Al-Zarqali's universal astrolabe plate

In 11th-century Toledo, Ibrahim ibn Yahya al-Zarqali developed an astronomical plate that did not require a replacement horizon plate whenever the observer changed latitude; it became known as the zarqaliyya and, in European usage, the saphaea ¹. This was an improvement within the astrolabe tradition, not invention of the astrolabe from nothing or proof that every later universal instrument descended from it ³. Universal means applicable across latitudes, not a machine that discovers location and time without knowledge or interpretation ². The photograph shows a display copy in Cordoba, not an object authenticated as al-Zarqali's own work ⁴.

The plate is a geometrical representation of the sky on a disc, with lines for moving between coordinate systems and a ruler representing the horizon ¹. An ordinary planispheric astrolabe carries a rotating star-and-zodiac network above a plate appropriate to a particular latitude; the zarqaliyya instead combines coordinate grids on its surface, without that rotating network on the front ⁵.

The disc is not a photograph of the sky: it represents angular relationships and circles projected from an imagined sphere onto a plane ⁶. Coordinates are different addresses for the same position, expressed relative to the celestial equator, the ecliptic or the observer's horizon ⁷. The instrument organizes these relationships for calculation, but a person still chooses the inputs and reads the marks ².

The difficulty was not absence of earlier astronomical instruments: an ordinary astrolabe's horizon was drawn on a plate associated with a particular latitude ⁸. Moving north or south changes the horizon's relationship to the celestial sphere, requiring a suitable plate ⁶. The universal plate addresses a design question: could a different representation allow one disc to serve multiple latitudes? ²

The zarqaliyya remains part of astrolabe construction and spherical geometry; the study compares the projections by their viewpoints and coordinate representation ⁹. Its story does not begin with a sky previously beyond calculation, nor erase earlier work because a new solution relaxed one instrument's constraint ¹⁰.

Roser Puig describes al-Zarqali as a Toledan instrument maker who taught himself astronomy and worked with Said al-Andalusi under the city's ruler al-Mamun ¹. This was the 11th-century ruler of Toledo, not the Abbasid caliph who lived centuries earlier ¹. Bir and colleagues connect his prominence with precision craftsmanship and participation in observation ¹¹.

Puig reports a 14th-century Egyptian witness to a lost work by Said: al-Zarqali constructed an instrument called al-zarqala for al-Mamun in 1048/1049 and wrote 100 chapters on its use ¹. This is a report transmitted through a later witness, not a foundation document independently read by this museum or a signature dating every plate variant; the record therefore dates the design to the 11th century rather than applying that year indiscriminately ¹. The different treatises also show an instrument accompanied by explanation and teaching, not an isolated disc ¹².

Al-Zarqali is the improver of this particular design and author of treatises about it; Puig distinguishes his observations, tables and other instruments from the universal plate ¹. The equatorium representing planetary circles, for example, is another instrument: its treatment of Mercury must not become an explanation of the plate's mechanism ¹.

The Bibliotheca Alexandrina Antiquities Museum explicitly names him in its section on Muslim astronomers: a cited biographical classification, not an inference from name or country ¹³. The browser's Sunni default is a declared presentation rule, not a quotation asserting that he personally professed a particular legal school; neither the institutional account nor Puig's biography supplies such a personal declaration ^{13 1}.

The change begins with projection: Puig describes replacing the standard astrolabe's equatorial stereographic projection with a meridian projection onto the solstitial-colure plane, viewing from the equinox points and combining the representations ¹. Put simply, a different geometrical arrangement maps the celestial sphere to the disc; the sky itself has not changed ⁹.

The front combines equatorial and ecliptic grids: the first represents right ascension and declination, the second longitude and latitude relative to the ecliptic ⁷. A horizon ruler allows representation of the third system, altitude and azimuth associated with the observer's location ¹⁴. Lines and marks thus support conversion between celestial addresses without engraving a separate horizon plate for each latitude ⁶.

The study explains that circles on the sphere become circles or straight lines in this projection and that angles are preserved, making the drawing useful for calculation ¹⁵. Reading precision is not unlimited: its construction discussion recommends a size that makes marks distinguishable, with different graduation marks for different intervals ¹⁶. Fine engraving does not mean all surviving instruments have identical dimensions ¹⁷.

Puig distinguishes functions on the back, including a trigonometric quadrant and a circle associated with the Moon's distance; Bir and colleagues discuss altitude, calendar, zodiac and sine scales there ^{1 18}. Without examining the photographed copy, every visible curve should not be assigned a specific function: photographs show particular objects, whereas treatises describe designs that can differ ^{4 1}.

The evidence here concerns circulation of texts and knowledge, not sales: Puig identifies a Castilian translation of the zarqaliyya treatise and Latin and Hebrew translations of the shakkaziyya treatise ¹. Bir and colleagues describe its presence in Marrakushi's work on timekeeping, with construction and operating guides in separate sections ¹⁹. This article relies on scholarly identification of those translations, not independent readings of their manuscripts ¹.

That distinction prevents drawing one European route for everything: transmission of a zarqaliyya book is not automatically transmission of identical shakkaziyya details or every other “universal” instrument ¹. The pages read do not count workshops and users or date acquisition by every port ²⁰.

The technical comparison starts with the planispheric astrolabe, its local horizon plate and rotating star network, alongside knowledge of projections and spherical relationships ²¹. The improvement retains the astronomical problem while rearranging coordinate representation and the ruler so that a single latitude no longer constrains the plate ². This is an explainable design relationship, not identification of one physical prototype al-Zarqali copied ²².

The record does not list every earlier astrolabe inventor: the technical pages read do not establish an uninterrupted chain of workshops with every link identifiable ²³. The particular contribution remains clear without suppressing the older instrument's history ².

Puig presents the shakkaziyya as a simplified form in Marrakushi's account, reducing parts of the ecliptic grid and differing from the more elaborate zarqaliyya on the back ¹. This distinguishes named variants in that reference, rather than declaring every later universal astrolabe a direct descendant of one object ¹.

Further evidence includes preservation of Marrakushi's construction account and its modern study and drawing, the subject of the 2020 article ²⁴. These witnesses do not authorize an undocumented family tree extending to every modern navigation instrument ²³.

The identifiable practical change is reduced need for different horizon plates when observing latitude changes; it matters to someone moving a calculation between locations ²⁵. It does not remove the need for coordinate information, a ruler and scale reading: the device organizes relationships for a human user ².

The study connects these instruments with calculation of time and place rather than metal ornament alone ²⁶. The sources read do not establish money or minutes saved, or numbers of sailors carrying one; a design advantage cannot be turned into unsupported statistics ²⁰.

The plate brings craft, geometry and explanation together: sources preserve long treatises, translations and a later construction account, not only a remembered name ^{1 27}. These document teachable knowledge moving between languages and scholarly settings, a narrower claim than one instrument creating all European navigation ¹.

The comparison also shows improvement through representing a known problem differently: celestial angles remain the subject, but their arrangement on a portable readable surface changes ²⁸. This describes a documented technical advance, not civilizational superiority or erasure of translators and copyists ¹.

The claim is specific: Puig and Bir's team attribute the zarqaliyya and treatises to al-Zarqali and explain the departure from ordinary astrolabes ^{1 29}. The browser therefore records an improver, not inventor of every astrolabe or every latitude-independent solution ².

Four dates must remain distinct: design, composition of a treatise, copying a manuscript and manufacture of a surviving object; one does not automatically date the others ^{1 30}. Nor does the 2012 photograph date manufacture of its display copy or authenticate it as the Andalusian original ³¹. The design attribution can remain documented while those limits stay visible ¹.

Louvre Abu Dhabi lists a brass saphea, LAD2019.001, ca. 1224, diameter 28.3cm, possibly produced in Andalusia, and described as on display when consulted ³⁰. That catalogue does not establish that al-Zarqali made it or that its manufacture dates the invention ³⁰.

The photograph selected here shows a display copy at Torre de la Calahorra in Cordoba according to its photographer's description; the museum has not adopted that description's claim about an original elsewhere as an up-to-date provenance record ⁴. An idea can be encountered in a metal exhibit and studied in a book without equating a teaching copy with a historical original ^{4 32}.

Textual witnesses include the treatises and translations Puig distinguishes and Marrakushi's account discussed in the modern study; the original manuscripts were not independently examined for this record ^{1 33}. Note 34 on p. 52 of the study identifies an instrument in the Bibliotheque nationale de France used for one drawing, but publication does not automatically license its modern photograph ³⁴.

The Louvre object and licensed Cordoba-copy photograph are different witnesses, not authenticated views of the same object ^{30 4}. Keeping them separate prevents an attractive image from standing in for missing ownership or dating evidence ⁴.

European names retain traces of transmission: Puig discusses variants of al-Zarqali's name and the plate treatises, while the photograph's caption calls the copy an Azafea ^{1 4}. A name is a linguistic and scientific trace, not sufficient evidence for dating each object bearing it ¹. The sources used do not document a particular film or novel featuring this plate, so none is invented here ³⁵.

Imagine a sky map whose horizon changes as you travel north or south; an ordinary plate suits a particular latitude ⁶. Instead of carrying a plate for every location, al-Zarqali used grids and rulers adjustable across latitudes ¹. Universal does not mean it knows your location by itself: a person still reads and calculates, while the lines connect different ways of describing the sky ².

• Roser Puig, al-Zarqali biography, pp. 1258–1260: instruments, treatises and translations.
• Bir, Bütün, Kaçar and Akın, zarqaliyya guide, pp. 40–41,46–54; the rest of the study was not read in full for this record.
• Bibliotheca Alexandrina Antiquities Museum, named Muslim-astronomers section: biographical classification.
• Louvre Abu Dhabi, LAD2019.001, object fields.
• Codex photograph and metadata, display copy; CC BY-SA 3.0.