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(a.), a term in Islamic astronomy denoting the sighting of the lunar crescent. In this article, astronomical aspects are covered. Muslim astronomers from the 2nd/8th century onwards performed calculations to predict the visibility of the lunar crescent, of particular importance for the fixing the beginning and end of Ramaḍān and the festivals [see hilāl , i. In religious law; ʿīd; ramaḍān ; ṣawm ; taʾrīk̲h̲ ]. Over the centuries, the techniques and visibility conditions that they used became more sophisticated. Even the simplest procedures involved a knowledg…

(a.), morning or evening twilight, the periods between daybreak ( al-fad̲j̲r or ṭulūʿ al-s̲h̲afaḳ ) and sunrise ( ṭulūʿ al-s̲h̲ams ) and between sunset ( g̲h̲urūb al-s̲h̲ams ) and nightfall ( mug̲h̲īb al-s̲h̲afaḳ ). These are of special importance in Islamic ritual because they relate to three of the prayers [see ṣalāt and mīḳāt , i]: the fad̲j̲r prayer is to be performed as soon as possible after daybreak and must be completed before sunrise, the mag̲h̲rib prayer begins as soon as possible after sunset, and the ʿis̲h̲āʾ prayer as soon as possible after nightfall. Al-Bīrūnī [ q.v.] gives an…

(a.), or taʿdil̄ al-ayyām bi-layāl̄ihā , the equation of time, a fundamental notion in mathematical astronomy. Times derived from observations of the sun [see mīḳāt ] need to be corrected by a function which takes into consideration the fact that the true sun does not move on the celestial equator but on the ecliptic [see minṭaḳat al-burūd̲j̲ ] and the fact that its motion on the ecliptic is not uniform. This correction, which varies throughout the year, is the equation of time, and it was tabulated in Islamic astronomical handbooks [see zid̲j̲ ]. Since tables of …

(a.), in planetary astronomy the correction or equation (corresponding to medieval Latin aequatio ) applied to mean positions of the sun, moon and planets to derive the true positions [see ḳamar ; s̲h̲ams. i. ; taḳwīm ; zīd̲j̲ ]. Muslim astronomers generally tabulated these functions in the same way as Ptolemy had done in the Almagest [see baṭlamiyūs ] but occasionally introduced more extensive sets of tables to facilitate the tedious application of more than one equation (as in the case of the moon and planets). (D.A. King) Bibliography E.S. Kennedy, Solar and lunar tables in early…

(a.), azimuth or direction, a term in frequent use in Islamic astronomy. It is usually applied to the direction of a celestial object measured on the horizon, determined by the arc of the horizon between the east- or west-points and the foot of the vertical arc through the celestial object. The Arabic plural al-sumūt gave rise to the term azimuth and its equivalents in numerous European languages. But whilst in mediaeval astronomy the azimuth was usually measured from the east- or west-points, in modern astronomy it is measured clockwise from the north point. The complementary arc measu…

, Abū ʿAlī al-Ḥasan b. ʿAlī , astronomer of Mag̲h̲ribī origin who worked in Cairo. In ca. 680/1281-2, he compiled a compendium of spherical astronomy and astronomical instruments entitled Kitāb D̲j̲āmiʿ al-mabādiʾ wa ’l-ghāyāt fī ʿilm al-mīḳāt , which is perhaps the most valuable single source for the history of Islamic astronomical instrumentation. In this work, which exists in several manuscript copies, al-Marrākus̲h̲ī presented a detailed discussion of the standard problems of spherical astronomy [see mīḳāt. 2. Astronomical aspects], and then dealt with different ki…

(a.), literally, “quarter”, in Islamic astronomical terminology, quadrant. The kind of large mural quadrant ( libna ) with a graduated altitude scale described by Ptolemy (see baṭlamiyūs ] was used by a series of Muslim astronomers over the centuries. Descriptions exist of i.a. those used in the Damascus observations in the early 3rd/9th century ( ca. 5 m in radius), by the astronomer Ḥāmid b. K̲h̲iḍr al-K̲h̲ud̲j̲andī at Rayy in the late 4th/10th century (called al-suds al-Fak̲h̲rī , radius ca. 20 m), and in the early 9th/15th century observatory of Ulugh Beg [ q.v.] at Samarḳand (radius ca…

(a.), lit. “leg” or “thigh”, used in various senses in Islamic mathematics and astronomy. Thus, for example, sāḳ means the foot of a compass, the perpendicular of a right-angled triangle with horizontal base, or the equal sides of an isosceles triangle. Another term for the foot of a compass is rid̲j̲l , and ḍilʿ is also used for any side of any triangle. (See further ʿilm al-handasa , in Suppl.). In astronomy [see nud̲j̲ūm ] sāḳ may refer to a star that is in a leg of a constellation figure representing a person or an animal, as in sāḳ al-asad or sāḳā ’l-asad ¶ (dual) for either or both of α Boo…

(a.), declination, an important notion in spherical astronomy. Declination is a measure of the distance of a celestial body from the celestial equator. Muslim astronomers tabulated either the declination and right ascensions of stars or their ecliptic coordinates [see maṭāliʿ ]. Also of concern to them was the solar declination, mayl al-s̲h̲ams . They distinguished two kinds of solar declination, al-mayl al-awwal, the distance δ1 of the sun from the ecliptic measured perpendicular to the celestial equator, and al-mayl al-t̲h̲ānī , the distance δ2 of the sun from the ecliptic m…

(a.), the term used in mediaeval Islamic scientific texts for the magnetic compass. The earliest references to the magnetic compass in the Islamic written sources have been surveyed by E. Wiedemann in mag̲h̲nāṭīs . 2. to which see also the addenda in volume IX. To these sources may now be added: 1. A treatise on the magnetic compass (called ṭāsa ) used for finding the ḳibla , compiled by the Rasūlid Yemeni Sultan al-As̲h̲raf ca. 690/1290 (first studied by P. Schmidl in 1994); see PL V. There is no mention of any deviation of the compass needle from the meridian, but w…

, in Islamic science an astronomical handbook with tables, after the models of the Sāsānid Persian Zīk -i S̲h̲ahriyār , the Indian Sindhind [ q.v.], and Ptolemy’s Almagest and Handy Tables [see baṭlamiyūs ]. A typical zīd̲j̲ might contain a hundred folios of text and tables, though some are substantially larger than this. Most of the relevant astronomical and astrological concepts are clearly explained in the Tafhīm of al-Bīrūnī [ q.v.]. The history of Islamic zīd̲j̲s constitutes a major part of the history of Islamic astronomy [see ʿilm al-hayʾa ]. i. Etymology Arabic zīd̲j̲ (pl. zīd̲j̲ā…

b. Muḥammad b. Maʿrūf, sometimes given the nisbas al-Dimas̲h̲ḳī, al-Ṣahyūnī or al-Miṣrī, the most important astronomer of Ottoman Turkey, b. Cairo or Damascus in 927/1520-1 or 932/1525 (the sources are not consistent), d. Istanbul, 993/1585. He studied theology in Cairo, served as ḳāḍī in Nābulus, and in 979/1571 was appointed müned̲j̲d̲j̲im bās̲h̲i̊ in Istanbul. He was largely responsible for persuading the Ottoman Sultan Murād III to build an observatory in Istanbul. This was achieved in 987/1579. However, the building wa…

(a.), literally “that which rises”. 1. Astronomical aspects. Al-ṭāliʿ is that point of the ecliptic which is rising over the horizon at a given moment, called the ascendent or horoscopus (and sometimes, incorrectly, the horoscope); see the diagram in maṭāliʿ . The determination of the ascendent is necessary in mathematical astrology [see nud̲j̲ūm , aḥkām al- ] before one can calculate the instantaneous positions of the 12 astrological houses ( al-buyūt ); with these determined, one can then investigate in which houses the sun, moon and five na…

(a., mifʿāl form from w-ḳ-t , plural mawāḳīt ) appointed or exact time. In this sense the term occurs several times in the Ḳurʾān (II, 185; VII, 138, 139, 154; XXVI, 37; XLIV, 40; LVI, 50; LXXVIII, 17). 1. Legal aspects. In ḥadīt̲h̲ and fiḳh, the term is applied to the times of prayer and to the places where those who enter the ḥaram are bound to put on the iḥrām . For the latter meaning of the term, see iḥrām. Although some general indications for the times at which some ṣalāt s are to be performed occur in the Ḳurʾān (cf. II, 239; XI, 116; XVII, 80; XXIV, 29), i…

(a.), literally, correcting between the two lines, an expression used in Islamic mathematics and mathematical astronomy for interpolation. Muslim scientists used linear and non-linear procedures for calculating intermediate values in mathematical and astronomical tables. (D.A. King) Bibliography J. Hamadanizadeh, A survey of medieval Islamic interpolation schemes, in D.A. King and G. Saliba (eds.), From deferent to equant. Studies... in honor of E.S. Kennedy, New York 1987, 143-52. See also King, Ibn Yūnus’ Very Useful Tables for reckoning time by the sun, in Archive for Hist…

(in English normally “Mecca”, in French “La Mecque”), the most sacred city of Islam, where the Prophet Muḥammad was born and lived for about 50 years, and where the Kaʿba [ q.v.] is situated. 1. The pre-Islamic and early Islamic periods Geographical description. Mecca is located in the Ḥid̲j̲āz about 72 km. inland from the Red Sea port of Jedda (D̲j̲udda [ q.v.]), in lat. 21° 27′ N. and long. 39° 49′ E. It is now the capital of the province ( manātiḳ idāriyya ) of Makka in Suʿūdī Arabia, and has a normal population of between 200,000 and 300,000, which …

(a.), the rising point of a celestial body, usually a star, on the local horizon. This concept was important in Islamic folk astronomy [see anwāʾ and manāzil on some aspects of this tradition], as distinct from mathematical astronomy [see ʿilm al-Hayʾa ], because it was by the risings and settings of the sun and stars that the ḳibla ¶ [ q.v.] or direction of Mecca was usually determined in popular practice. The terms used for the rising and setting points of the sun were usually mas̲h̲riḳ and mag̲h̲rib , maṭlaʿ being generally reserved for stars. The directions…

(a.), sundial. This term and sāʿa s̲h̲amsiyya are used in modern Arabic, but in mediaeval Islamic times horizontal sundials were referred to either as ruk̲h̲āma , lit. “marble” or basīṭa , lit. “flat”, and vertical sundials as munḥarifa , lit. “inclined”. The gnomon was usually called s̲h̲ak̲h̲ṣ , s̲h̲āk̲h̲iṣ or miḳyās . One expression of the Muslim concern with timekeeping and regulating the times of prayer [see mīḳāt ] was an avid interest in gnomonics, the theory and practice of sundial construction. Muslim astronomers made substantial c…

(a, pl. of maṭlaʿ ), ascensions, an important concept in mediaeval spherical astronomy and astronomical timekeeping [see mīḳāt ]. Ascensions represent a measure of the amount of apparent rotation of the celestial sphere, and are usually measured from the eastern horizon, hence the name ascensions. Two kinds were used: (1) right ascensions, or ascensions in sphaera recta; and (2) oblique ascensions, or ascensions in sphaera obliqua [see also falak and maṭlaʿ ]. (1) Right ascensions refer to the risings of arcs of the ecliptic over the horizon of a locality with latit…

(a.), the name given to the markings of a universal stereographic projection which underlies a family of astronomical instruments serving all terrestrial latitudes. The standard astrolabe [see asṭurlāb ] contains a series of plates for different latitudes. Originally, on Greek astrolabes and the first Islamic astrolabes, these served the seven climates of Antiquity [see iḳlīm ]. However, already in the 3rd/9th century specific latitudes were selected and sometimes lists of localities served by these would also be engraved on th…