1. CC

2. Formerly “Arabian astronomy” – too limiting geographically Used to be slighted coverage – “caretakers” for Greek works, esp. Almagest Now called “Islamic astronomy” – lands where Islam was dominant Not all were Muslims – some Christians, Jews, and others Significant improvements of Ptolemy’s work, spatial orbits – but nothing fundamentally different; still appearances Islamic Astronomy

4. Chronology of Islamic Astronomy 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 Hijrah – flight from Mecca to Medina = Year 1 of Islamic Calendar Baghdad founded House of Wisdom, Baghdad: translation of Greek works Almagest translatedal-Khwarizmi (HW): zij; algebra Thabit ibn Qrra (HW): trepidation al-Battani: zij, sines etc. al-Sufi (HW): Book on Fixed Stars Ibn Yunus: Hakemite Tables, obs’ns al-Haytham: Optics; On Configuration of World al-Zarqala: Toledo Tables Cairo Obs. al-Tusi: Tusi couple, Maragha Obs. Taqi al-Din Istanbul Obs. Alfonsine Tables Ilkhanic Tables, Ulugh Beg Samarkand Obs. Sultanic Tables Omar Khayyam: zij Isfahan Obs. KEY  Arabia, Iraq, Syria  Persia (Iran)  Egypt  Uzbekistan  Spain  Turkey AD Ibn al-Shatir, Rectification of Principles Sack of Baghdad

5. Islamic world common language = Arabic Mecca spiritual center of Islamic world “Islamic astronomy” basically started in Baghdad, founded 762 by Caliph al-Man’sur Man from India who could predict eclipses (773)  founding of House of Wisdom in Baghdad by Caliph Harun al-Rashid (building upon al- Man’sur’s palace library), expanded by al- Ma’mun Islamic Astronomy

6. Islamic world had two main uses for astronomy:  in religious practice  as basis of astrology Astrology unacceptable to strict Muslims -- BUT… Astrology used by:  rulers to guide decision-making  physicians in medical practice Islamic Astronomy

7. Astronomy in Religious Practice Calendar – month, year Prayer (salat or salah) – times, direction Astronomy in Religion

8. Calendar originally lunar – synodic months Later lunisolar, with empirical intercalation Muhammad decreed return to pure lunar calendar: 12 synodic months or 354 days Ramadan “floats” in Western calendar Month starts with hilal – first time Moon visible Astronomy in Religion

9. HILAL Very thin crescent immediately following new Moon Not easy to spot even in clear skies of Middle East Difficult to catch where skies cloudier – need formula tied to Sun-Moon distance Astronomy in Religion

10. HILAL Very thin crescent immediately following new Moon Not easy to spot even in clear skies of Middle East Difficult to catch where skies cloudier – need formula tied to Sun-Moon distance Astronomy in Religion

11. Pray at certain times of day (schematic): (King) Astronomy in Religion

12. Crude estimate of times based on shadow lengths: (King) Astronomy in Religion

13. Later developed formula using spherical trigonometry Functionary at mosque to calculate times -- Muwaqqit Also calculate direction to Kaaba, shrine in Mecca = qiblah; again spherical trigonometry (Hoskin) Astronomy in Religion

14. Table with times for candles to be extinguished at Cairo mosque for each day of year Astronomy in Religion

15. Tables with times all over world calculated using computer; chapter on history Astronomy in Religion

17. Alignment of Kaaba Sides directly face four wind directions Main axis towards rising point of Canopus, a bright star in southern sky Shorter axis roughly aligned with summer solstice sunrise = winter solstice sunset (King) Astronomy in Religion

18. House of Wisdom (Bayt al-Hikmah) Islamic Astrology

19. House of Wisdom (Bayt al-Hikmah) Originally translation from Greek, Syriac, and other languages into Arabic Later a center for scholarship and research = Institute for Advanced Studies Translation of Almagest in 827 Under al-Ma’mun measurement of length degree of latitude  Earth’s circumference = 26, 560 mi (7% too high) Islamic Astrology

20. Zij: Planetary Tables and Other Matter Modeled along lines of Ptolemy’s Handy Tables for practical use Later ones more elaborate, additional material: mathematical tables star catalogues (usually Ptolemy’s corrected for precession) collections of observational data on eclipses, conjunctions, etc. More than 200 known, probably many more! Islamic Astrology

21. al-Khwarizmi Associated with House of Wisdom Zij al-Sindhind earliest surviving – based on Hindu, pre-Ptolemy Greek, and Persian elements Also wrote early book on algebra (Arabic name al-Jabr); first to solve equations using general methods His name basis of term algorithm in mathematics, computer science Islamic Astrology

22. Thabit ibn Qurra = Tobit Associated with House of Wisdom Contributed to mathematics and physics (statics) Criticized Ptolemy for inconsistencies between Almagest and Planetary Hypotheses Identified with concept of trepidation – variation in rate of precession and obliquity Islamic Astrology

23. Trepidation Suggested by two errors of Ptolemy:  underestimation of rate of precession as 1°/100 yr instead of 1°/72 yr  overestimation of obliquity as 23° 51’ instead of 23° 34’ Persisted through Copernicus’s time Islamic Astrology

24. Trepidation Red circle highlights location of equinox Islamic Astrology

25. Muhammad al-Battani = Albategnius Not associated with House of Wisdom (Raqqa, in Syria) Az-Zij as-Sabi included advance of Sun’s apogee, accurate eccentric for orbit Length of year 365.2406; 365.2412 but for error of one day in Ptolemy (actual 365.2422); obliquity 23° 35’ (actual 23° 27’) Introduced half-chords, now known as sines, in tables; rigorous formula for spherical triangle Islamic Astrology

26. Solar Orbit To account for variable motion along ecliptic and unequal length of seasons, used eccentric: (Hoskin) apogee (farthest point from Earth) longitude of apogee Direction of advance =eastwards Islamic Astrology

27. Referenced extensively (almost two dozen times) by Copernicus later Islamic Astrology

28. Abd al-Rahman al-Sufi = Azophi Worked at court of Isfahan in Persia (Iran) Book on Fixed Stars – star catalogue with positions, magnitudes, and colors as well as pictures of constellations Mix of Ptolemaic and old Arabian constellations Positions based on Ptolemy, not new; magnitudes new Many star names are from Arabs, not necessarily original with al-Sufi Islamic Astrology

29. Fish are from old Arabian constellation Standing figure is Andromeda, a princess in Greek mythology Stippled area in front of the larger fish’s nose is M 31, the Andromeda Galaxy – visible to naked eye; few others noted (Hoskin, Cambridge Illustrated History) Islamic Astrology

30. Perseus, hero from Greek mythology, slaying Medusa, a Gorgon, to rescue Andromeda Star Algol (al-Ghul) in Medusa’s head (now known to be variable – close binary system) (Hoskin, Cambridge Illustrated History) Islamic Astrology

31. Abd al-Rahman ibn Yunus Astrologer of newly-founded city of Cairo Hakemite Tables (Zij al-Hakim al-Kabir) named for Caliph who sponsored his work (one of several) Tables unusual – contained extensive compilation of observations, his and earlier – conjunctions, eclipses Observed with somewhat large instruments Islamic Astrology

32. Ibn al-Haytham = Alhazen Also associated with Cairo and Caliph al- Hakim Book on Optics important, influenced Roger Bacon and Kepler later; based on experiments Doubts on Ptolemy – criticized equant, eccentric; Ptolemaic system mathematical, not physical On the Configuration of the World – geocentric, homocentric similar to Aristotle Islamic Astrology

33. Ibn al-Zarqali = Azarqueil/Arzachel Resided in Toledo, in Spain Toledo Tables – based on al-Khwarizmi and al- Battani as well as Ptolemy Toledo Tables included descriptions of instruments and their use Translated into Latin by Gerard of Cremona, became popular in Europe Islamic Astrology

34. Invented two new instruments: saphea arzachelis (latitude-independent or universal astrolabe), equatorium (maybe Greeks earlier) Islamic Astrology

35. (Wikipedia) Equatorium Used to obtain positions of Sun, Moon, and planets Based on Ptolemaic models Worked like analog computer, replacing hand calculations using tables Particular example shown is for Saturn Islamic Astrology

36. Omar Khayyam Persian; famous for poem The Rubaiyat of Omar Khayyam Noteworthy for mathematics, including work on parallel lines anticipating non-Euclidean geometry Also worked in philosophy and astronomy, the latter in connection with calendar reform In other words, a polymath! (but not mentioned in Hoskin!) Islamic Astrology

37. The Rubaiyat of Omar Khayyam (FitzGerald translation – best known) A Book of Verses underneath the Bough, A Jug of Wine, a Loaf of Bread--and Thou Beside me singing in the Wilderness-- Oh, Wilderness were Paradise enow! The Moving Finger writes: and, having writ, Moves on: nor all thy Piety nor Wit Shall lure it back to cancel half a Line, Nor all thy Tears wash out a Word of it. ***

38. Connected with Isfahan Observatory 1074- 1092 Work led to Zij al-Malikshahi (named for Sultan Malik Shah I) and Jalali calendar (collaboration of eight including Khayyam) Jalali calendar based on Sun’s passage through 12 divisions of ecliptic, some elements from India Alternative to Islamic lunar calendar; solar = more practical for agriculture etc. Islamic Astrology

39. Months of lengths ranging from 29 to 32 days; vary year to year Average length of year in Jalali calendar 365.24219858156 days vs. actual 365.2422464 Calendar continued in use for centuries; with slight modification up to present in Iran Islamic Astrology

40. Alfonsine Tables Sponsored by King Alfonso X (“Wise”) of Leon and Castile; Christian but studied under Muslim and Jewish scholars Developed by team led by Isaac ben Said and Jehuda ben Moses Cohen Completed 1272 Became “gold standard” for planetary tables in Europe for next three centuries Islamic Astrology

41. Nasir al-Din al-Tusi Religious scholar and mathematician at al- Alamut fortress until its fall to Mongols under Hulagu il Khan (grandson of Genghis Khan) Became astrologer to Hulagu; persuaded him to fund Maragha Observatory near Tabriz (Iran) Devised Tusi couple in 2-d and 3-d versions to eliminate eccentric, describe motion in latitude Established Maragha School of planetary theory Islamic Astrology

42. Tusi couple Converts rotary motion to oscillation along a line – linear motion in superlunary region! Can be employed in variety of ways one element in Maragha School models Islamic Astrology

43. Tusi couple and eccentric Dashed circle is path followed by point on small circle. It is offset by diameter of small circle. Earth could be at center of solid circle and displaced from center of dashed one. HOWEVER – Angular rate seen at C is constant.

44. Result of work at Maragha was Ilkhanic Tables (1272; named for Hulagu) Eliminate equant by adding secondary epicycle 3-d Tusi couple to model motion in latitude Almost exactly contemporaneous with Alfonsine Tables but not nearly as well known in Europe Islamic Astrology

45. Ibn al-Shatir Followed al-Tusi by about a century Served as muwaqqit at large mosque in Damascus Worked in Maragha tradition; published improved models in Rectification of Principles Eliminated equants by adding epicycles, also added epicycle to correct problem with Ptolemy’s lunar model (2× distance variation) Tested models against observations -- empirical Islamic Astrology

46. Ibn al-Shatir’s Lunar Model Uses secondary epicycle instead of Tusi couple Achieves good fit to Moon’s motion in longitude without Ptolemy’s 2× variation in distance (Wikipedia) Angular diameter related to distance – spatial orbit, not just motion in longitude Islamic Astrology

47. Shortcomings of the Ptolemaic System According to Ancients Moon’s distance varied by factor of 2 in model; angular size varies only ~10%. line of syzygy (new, full) (Pannekoek) (rotated 90° for easier comparison) Islamic Astrology

48. Ibn al-Shatir’s Solar Model Uses secondary epicycle (“director”), not Tusi couple Center of deferent uniform around O Director uniform retro around A  AB || OCT True Sun 2× around B Matches Ptolemy’s motion in longitude Angular diameter observations  relative distance; spatial orbit! director (Saliba) (not accurate)

49. Ibn al-Shatir’s Model for Mercury Modern: Mercury’s orbit largest eccentricity of planets Mercury’s angular diameter too small – can’t see disk Multiple epicycles as before to eliminate equant, eccentric Good fit to motion in longitude

50. Some features of al-Shatir’s models showed up in Copernicus’s work later Question of whether Copernicus knew al- Shatir’s models – transmission from Maragha through Constantinople? Byzantine Greek documents (scholar at Maragha) containing the Tusi couple in Italy by 15 th century Lunar models nearly identical Still considered inconclusive! Islamic Astrology

51. Ulugh Beg Grandson of Tamerlane (Timur), Turko-Mongol conqueror Governor of Samarkand (Uzbekistan), succeeded father as Sultan after death Built up Samarkand as intellectual center – started madrasah (university or institute) Interested and knowledgeable about astronomy as well as mathematics Islamic Astrology

52. Inspired by Maragha, established Samarkand Observatory which produced Zij i-Sultani = Sultanic Tables (1437) Tables had improved parameters for planetary orbits, obliquity, length of year Included sine and tangent tables Uniquely, included star catalogue with (mostly) newly measured positions (992, combined with few from al-Sufi), not just rehash of Ptolemy’s Islamic Astrology

53. Observatories in the Islamic Period Few major observatories, some small ones (e.g. Baghdad) Only three major observatories lasted a couple of decades: Two major observatories were laid waste only a few years after their inception:  Isfahan (virtually unknown)  Maragha (most famous)  Samarkand (second most famous)  Cairo  Istanbul Islamic Observatories

54. Maragha Observatory Established by Nasir al-Din al-Tusi in 1259, right after Sack of Baghdad (and not too long before Gaocheng) Sponsored by Hulagu il Khan, Mongol ruler Large staff drawn from many lands: Persia (Iran), Syria, Anatolia (Turkey), and China -- not just Muslims; al-Urdi, al-Shirazi also important Extensive library of 40,000 volumes Islamic Observatories

55. Large cylindrical observing tower Fairly large (radius 14 ft) mural quadrant Armillary sphere 5 ft radius Islamic Observatories

56. After al-Tusi’s death in 1274 was succeeded by son Declined thereafter, abandoned by ca. 1350 Ruins visited by Ulugh Beg, inspired him to establish Samarkand Islamic Observatories

57. Samarkand Observatory Established by Ulugh Beg in 1429 Somewhat modeled after Maragha, influenced by Maragha School Directed by al-Kashi, Beg’s protegé and a mathematician (law of cosines) Instruments of large size – continued trend in Islamic astronomy to increase precision Not always the case! Islamic Observatories

58. Armillary Sphere Human figures indicate size Armillary made of bronze (?), support frame made of wood Larger radius = longer baseline  higher precision BUT – Instrument bends under own weight  distorts scale  loss of accuracy! (Hoskin, Cambridge Illustrated History) Islamic Observatories

59. Mural quadrant 125-ft radius (Tycho’s much smaller) View in meridian plane Russian model of observatory Islamic Observatories

60. Mural quadrant 125-ft radius ground level Islamic Observatories

61. Samarkand mural quadrant Islamic Observatories

62. Effectively ended when Beg assassinated by son in 1449 Less influential than Maragha Islamic Observatories

63. Istanbul Observatory Established by Taqi al-Din in 1577; almost exactly contemporaneous with Uraniborg, Tycho Brahe’s first observatory Sponsor was Ottoman Sultan Murad III; expected high-quality astrological advice Equipped with large armillary sphere, mural quadrant, triquetrum, astrolabe, saphea, hand- held quadrant, and sextant Islamic Observatories

64. Which instruments do you recognize? Islamic Observatories

65. Comet appeared shortly after completion; Sultan requested advice. Taqi al-Din’s astrological prediction of Sultan’s glorious victory over the Persians failed badly, followed by plague and deaths of some important people. Clerical opponents of astrology prevailed, and observatory was destroyed in 1580. Islamic Observatories

66. Isfahan Observatory Isfahan capital of Seljuk Turk Empire in 11 th century (S of Tehran) Observatory established 1074 by Sultan Malik Shah I and vizier; Omar Khayyam invited to be director First major observatory? Not much seems known about instruments Islamic Observatories

67. Ended after assassination of vizier and death of Sultan, 1092; widow cut off support Islamic Observatories

68. Cairo Observatory Vizier of Caliph started construction of large observatory in 1120. Work continued after his death, but new vizier was executed in 1125 by Caliph for “communicating with Saturn.” Observatory was demolished and staff had to “flee for their lives” (Hoskin). Islamic Observatories

69. Torquetrum Devised to convert between three coordinate systems: altazimuth, equatorial, ecliptic Analog computer Invented by Abu Muhammad Jabir ibn Aflah = Geber around middle of 12 th century in al-Andalus (Spain) Islamic Observatories

70. Islamic Astronomy -- Summary Observations – improved accuracy over Greeks, partly by using larger-sized instruments Theory – more sophisticated than Ptolemy, eliminated perceived problems with his models Advances in theory and analysis of observations connected with advances in mathematics; somewhat linked – astrologers and mathematicians Disconnect between mathematical models and physical reality – reluctant to pursue physics of orbits

71. (Of course, neither did Europeans before Kepler!) See beginnings of what would become two significant institutions in the West:  Universities – foreshadowed by madrasahs such as the one at Samarkand (Greeks had academies)  Research observatories – large scale, with major instruments, staff, library as at Maragha Islamic Astronomy

72. Accuracy Comparison – Tropical Year All estimates predate the invention of the telescope around 1608. Approximate dateLength (days) (Thurston) Islamic Astronomy

73. Accuracy Comparison -- Obliquity * * Obliquity changes over time; error based on contemporary value. Obliquity Islamic Astronomy