachers added notes. They record that they had inspected some four to six astrolabes made by 'Umar himself, found them accurate and skillfully made, and formally certified his competence, giving him leave to make astrolabes as he saw fit; they also mention two water clocks of his. Whether this particular Metropolitan Museum astrolabe is among the instruments the teachers actually inspected is not stated anywhere in the sources consulted for this record, and should not be assumed; the certification is general to his craft, not a description of this specific object. What is specific to this object is the match, described above, between its back and the treatise's own diagram of an astrolabe back. It is rare, in the surviving literature of the medieval Islamic world, to be able to hold in hand both an instrument and the manual its own maker wrote for building it; that pairing, not a claim that the treatise names this exact piece, is the documentary strength this record can support.

What it was for

An astrolabe of this kind served both an astronomical and a devotional function, and the two were not separate in practice. Its plates and rete let a user find the time of day or night from the altitude of the Sun or a known star, and from that derive the times of the five daily prayers, a routine and expected use of the instrument across the medieval Islamic world. Its maker's own separate work on the magnetic compass, described above, addressed the same religious requirement from another angle: establishing the qibla when neither sun nor stars were available to sight by. The astrological information engraved on the back, using planetary symbols carried into Islamic astronomy from Greek sources, points to the instrument's second, non-devotional use, in judicial and natal astrology, a discipline 'Umar treated systematically and at length in his own separate fifty-chapter compendium (see Related works). Nothing in the sources consulted suggests any further private or esoteric use beyond these ordinary, well-documented functions of timekeeping, prayer and astrology as they were practiced at a Rasulid court; this record does not manufacture one.

A dynasty that kept producing scholar-princes

'Umar was not an isolated case inside his own family. The Rasulid sultans of Yemen, who ruled from 1229 to 1454, are recorded across multiple generations as patrons and, more unusually, practitioners of astronomy, medicine, botany, agriculture and veterinary science, and Rasulid-founded schools in Ta'izz and elsewhere taught these subjects alongside jurisprudence and mathematics. Nearly a century after 'Umar, the Rasulid sultan al-Afdal al-Abbas (r. 1363-1377) compiled a six-language comparative dictionary, now known as the Rasulid Hexaglot, and his successor al-Ashraf Isma'il I continued the same pattern of scholarly patronage into the last decades of the fourteenth century. Read against that longer record, 'Umar's astrolabe and its accompanying manual are not a freak survival but one dated, signed data point inside a documented, multi-generational royal habit of doing science rather than merely funding it.

Six centuries of silence, then a Tiffany silversmith's cabinet

Between the astrolabe's completion in 1291 and its next documented appearance, nothing is recorded in the sources consulted for this record. No owner, sale, gift or seizure across roughly six centuries is named anywhere found in the course of this research. That gap is recorded here as a gap.

The instrument surfaces in the historical record again in the collection of Edward C. Moore (1827-1891), the New York silversmith who from the 1860s and 1870s became one of the earliest serious American collectors of Islamic art, assembling it in large part as a working reference library of design and technique for his own studio, which Tiffany and Co. had acquired in 1868 and which he went on to direct as chief designer. On his death in 1891 Moore bequeathed roughly four hundred objects from the Islamic world to the Metropolitan Museum, the Museum's first major group of Islamic material and, at the time, its largest and most comprehensive. This astrolabe was accessioned from that bequest as 91.1.535a-h, alongside other Rasulid metalwork from the same gift, including a brass brazier bearing the name of 'Umar's own father, al-Muzaffar Yusuf I (Metropolitan Museum, accession 91.1.540). Exactly how, when, or from whom Moore acquired the astrolabe is not stated in the sources consulted for this record.

What is still unresolved

The largest gap is the plainest one: where the astrolabe was, and in whose hands, for roughly six hundred years between its making and its documented presence in Edward Moore's New York collection before 1891. Nothing in the sources consulted narrows that gap. A smaller, more technical puzzle sits inside the object itself: the mismatch between the star positions engraved on the rete and those tabulated in the maker's own treatise, on an instrument whose back otherwise matches that same treatise closely enough to be called virtually identical to it. Neither question has an answer in the literature this record was built from, and both are recorded as open rather than guessed at.