al-Qanun al-Mas'udi (The Mas'udic Canon)

"Al-Qanun al-Mas'udi" is the great work of Abu al-Rayhan al-Biruni on astronomy, which the editor of the Beirut edition calls the largest encyclopaedia of astronomy, geometry and geography of its age. ³ Al-Biruni wrote it in 421 AH (1030 CE), the editor says, and dedicated it to the sultan Mas'ud ibn Mahmud of Ghazna. ^{4 5}

Al-Biruni opens with praise of God and of the sultan Abu Sa'id Mas'ud son of Yamin al-Dawla Mahmud, says that the rank of learning is the noblest in his eyes, and so chose to serve his library, "marked by wisdom", with a "canon for the craft of the stars" ennobled by his name — al-Qanun al-Mas'udi. ^{6 2} Yaqut reports, as the editor quotes, that the sultan rewarded him with an elephant-load of silver, which al-Biruni returned to the treasury as something he did not need. ⁷ Another version given by the editor has him return three camel-loads of silver, saying he served knowledge for its own sake and not for money. ³

The editor quotes al-Biruni's preface: he did not follow earlier zij-makers, who confined themselves to tabular settings and concealed how they had founded their rules, but joined to every procedure its reasons and stated what he had worked out himself, so that the reader could approve or correct rather than imitate. ^{1 8} The editor describes how he discussed proofs, repeated observations more than once and invited correction of his own slips. ¹

The book has eleven books (maqalat) totalling 142 chapters, covering the observations and theories of his age and the results of earlier civilisations and of al-Biruni's contemporaries. ¹ Book 2 treats the histories of prophets and kings from Adam to al-Biruni's own day for their bearing on calendars, the well-known eras — the Hijra, the era of Alexander, the era of Yazdgird — the years of the Indians and the Jews, the Christian fasts and feasts, "the days held great in Islam among the Arab months", and the feasts of the Persians in their Zoroastrian days, such as Tirgan. ^{8 9} In the chapter on the great days al-Biruni states that the days the Law requires to be fixed are the first of Ramadan and of Shawwal for the fast and its breaking, and the first of Dhu al-Hijja for the pilgrimage and the sacrifice, and that they depend on sighting the crescent, not on calculation; the Ashura fast, he says, was superseded by the fast of Ramadan. ¹⁰

Book 3 deals with chords, sines, shadows and the spherical sector; in it al-Biruni drew up sine tables for every quarter degree instead of every degree, wishing he could have done so for every minute, and devised a law of interpolation to improve the use of tables. ^{11 12 13} Book 4, in twenty-six chapters, covers the obliquity of the ecliptic, ascensions, terrestrial latitudes, the meridian, the azimuth, the hours and the cardines, with a table for the latitude of Ghazna. ^{14 15 16 17}

In the chapter on the greatest declination al-Biruni describes the observing instrument, compares Ptolemy's with that of the Arabs, and gives the results of the Indians, the Greeks and his contemporaries, among them Abu Mahmud al-Khujandi at Rayy, whose colleague admitted to al-Biruni that the instrument had been faulty at one of the solstices. ¹⁸ He then records his own observations, made four times: before 387 AH, in 407 in Khwarazm, and in 410 and 411 at Ghazna. ¹⁸

The editor lists seven manuscripts, the oldest the Bodleian copy at Oxford dated 475 AH, then Paris (501), the Millet (531) and Bayezid (before 536) libraries in Istanbul, Tübingen (before 562), the British Museum (570) and the Egyptian Dar al-Kutub (673). ⁵ Dairat al-Ma'arif al-Uthmaniyya at Hyderabad printed it in 1954 from all seven, with the Bayezid copy as base. ⁵ The Cairo copy has a story the editor tells: copied by Muhammad ibn Mas'ud al-Sinjari the astrologer in Jumada II 673, it was offered in 1912 by an itinerant bookseller to an official named Mahmud Mas'ud, bought by the deputy minister of education Abu al-Futuh Pasha, and acquired by Dar al-Kutub after his death. ¹