A remarkable astrolabe mater made by the leading astrolabist of medieval Morocco, Abû Bakr ibn Yûsuf, dedicated to an Almohad prince, Abû Muhammad ‘Abd al-Haqq, in Marrakesh, in the year 603 Hijra [A.D. 1206/07]

International Instrument Checklist number: #4401.

This is a previously undocumented composite astrolabe of exceptional historical interest.

[On astrolabes as historical sources see King, Synchrony, II, pp. 339-402.]

Firstly, the mater was made by Abû Bakr ibn Yûsuf, the leading instrument-maker of the medieval Maghrib. He is known by at least seven other pieces dated between 584 Hijra [= 1188/89] and 615 Hijra [= 1218/19] [see Mayer, Islamic Astrolabists, pp. 32-33; King, “Astronomy in Morocco”, p. 48; section 6.1.1 of the website “Medieval Instruments”; and also the table below]. A description of one of these is conveniently available in Gunther, Astrolabes, I, pp. 263-267 (based on Sarrus).

Secondly, the original astrolabe was made for Abû Muhammad ‘Abd al-Haqq, a sayyid or nobleman, son of one of the rulers of the Almohad dynasty, who called themselves khalîfa, “ruler by succession”, and amîr al-mu’minîn, “prince of the believers”. [On the Almohads see the article “al-Muwahhidûn” by Maya Shatzmiller.] Little is known about this sayyid, least of all his scientific interests. By coincidence, the founder of the Merinid dynasty, who succeeded the Almohads in Morocco, had the same name.

the mater

The distinctive throne with a design à jour resembling a pair of praying mantises facing each other is typical of all of the maker’s works. The suspensory apparatus appears to be original.  The limbus is divided and labelled for each 5° with subdivisions for each 1°.  Inside the mater, there are astrolabic markings for latitude 90° (li-’ard sâd), that is, the North Pole. These would serve didactic purposes. [See King, Synchrony, II, pp. 940-944.] The quality of the engraving enables us to designate the plates as replacements. See further below.

A remarkable amount of information has been engraved on the back of this small instrument. On the outer rim there is an altitude scale on the outside of each quadrant, divided and labelled for each 5° and subdivided for each 1°. The 5°-divisions on the upper left are incised with a groove. Within these is a circular solar longitude scale, with labelled divisions for each 5° of each zodiacal sign subdivided into each 1°. Within this is a concentric calendar scale with labelled divisions for each day of each month of the Julian calendar. The names of the zodiacal signs and Julian months are standard. The innermost scales are divided into 28 labelled parts, for the years of a 28-year solar cycle, starting counter-clockwise from the top, and the corresponding feria or first day of the year (1 for Sunday, etc.). The leap years (2, 6, 10, 14, 18, 22, 26) labelled with the letter kâf, the first letter of the word kabîsa, for “leap (year)”. The order is as follows, with the leap years underlined: 3 4 6 7 1 2 4 5 6 7 2 3 4 5. [On astronomical calendars see the article “Ta’rîkh, 3.1-2” by F. C. De Blois and Benno van Dalen in EI₂.]

Within these scales below the horizontal diameter is a double shadow square for base 12. Only the horizontal (cotangent) scale is visible now, the vertical (tangent) scales have been worn away. The horizontal scale, labelled al-zill a-mabsût, “the horizontal shadow”, is divided and labelled for each 2 units, subdivided for each 1 unit. The arguments for the vertical scale, labelled al-zill al-mankûs, “the vertical shadow”, are visible, although the scale is not. [On the origin of such scales see King, Synchrony, II, pp. 247-252.]

Dedication in Arabic:

sana’ahu li-l-sayyid al-ajall Abû [sic for Abî] Muhammad ‘Abd al-Haqq ibn al-khalîfa amîr al-mu’minîn ibn amîr al-mu’minîn Abû Bakr ibn Yûsuf bi-madînat Marrâkush sanat khâ’-jîm

“Made for the most excellent sayyid, Abû Muhammad ‘Abd al-Haqq, son of the Caliph, (the latter being) the Commander of the Faithful, son of the Commander of the Faithful, by Abû Bakr ibn Yûsuf in the city of Marrakesh – may God make her prosper – in the year 603 (Hijra) [= 1206/07].”

The 3 of 603, or rather the jîm of khâ’-jîm, seems secure, its “tail” being extended to an entire quadrant of a circle, to be symmetrical to the extended word sana on the opposite side of the inscription. The dot under the jîm confirms that this is a “3” not an “8”.

The hole at the centre of the mater is uniformly lined at the centre with silver, an unusual feature. See further below.  The alidade is original and bears markings for the seasonal hours on a universal sundial. [On these see King, Synchrony, II, pp. 253-255.] There is also a sexagesimal scale divided for each 6 units and a set of circular arcs whose function is obscure. The pin is original, the “horse” probably not.

The following list surveys the known instruments of Abû Bakr ibn Yûsuf:

Location. The following abbreviations are used: PLU = present location unknown; London SM = Science Museum; Madrid IVDJ = Instituto de Valencia de Don Juan; Paris BL = collection of Baron Larrey; Rabat KO = Kasba Ouadai; Strasbourg OBS = Observatoire; Toulouse MPD = Musée Paul Dupuy.
Type. A - astrolabe (with M, P and R), M - mater, P - plates, R - rete, UA - universal astrolabe.
International Instrument Checklist number. Series started by R. Gunther in 1932 continued by Derek Price et al., and most recently by David King.
Date is given here in the Hijra calendar. Diameter is given in centimeters. Publication of an instrument means photographic images with detailed descriptions and commentary.

Location                                     type              IIC no.             date            diam.          published

1.           lost                                UA               #4039             584 H              ?                   no

2.           Sotheby’s 2007             M                #4401             603 H            10.2               yes

3.           Strasbourg OBS            A                 #124              605 H            16.5               yes

4.           Rabat KO                        A                #2709             610 H              ?                   no

5.           Toulouse MPD                A                #1090             613 H            13.4               yes

6.           PLU                                  A                 #125              615 H          ca. 70               no

7.           London SM                    RP               #1057                -                     -              yes

8.           Madrid IVDJ                   A                #1069                -                17.6              yes*

Notes:

1. This is known only by a reference in a manuscript datable ca. 1500: see King, Cairo Scientific Manuscripts, pl. LXV on p. 285, and the caption on p. 209, and also no. C26/4.6.4 on pp. 60-61 for the manuscript.

3. Published in Sarrus, “Astrolabe marocain”, and again in Debauvais & Befort, Astrolabes de Strasbourg, pp. 59-121, with superb images. See also Gunther, Astrolabes, I, pp. 263-267.

4. Rete modified by Abu l-Qâsim ibn Ridwân in 776 Hijra [= 1374/75].

5. Published in D’Hollander, Astrolabes de Toulouse, pp. 47-76, with unreliable text and poor images.

6. See Gunther, Astrolabes, I, pp. 267-268.

7. Identified during research for Frankfurt catalogue.

8. Identified during research for Frankfurt catalogue. Catalogued in García Franco, Astrolabios in España, pp. 273-278 (no. 18), without any association with Abû Bakr.

The replacement parts:

The plates and the rete are replacements and they fit perfectly into the mater. Some curious features should be mentioned here. There is a silver lining to the hole at the centre of the mater and rete, and what looks like a brass lining on the holes of the plates and the alidade. No reason for these unusual, and carefully executed, features is apparent; it seems unlikely that the ensemble was thus modified to fit around an existing pin.

The plates are engraved in a later, less elegant Maghribî hand, and therefore seem not to be original. Three were made by the same maker, the fourth by yet another hand.

Three of the replacement plates are engraved with the three base circles for the equinoxes and solstices, as well as for altitudes for each 6° and azimuths for each 10° and the seasonal hours below the horizon. There are special fish-bone markings for evening and morning twilight at 18° below the horizon (labelled shafaq and fajr), and for midday (zawâl), the prayer after midday (al-zuhr) and at mid-afternoon (al-’asr). The prime vertical and also the altitude circle for 18° above the horizon are similarly accentuated (the latter can be used for twilight determinations). [On the definitions of the times of prayer in Islam and the markings for the prayer-times on instruments, see the article “Mîkât” (= astronomical timekeeping) in EI₂, and King, Synchrony, II, pp. 47-50.]

The latitudes served by these three plates are as follows:

21°40¢ — 25° — 30° — 33° — 36° — 36°40¢

Each of these latitudes can tell us something. [See King, Synchrony, II, pp. 921-962.]  We can, for example, be sure that the markings for 21°40¢ were intended for Mecca, since this was a common value for the centre of the Islamic world. Those for 25° would have been intended for Medina. Likewise, we can be sure that the value 36°40¢ was intended for Tunis. For the other latitudes we can only speculate, using the latitudes and geographical information that are found on other Maghribî astrolabes. The value 30° was probably intended for Marrakesh, although Abû Bakr ibn Yûsuf used the better value 31°. The value 33° was probably intended for Fez, although Abû Bakr earlier used the better value 33°40¢. The value 36° may have been intended for Ceuta, although Abû Bakr used the better value 35°20¢.

The fifth replacement plate, probably later than the others, has a hue different from that of the four others, reddish and coppery in places. One side provides astrolabic markings for latitude 0°, that is, the Equator, in the same hand. These again would be for didactic purposes.

On the other side of this plate we find a set of highly ingenious universal markings of the kind first devised by Abû ‘Alî Ibn Bâso in Granada in the early 14^th century. These are unlabelled, confirming a later addition. If they were original to Abû Bakr’s astrolabe, they would overturn all that we know about the originality of Ibn Bâso, which is extremely well documented. [See King, Synchrony, II, pp. 60 and 63, and the three publications of Emilia Calvo in the bibliography.]

The replacement rete is quite different in style and execution from the retes of Abû Bakr ibn Yûsuf, which are far more ornate. [See, for example, Gunther, Astrolabes, I, p. 264.] It is in the style of the simplest Maghribi retes, with both the horizontal bar and the lower equinoctial bar counter-changed, the latter resting on a distinctive circular frame also found on some Andalusî astrolabes. There are some 7+8+7+7 = 29 star-pointers in the four quadrants reckoned counter-clockwise from the vernal equinox on the left. Not all of these are named, and only a few of those that are named are discernible (for example, qalb al-asad, al-a‘zal and al-râmih). The ecliptic is divided for each 5° of each sign and the names of the signs are barely legible. The engraving is in a Maghribî naskhî (note the lâm on al-a‘zal). The rete shows signs of wear, if not excessive use, and the pointer for al-râmih is broken, as is the small rectangular frame at the top of the ecliptic (to mark the winter solstice).