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## Mut̲h̲allat̲h̲

(419 words)

(a.), also mut̲h̲allat̲h̲a , pl. always mut̲h̲allat̲h̲āt , triangle; it forms the first category of plane surfaces bounded by straight lines ( al-basāʾiṭ al-musaṭṭaḥa al-mustaḳīmat al-k̲h̲uṭūṭ (cf. al-K̲h̲wārazmī, Mafātīḥ , 206). Following Euclid’s Elements, i, ʿΟρος 24-9, the Arab mathematicians classify triangles from two points of view: either according to the sides ( ḍilʿ , pl. aḍlāʿ ) into equilateral ( al-mut̲h̲allat̲h̲ al-mutasāwī ’l-aḍlāʿ , in Euclid τρίγωνον ὶσόπλευρον), isosceles ( al-mut̲h̲allat̲h̲ al-mutasawi ’l-ḍilʿayn , τρίγωνον ἰσοσκελές), and scalene ( al-mu…

## Muḳābala

(2,323 words)

(a.), a technical term in a number of different disciplines. 1. In astronomy. Here it corresponds to Gr. διάμετρος, in the Almagest άχρόνυκτος, Lat. oppositio, the term for the opposition of a planet and the sun or of two planets with one another. In opposition, the difference in longitude between the two heavenly bodies is 180°; while the modern use is to take no note of the deviations of latitude from the ecliptic, al-Battānī expressly emphasises ( Opus astronomicum, ed. Nallino, iii, 196) that we can only have the true muḳābala when both bodies are either in …

## al-Kayd

(2,021 words)

, name of a fictitious star, defined in the Mafātīḥ al-ʿulūm (ed. van Vloten, Leiden 1895, 229) as nad̲j̲m naḥis fi ’l-samāʾ lā yurā wa-lahū “ḥisab maʿlūm yustak̲h̲rad̲j̲u bihī mawḍiʿuhū , “an ill-omened ¶ invisible star in the heavens, having a known ephemeris from which its position can be derived”. It is not mentioned in LA and TA. Although occurring in at least one oriental text printed in Europe ( Anonymus Per sa de Siglis Arabum et Persarum , ed. and tr. J. Gravius, London 1648), it seems to have escaped the attention of historians of astronomy…

## Asṭurlāb

(4,885 words)

or aṣṭurlāb (Ar.; on the vocalization see also Ibn Ḵh̲allikān, no. 779; idem, Būlāḳ, no. 746), Astrolabe. The word was derived from the Greek ἀστρολάβος or ἀστρολάβον (ὄργανον), name of several astronomical instruments serving various theoretical and practical purposes, such as the demonstration and graphical solution of many problems of spherical astronomy, the measuring of altitudes, the determination of the hour of the day and the night, and the casting of horoscopes. In Arabic the word Asṭurlāb when used alone always means the flat or planisphe…

## al-D̲j̲awzahar

(865 words)

or al-D̲j̲awzahr , technical term occurring in Arabic and Persian astrological and astronomical texts. 1. It indicates primarily the two lunar nodes, al-ʿuḳdatāni , i.e., the two diametrically opposite points of intersection between the moon’s orbit and the ecliptic: the ascending node or “head”, raʾs , and the descending node or “tail”, d̲h̲anab ( scil . of the ¶ dragon, al-tinnīn ). In many cases it refers only to the “head”; in some mss. a special word, nawbahr , is used for the “tail” [see below]. The word Ḏj̲awzahar, though explained differently in the Mafātīḥ al-ʿulūm

## Minṭaḳat al-Burūd̲j̲

(5,982 words)

, also minṭaḳat falak al-burūd̲j̲ , are all used in Arabic to designate both the zodiac and the ecliptic. Strictly speaking, the zodiac is a “belt”, or “zone”, of the sky extending up to 6° (more correctly, 7°) north and south of the ecliptic due to the inclination of the orbits of the planets from the latter, while the ecliptic is a great circle in the sky running through the middle of the zodiacal belt and representing the path of the sun ( ṭarīḳ/ṭarīḳat al-s̲h̲ams ) in her apparent annual revolution. The knowledge of both the zodiac and the ecliptic was …

## al-Nahr

(858 words)

, the constellation of the River (Eridanus). It corresponds to the ΠοταμόΣ, Flumen, Amnis of the ancients (cf. Aratos, Φαινόμενα, l. 358; Geminus, Εἰσαγωγή; Ptolemy, Almagest). Aratos observes (l. 360) — probably one of the first to do so, — that the river of heaven represents Eridanus (’ΗριδανόΣ, river of the morning? or river of darkness, of the west?) turned into stars, into which Phaeton, son of Helios, fell, struck by the thunderbolt of Zeus, after his unsuccessful attempt to ride to heaven. [The opinions of the Gr…

## al-Mus̲h̲tarī

(734 words)

, the planet Jupiter, Pers. Hurmizd < Aurmazd (Ahura-mazdāh). The name of the planet is in Sumerian S̲h̲ulpaʾe, later also Mulu-babbar “the white star” (= Μολοβαβαρ in Hesychios; cf. Meissner, Babylonien und Assyrien, Heidelberg 1925, ii. 404); in the later Accadian period it is always identified with the numen supremum Marduk (Biblical Merodach). In Hebrew it is called Ṣedeḳ, in Greek — just as among the Babylonians, as the symbol of the highest deity — ὁ τοῦ ΔιὸΣ ἀστήρ. As a synonym of al-Mus̲h̲tarī we find (e. g. in Ḥadīt̲h̲) the name Bard̲j̲īs (cf. Lisan al-ʿArab, vii. 323). The Arab ast…

## al-D̲j̲abr wa ’l-Muḳābala

(2,372 words)

, originally two methods of transforming equations, later the name given to the theory of equations (algebra). The oldest Arabic work on algebra, composed ca. 850 A.D. by Muḥ. b. Mūsā al-K̲h̲wārizmī [ q.v.], consistently uses these methods for reducing certain problems to canonical forms; al-K̲h̲wārizmī’s work was edited with English translation by F. Rosen, London 1831. A revision of Rosen’s text is badly needed, cf. S. Gandz, The Mishnat ha Middot , in Quellen u. Stud. z. Gesch. d. Math. , Abt. A: Quellen, 2, 1932, 61 ff.; the translation is arbitrary and often wrong, not the…

## Zuhara

(816 words)

, the planet Venus. The Arabic name is derived from the root z-h-r meaning “to shine, be radiant”, appropriate for the brightest planet whose magnitude can reach 4.4; perhaps in consequence of this, it was sometimes referred to as the white planet ( LA). Z-h-r does not seem to have cognates referring to Venus in other ancient languages. Its Persian name is ( A) nāhīd . From Antiquity it was well known that the “morning” and “evening” stars were in fact the same planet, and that this planet, Venus, stayed fairly close (within 48°) to the sun. According to ancie…

## Abū Kāmil S̲h̲ud̲j̲āʿ

(1,240 words)

b. Aslam b. Muh. b. S̲h̲ud̲j̲āʿ al-Ḥāsib al-Miṣrī , next to Muḥ. b. Mūsā al-Ḵh̲wārizmī [ q.v.] the oldest Islamic algebraist of whose writings we still possess some remains; they entitle us to place him among the greatest mathematicians of the Islamic Middle Ages (for the development of Islamic algebra see al-d̲j̲abr wa ’l-muḳābala ). Through Leonard of Pisa and his followers he exercised considerable influence on the development of algebra in Europe and no less great was the impact of his geometrical writings (algebraic treat…

## Ḥabas̲h̲ al-Ḥāsib al-Marwazī

(1,087 words)

, Aḥmad b. ʿAbd Allāh , one of the most important and interesting figures in early Islamic astronomy, hailing from Marw, but living in Bag̲h̲dād. The sobriquet “Ḥabas̲h̲” (“the Abyssinian”) is nowhere explained; it may refer to the dark colour of his skin. While the Fihrist (p. 275) mentions only that he reached the age of 100, Ibn al-Ḳifṭī ( Taʾrīk̲h̲ , 170) gives more detailed information on his life and the various stages of his scientific activity. According to him, he lived in the reigns of al-Maʾmūn and al-Muʿtaṣim, which is co…

## Falak

(2,078 words)

, Sphere, in particular the Celestial Sphere. a. Etymology and semantic evolution. The word falak (pl. aflāk ) occurs already in the Ḳurʾān with the specific significance “celestial sphere” (xxi, 34 “it is He who has created night and day, the Sun and the Moon, each of which moves in its own sphere”; similarly xxxvi, 40). Etymologically and semantically it has a long history: it can be traced back to Sumerian origins, where the stem bala (≷ * pilak ) already has the meaning “to be round” or also “to turn around”. In Akk. it appears as pilakku , which denotes the whorl o…

## Nūr

(2,653 words)

(a.), light, synonym ḍawʾ , also ḍūʾ and ḍiyāʾ (the latter sometimes used in the plural). 1. Scientific aspects According to some authors, ḍawʾ ( ḍiyāʾ) has a more intensive meaning than nūr (cf. Lane, Arabic-English dictionary, s.v. ḍawʾ); this idea has its foundation in Ḳurʾān, X, 5, where the sun is called ( ḍiyāʾ and the moon nūr. The further deduction from this passsage that ḍiyāʾ is used for the light of light-producing bodies (sun) and nūr on the other hand for the reflected light in bodies which do not emit light (moon), is not correct, if we remember the primiti…

## Naẓīr

(99 words)

, Naẓīr al-samt (a.), Eng. and Fr. nadir, the bottom, the pole of the horizon (invisible) under the observer in the direction of the vertical, also the deepest (lowest) point in the sphere of heaven. The nadir is the opposite pole to the zenith [see samt al-raʾs ]. The word naẓīr (from naẓara “to see”, “to observe”) originally (and generally) means the point diametrically opposite a point on the circumference of a circle or the surface of a sphere; we find muḳābal as a synonym of naẓīr in this general meaning [see also muḳābala ]. (W. Hartner)

## al-Mus̲h̲tarī

(745 words)

, the planet Jupiter, Pers. Hurmizd < Aurmazd ( Ahura-mazdāh ). The name of the planet is in Sumerian S̲h̲ulpaʾe , later also Mulu-babbar “the white star” ( = Μολοβαβαρ in Hesychios; cf. Meissner, Babylonien und Assyrien , Heidelberg 1925, ii, 404); in the later Akkadian period it is always identified with the numen supremum Marduk (Biblical Merodach). In Hebrew it is called Ṣedeḳ , in Greek — just as among the Babylonians, as the symbol of the highest deity — ὁ τοῦ Διὸς ἀστήρ. As a synonym of al-Mus̲h̲tarī we find (e.g. in Ḥadīt̲h̲ ) the name Bard̲j̲īs (cf. Lisān al-ʿArab , vii, 323). The Arab ast…