A silver astrolabe with Sanskrit inscriptions and a single plate calibrated for the latitude 26 degrees north, Jaipur, India, 19th century

formerly in the collection of the Time Museum, Rockford, Ill. (inventory no. 1752)

Turner, A. J., The Time Museum, Catalogue of Collection, Vol. I, Part 1: Astrolabes, Astrolabe-related Instruments, Rockford 1985, pp. 118-119, figs. 98-99

in good condition, minor pitting and patination and surface scratches, as viewed
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Sawai Jai Singh (1688-1743), ruler of Jaipur, had a great esteem for the astrolabe, although he preferred, for astronomical observations, huge masonry instruments which he erected in his five observatories in northern India.  Besides commissioning a Sanskrit translation of Nasir al-Din al-Tusi's popular Persian work on this instrument, he himself composed a manual in Sanskrit. He also appears to have established a workshop for producing Sanskrit astrolabes, mainly with a single plate calibrated for 27° N, which is the latitude of Jaipur. He seems to have realised, quite rightly, that the best way to popularise the astrolabe was to divest it of unnecessary peripherals and make it simpler. There survive scores of such single plate Sanskrit astrolabes in various collections. These were produced throughout the nineteenth century, in Jaipur and Kuchaman both in Rajasthan and situated on 27º N latitude and in other places in northern India. The last known Sanskrit astrolabe was produced by one Haridatta of Kuchaman as late as 1903.  

Seeing the great demand for these astrolabes, some enterprising jewellers (probably of Jaipur) began to produce silver astrolabes in the late nineteenth century. Three are known. One each of two identical specimens with a diameter of 21.2 cm is now in the Science Museum, London (# 1990-65), and in the National Museum, New Delhi (Acc. No. 86.193/1). The present astrolabe is the third extant silver astrolabe, and differs from the other two. It was formerly in the collection of the Time Museum, Rockford, Ill. (inventory no. 1752) and was described by A. J. Turner (pp. 118-119, figs. 98-99).

This large astrolabe consists of a single plate calibrated for the terrestrial latitude of 26º (roughly corresponding to Jodhpur, Rajasthan).  It is surmounted by a high lobed and scalloped kursi (throne).  The body and throne are made as one piece from the same sheet of silver. The astrolabe is suspended by a shackle and a large ring. 

On the front of the plate, the limb is graduated for each degree of arc, and into groups of 6º.  These groups are numbered separately for each quadrant from 1 to 15.  The numbering starts from the east and west points respectively and reaches up to the south and north points.

On the plate are drawn south-north and east-west lines, and the concentric circles to represent the tropic of Capricorn, the celestial equator, and the tropic of Cancer.  Altitude circles are drawn for each 2º, and azimuths for each 4º above the horizon and for each 2º below the horizon. Lines for unequal hours are drawn as continuous arcs from the centre.  However, none of these three sets of lines are labelled.  The plate is calibrated for the terrestrial latitude 26º N but there is no label displaying this value. 

The rete has a remarkable similarity with the rete in a large (30.4 cm diameter) and heavy 6-plate Sanskrit astrolabe now in a private collection in France. There are slight differences in the placement of star pointers; some look like mirror images (that is, laterally inverted) of those in the 6-plate astrolabe.  Obviously the maker of this silver astrolabe had either this astrolabe or one similar to this as his model

On the rete, there are circles representing the tropic of Capricorn, the equator and the ecliptic. These circles are held together by the east-west bar, which is counter-changed at the centre and in the west, but not in the east.  The circles of Capricorn and the equator are held together in the lower half by three X-shaped trusses.  In the middle of the truss to the left, there is a handle to rotate the rete around the centre.  The ecliptic circle is divided into the 12 signs of the zodiac and labelled accordingly: mesa (Arius), vrsa (Taurus), mithuna (Gemini), karka (Cancer), simha (Leo), kanya (Virgo), tula (Libra), vrscika (Scorpio), dhana (sic read dhanus, Sagittarius), makara (Capricorn), kumbha (Aquarius), mina (Piscis). Each sign is further subdivided into five parts of 6º each and numbered as 6, 12, 18, 24, 30 in the clockwise direction. The bevelled edge of the ecliptic circle is graduated in single degrees.

Leaf-shaped star pointers arise out of the circles representing the tropic of Capricorn, the equator, the ecliptic, the east-west bar, and the large circle at the centre.  These pointers serve the following 25 stars, reading counter-clockwise in each of the four quadrants (9+4+6+6) from the vernal equinox on the left hand side:

Samudrapaksi (iota Ceti)  -  Simha-hrdaya  (alpha Leo.) (sic see below) -  Asvini (gamma Ari.) - Bharani (41 Ari.) - Manusyapaksi  (sic read Manusyaparsva) (alpha Pers.) -  Rohini  S (alpha Taur.) -  Mi[thuna]va[ma]pa[da]  (gamma Ori.) -  Vrahmahrdaya (sic read Braº) (alpha Aur.) - Ardra (alpha Ori.) //   Lubdhaka (alpha Can. Mai.) - Mi[thuna-daksina]pada] (beta Ori.) -  Lubdha[ka]bamdhu (alpha Can. Min.) -  Mahapurusa (alpha Hydr.) // Hasta (delta Corv.) -  Ja.pha (sic U[ttara]pha[lguni] (beta Leo.) - Citra (alpha Virg.) - Marici (beta Urs. Mai.) -  Svati (sic Svati) (Boot.) -  Sarghothiva (sic Sarpagrva) (alpha Serp.) // Abhijit (alpha Lyr.) -  Sravana (Aqil.) -  Kurkatapucha (sic Kukkutapuccha)  (Cygn.) -  Asvamukha N (epsilon Peg.) -  Satabhisa  (lamda Aquar.) -  Purvabhadrapata (sic ºpada) (beta Peg.). 

Besides these 25 star names, 4 more are engraved on the rete without the corresponding pointers. Thus on the east-west bar, Madhvodara (sic Matsyodara) (beta Andr.); on the ecliptic,   Krti (sic Krttika) (eta Tau.) -  Ci.pu.pu.ta. (sic Punarvasu) (beta Gem.) -  Pu[rva]pha[lguni] (delta Leo.) -  Visakha  (iota Libr.) -  Anuradha  (delta Scorp.).  The engraver erroneously interchanged the positions of  Matsyodara (beta Andr.) and Simha-hrdaya  (alpha Leo.) which should occupy the eastern and western parts of the east-west bar.

On the back of the plate, the rim is graduated for each degree of arc.  In the upper half, the rim is further divided into groups of 6º, which are labelled separately for each quadrant as 6, 12, 18 ... 78, 84, 90, starting respectively from the east and west points and reaching the south point. The vertical and horizontal diameters divide the back into four quadrants. In the upper left, there is a trigonometric quadrant with an orthogonal grid for each unit of the radii up to 30. The upper right is occupied by a solar quadrant with axial scales and associated quarter circles for each 6º of solar longitude, labelled from the winter solstice to the summer solstice on the vertical axis (makara, kumbha, mina, mesa, vrsa, mithuna) and from the summer solstice to the winter solstice on the horizontal axis (karka, simha, kanya, tula, vrscika, dhanu).  The two lower quadrants are occupied by shadow squares, the left by the square for a gnomon of 12 inches, and the right for a gnomon of 7 inches. The sides of the squares are divided respectively into 12 or 7 units and numbered accordingly; these units are further sub-divided into 6 parts each. The squares are labelled on the left along the vertical side as dvadasamgula-vilomachaya ("reverse shadow of a 12-inch [gnomon]), along the horizontal side as dvadasamgula-samachaya ("direct shadow of a 12-inch [gnomon]); on the right, along the horizontal side as satpamgula-samachaya (sic saptaº) ("direct shadow of a 7-inch [gnomon]), and along the vertical side as satpamgula-vilomachaya ("reverse shadow of a 7-inch [gnomon]).

An alidade is pivoted to the centre at the back. Its right and left halves are divided into 30 parts each and numbered accordingly from the centre.  The maker failed to add sights to the alidade; consequently it is non-functional. A pin and wedge hold the parts together.

The astrolabe is neatly made, the geometrical lines are drawn accurately, and the legends and numbers are engraved almost correctly. The numerals bear close resemblance to modern printed characters. 

Bibliography: Turner, A. J., The Time Museum, Catalogue of Collection, Vol. I, Part 1: Astrolabes, Astrolabe-related Instruments, Rockford 1985