The Astronomical Observatories of Jai Singh c7: Chapter IV.—The Zarqālī Astrolabe

The Astronomical Observatories of Jai Singh c7

Language: English

Chapter IV.—The Zarqālī Astrolabe

c7.1

16. The instrument shown in figures 19 and 20 is dated the 23rd year of the reign of Aurangzeb and A. H. 1091 (A.D. 1680), and was made at Delhi for Nawab Iftikhār Khān of Jaunpur¹ by a certain Ziā al-Dīn b. Mullā Qāsim Muḥammad b. Ḥāfiz Īsā b. Allah Dād, Humāyūnī, aṣṭurlāb maker of Lahore.² The instrument is now at Jaipur. It is labelled ‘Yantra Jara Kālī sarva deśī.’ It is two feet in diameter and is made of brass and consists of one disc only engraved on both sides and is described in the inscription as a ‘Zarqālī astrolabe’³ and as a ‘single leaf’ instrument.

c7.2

¹ The reading of this word is uncertain, but Iftikhār Khān was possibly Sulṭān Husain, who in the first year of ‘Alamgir was given the title ‘Iftikhār Khān’ and who was Faujdār of Jaunpur where he died in A. H. 1092 (=A.D. 1681-2).

c7.3

² This appears to be the maker also of the very fine ‘complete’ astrolabe (Jaipur B, figures 6 and 8) made in A.D. 1657).

c7.4

³ Al-Zarqālī called it al-‘Abbādiya in honour of al-Mu‘tamid b. ‘Abbād, king of Seville (A.D. 1068-1091). See C. Nallino. *Encyclopædia of Islām* p. 502.

c7.5

The invention of this instrument is usually attributed to Ibrāhīm b. Yaḥyā al-Naqqāsh (the engraver), born at Cordova, and who lived from about A.D. 1029 to 1087.⁴ He was known as al-Zarqālī (Arzachel) and his instrument was called al-ṣafīḥat al-zarqāliya “the tablet of al-Zarqālī” and was famous in mediaeval Europe under the name Saphaea Arzachelis.

c7.6

⁴ Suter (p. 109), who also records (p. 163) that one Aḥmad b. M. b. ‘Othmān al-Azdī, who died at Morocco about A.D. 1340, also wrote on the use of the Sakārī and Zarqālī Safīḥa. For a brief description of the instrument see also L. A. Sédillot’s *Mémoire*, p. 184 and fig. 95.

c7.7

17. The characteristic part of the instrument is engraved on the reverse. The ordinary astrolabe was considered inconvenient, inasmuch as for every new latitude an additional tablet was required. Al-Zarqālī tried to remove this difficulty by substituting a horizontal projection for the usual polar projection. He took as his centre of projection one of the equinoctial points, and made the solstitial colure (i.e., the great circle passing through the solstitial points and the poles of the equator) the plane of projection.⁵

c7.8

⁵ In figure 25, PP¹, are the poles of the equator, K¹ is a pole of the ecliptic, and Pr. P¹ is the equinoctial colure. The centre of projection is ♁ and pc q p¹ is a half of the projected solstitial colure. In the figure circles of declination, etc., are drawn for angles of 30°, 45°, and 60°. D₁D₁, D₂D₂ and D₃D₃ are circles of declination. pA₁ p¹, pA₂p¹, pA₃p¹ are circles marking right ascension; similarly L₁L₁, L₂L₂, L₃L₃ are circles of latitude, and l₁K₁, l₂k₁, l₃k₁ circles of longitude. On the instrument itself circles of declination and latitude are drawn for every degree, and those for right ascension and longitude for every three degrees. The latitudes and declination circles are numbered from the centre to the poles; the ecliptic is marked with the signs of the zodiac from O to F (figure 21), and back again from F to O, and similarly along the other half of the ecliptic line, and each sign is graduated for every three degrees; the graduations on the equator commence at D and proceed on the north side of the line to B which is numbered 180, and then the graduations are continued on the south side of the line ending up at D, which is this time numbered 360.

c7.9

The projections of the two celestial hemispheres exactly coincide, and the scheme can be used for any geographical latitude. By the aid of the index and sighter most of the results given by the ordinary astrolabe can be obtained. The index of the Jaipur instrument consists of cross bars (four arms at right angles).

c7.10

The projection was used for mapping out both the celestial hemispheres. For example we have (fig. 21) the stars Simāk-Rāmiḥ (Arcturus) and Fam al-Faras (Enif) placed near each other something like this

c7.12

Their right ascensions may therefore be read

c7.13

| F | 52 | or | 308 |
| S | 59 | or | 301 |

c7.14

But, as the scale on the instrument commences at the winter solstice,¹ and the first point of Aries is reckoned as 90 instead of 0 we must deduct 90

c7.15

¹ al-Hasan b. ‘Ali b. ‘Omar al-Marrākoshi, Abū ‘Ali (fl. A.D. 1262) appears to have been the first to employ Right ascensions, which he reckoned from the first point of Capricornus. See E. B. KNOBEL, The Chronology of Star Catalogues, p. 14.

c7.16

| F | -38 | or | 218 |
| S | -31 | or | 211 |

c7.17

According to Flamsteed, F was approximately 322°, which is the same as -38° (360°-322=38) and S was approximately 210½°.

c7.18

In Appendix A4 the names and approximate positions of certain stars on the instrument are compared with the positions as given by Flamsteed.

c7.19

18. There are also the names of several stars written in the Devanāgarī character, e.g., Marīchi with R. A. 204° and declination 51°N., and Pulaha with 19½° or 160½° and 63 N. The former is usually identified with η Ursae Majoris, for which Flamsteed gives R. A. 203° 50' and declination 50°53'; and Pulaha may be α Ursae Majoris, for which Flamsteed gives 161° 2½' and 63° 25'.

c7.20

Also the names of a number of towns are given, i.e., the celestial map is also used for geographical purposes. The axis CA appears to have been taken as zero longitude, and Baghdād, or some place with nearly the same longitude, appears to have been considered as situated on this axis.

c7.21

FIG. 21. STAR MAP OF ZARQALI ASTROLABE.

c7.22

FIG. 22. SINE TABLE OF ZARQALI ASTROLABE.

c7.25

Some of the towns and their positions are given below:—

c7.26

| Name of Town. | Longitude with reference to C A in figure 21. | Latitude with reference to D B in figure 21. | Longitude with reference to Baghdad as given on Jaipur B. | Latitude as given on Jaipur B. |
| | | | ° ' | ° ' |
| Ḥalab (Aleppo) . . | -8 | +35¾ | -7 50 | +35 30 |
| Ṭūs . . . . | +13 | +37 | +12 30 | +37 0 |
| Kābul . . . | +24¼ | +34 | +24 40 | +34 7 |
| Jahānābād (Delhi) . | +34 | +28¼ | +33 35 | +28 39 |
| Lahore . . . | +29¼ | +31¼ | +29 20 | +31 50 |

c7.27

19. The obverse of the disc (figure 19) contains scales and tables,¹ which are, more or less, common to all astrolabes. Reading from the circumference towards the centre:—

c7.28

¹ Of these, c to j are shown in the appendix on astrology (p. 124).

c7.29

(a) The two upper quadrants are graduated for every three degrees (numbered in the abjad notation), also in degrees, numbered in Arabic numerals from 1 to 90, and in one-sixths of degrees, or every twelve minutes.

c7.30

(b) The periphery of the lower quadrants is graduated by shadow scales—on the left a ‘twelve scale’ and on the right a ‘seven scale.’ (See p. 22.)

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(c) The next complete annulus contains the signs of the zodiac, which are accompanied by graduations down to intervals of twelve minutes.

c7.32

(d) Next are the *manzils* or ‘mansions of the moon.’

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(e) The planets—twelve to each sign—with graduations for every 2½ degrees.

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(f) The planets—nine to each sign—with graduation for every 3° 20.’

c7.35

(g) The planets—five to each sign—with their limits or terms indicated.

c7.36

(h) The planets—seven to each sign—at intervals of 4⅔ degrees.

c7.37

(i) The planets—three to each sign. These are the ‘faces’ of the particular sign.

c7.38

(j) Again three planets to each sign.

c7.39

(k) Another pair of shadow scales.

c7.40

(l) Separated from the others by the smaller shadow scales (k) are the names of the European months, with a scale showing the days of each month, etc. The instrument was made in A.D. 1680 and correctly indicates that spring commenced on March 10th.

c7.41

20. The central part of the disc consists of a projection of a sphere and a table of sines.² These are illustrated in figure 22, where the quadrant OAB forms the table of sines. The arc AB is divided into degrees, and, from every point of division lines are drawn perpendicular to OA. The radius OB is divided into 60 equal parts, and lines are drawn parallel to OA. In the diagram sin 40° reads 39°, i.e., 39/60 or ·65, but the instrument itself is more accurate than this. The radius OD is divided into sixty equal parts, and, through each point of division, circles, also passing through the points A and C, are drawn. These arcs are orthogonal projections of great circles inclined to the meridian C¹A¹ of the sphere ABCD. For example, the arc passing through the division numbered 50 represents a circle on the sphere inclined to the meridian at an angle φ, such that sin φ = 50/60 (= ·835). Now the arc 50 in the quadrant CB touches the horizontal line 50 which cuts the arc BA at 56½, therefore φ = 56½ [actually sin 56½ = ·8339].