Babylonian Astronomy Teije de Jong Astronomical Institute ‘’Anton Pannekoek” University of Amsterdam 4 May 2011 IAC2011 History of Astronomy 1 Literature 1. A. Pannekoek, De Groei van ons Wereldbeeld, Wereld-bibliotheek, Amsterdam (1951) [sections 1 - 6 treat Babylonian astronomy] 2. O. Neugebauer, The Exact Sciences in Antiquity, Brown University Press, Providence (1957) [stimulating reading on Babylonian mathematics and astronomy in chapters I,II, III & V] 3. A. Pannekoek, A History of Astronomy, Interscience Publishers, New York (1961) [this is an English translation of ref. 1 with notes and references added; the Babylonian astronomy chapters 1 - 6 are somewhat outdated] 4. B.L. van der Waerden, Science Awakening II, Noordhoff, Leiden (1974) [very clear presentation of Babylonian astronomy in chapters 2, 3, 4, 6 & 7] 5. O. Neugebauer, History of Ancient Mathematical Astronomy (3 Vols.), Springer, Berlin (1975) [Vol. 1, Book II presents detailed account of Babylonian Astronomy] 6. J.P. Britton and C.B.F. Walker, Astronomy and Astrology in Mesopotamia, in Astronomy before the Telescope, ed. C.B.F.Walker, British Museum Press, London (1996) [quite readable overview of Babylonian astronomy] 4 May 2011 IAC2011 History of Astronomy 2 1 Literature (continued) 7. J. Evans, The history and practice of ancient astronomy, Oxford University Press (1998) [sections on Babylonian astronomy interspersed throughout the book] 8. H. Hunger and D. Pingree, Astral sciences in Mesopotamia, Brill, Leiden (1999) = HP [authorative textbook on Babylonian astronomy] 9. J.M. Steele, A Brief Introduction to Astronomy in the Middle East, Saqi, London (2008) [first two chapters deal with Babylonian astronomy] Required reading for the Exam: Steele (ref. 9), p. 9 - 65 4 May 2011 IAC2011 History of Astronomy 3 Outline • Introduction • Time keeping: the calendar • Diaries: the observational database • Astronomical intermezzo • Sirius and the solar year • Cycles: – the Saros – Planetary periods • Normal stars: the ecliptic coordinate system • Planetary theory: ephemerides 4 May 2011 IAC2011 History of Astronomy 4 2 Introduction • Mesopotamia (Babylonia and Assyria) = area between the rivers Euphrates and Tigris (present-day Iraq; see #6) • Mesopotamian culture documented on ~ ½ million clay tablets containing texts in cuneiform script • Cultural continuity over more than three millennia in spite of many changes in rulership (see slide #7) • City of Babylon main centre of astronomical activity (see slide #8), but also Nineveh, Uruk and Sippar • At present ~ 2000 tablets with astronomical texts translated and interpreted 4 May 2011 IAC2011 History of Astronomy 5 The Near East in Antiquity 4 May 2011 IAC2011 History of Astronomy 6 3 Historical Overview • < 2000 BC: Sumerians, Mesopotamian city-states • ~2000 BC – ~1500 BC: Old-Babylonian period, terminated by Hittite invasion • ~1500 BC – ~1200 BC: Cassite rule • ~1200 BC – 627 BC: Assyrian period; terminated with destruction of Nineveh (royal library of Assurbanipal) • 627 BC – 538 BC: New Babylonian period • 538 BC – 330 BC: Persian rule • 330 BC – 311 BC: Greek rule • 311 BC – 129 BC: Seleucid period • 129 BC – 226 AD: Arsacid period 4 May 2011 IAC2011 History of Astronomy 7 Babylon during Nebuchadnezzar II (604 – 561 BC) 4 May 2011 IAC2011 History of Astronomy 8 4 Introduction (continued) • Astronomy plays a central role in Babylonian religion; the priesthood attempts to read the will of the Gods from the heavens, and advises the king accordingly • This provides a strong motivation to study the sky (see “ziggurat’ in slide #10) • Astronomical knowledge and astrological lore intermingled and practiced by the same priests/scholars • Climatic conditions excellent for astronomical observation (2π steradian sky and < 100 mm precipitation/year • Continuity in astronomical activity over > 2000 years • Exceptional mathematical talent (sexagesimal place-value number system) 4 May 2011 IAC2011 History of Astronomy 9 Ruin of the ziggurat of Borsippa 4 May 2011 IAC2011 History of Astronomy 10 5 Cuneiform script and number system • Cuneiform script was developed by the Sumerians in southern Mesopotamia over the period 3300 – 2500 BC • Initially used for administrative purposes; later also for literary texts • Written with reed stylus on wet clay tablets • Gradually evolving from pictographic signs to the well-developed script that was used in Mesopotamia until ~ 0 AD (see slide #12) • The Sumerian logograms were kept for writing Akkadian (Semitic language) in Babylonia and Assyria when Sumerian was no longer spoken (after ~1800 BC) • Akkadian was gradually replaced as a spoken language by Aramaic during the 1st millennium BC but the cuneiform script was kept for writing religious and scientific texts until ~ 75 AD • Sumerian and Babylonian number system (see slides #13 & 14) – Place-value system – Fractions – Base 60 (sexagesimal) 4 May 2011 IAC2011 History of Astronomy 11 Development of cuneiform script 4 May 2011 IAC2011 History of Astronomy 12 6 The sexagesimal number system 4 May 2011 IAC2011 History of Astronomy 13 A numerical example 4 May 2011 IAC2011 History of Astronomy 14 7 Time keeping: the calendar 4 May 2011 IAC2011 History of Astronomy 15 The Babylonian calendar • Calendar of importance for civil organisation, agriculture and religion • Babylonian calendar is lunar calendar with 12 months of 29 or 30 days • New month begins on day of first (re-)appearance of lunar crescent after sunset • Day is reckoned from sunset to sunset (still the case in derivative Jewish and Arabic calendars) • Month I synchronized with Spring Equinox (barley harvest) 4 May 2011 IAC2011 History of Astronomy 16 8 4 May 2011 IAC2011 History of Astronomy 17 The Baylonian calendar - 2 • Year of 12 lunar months is about 11 days shorter than solar year, so seasons run through the year • Solution: intercalation = occasionally adding of extra month to correct for this (month VI2 or XII2) • Until about 600 BC irregular intercalation by decree of the King • King Hammurabi (~1800 BC) to Sin-iddinam: “This year has an additional month. The coming month should be designated as the second month Ululu [month VI], and wherever the annual tax had been ordered to be brought to Babylon on the 24th of the month Tashritu [month VII] it should now be brought to Babylon on the 24th of the second month Ululu.” 4 May 2011 IAC2011 History of Astronomy 18 9 Babylonian calendar - 3 • On tablet II of astronomical compendium MUL.APIN (ca. 1000 BC) we find the following intercalation prescription: “If KAK.SI.SÁ (= the arrow = Sirius) becomes visible on the 15th of Du’uzu (month IV) this year is normal”. “If KAK.SI.SÁ (= the arrow = Sirius) becomes visible on the 15th of Abu (month V) this year is a leap year”. • Commentary: – Heliacal rising of Sirius occurs each year on the same solar day (same position w.r.t. Sun) – Babylonian lunar calendar synchronized to solar year by using date of heliacal rising of Sirius to decide about intercalation of additional month 4 May 2011 IAC2011 History of Astronomy 19 The Babylonian calendar - 4 • From ~ 500 BC onwards regular intercalation in 19-year cycle with 7 additional months (after year2/monthXII, y5/mXII, y8/mXII, y10/mXII, y13/mXII, y16/mXII & y19/mVI) • In earlier periods often intercalation of month VI rather than month XII (see slide #21) • Intercalation scheme of 19-year cycle such that heliacal rising of Sirius always falls in month IV • From the equality 19 tropical years (365.2422 days) = 235 synodic months (29.53059 days) we find that the 19-year cycle is a little more than 2 hours too long Æ after 400 years only 2 days! • 19-year cycle provides calendar that is comparable in accuracy to the Julian calendar (43 BC – 1582 AD) • Continuous calendar record from ~750 BC onwards 4 May 2011 IAC2011 History of Astronomy 20 10 The Babylonian calendar - 5 Dates (Julian calendar) of the 1st day of the Babylonian month (see slide #22) from 604 – 595 BC; 4/2 = 2 April, 5/1 = 1 May, etc. (from Parker & Dubberstein 1956). Notice that around 600 BC most intercalations involved second Ululu’s (month VI) 4 May 2011 IAC2011 History of Astronomy 21 Babylonian calendar - 6 The logograms give the reading of the cuneiform symbols representing the month names. They consist of the abbreviations of the Sumerian month names of the Nippur calendar. 4 May 2011 IAC2011 History of Astronomy 22 11 Astronomical Diaries: the observational database 4 May 2011 IAC2011 History of Astronomy 23 Astronomical Diaries • “Astronomical Diaries” is a class of texts containing records of observations and computations made during a period of half a year (6 or 7 months) • The oldest Diary so far dated was recorded in 652 BC; the latest Diary dates from 61 BC • The systematic recording probably started in 747 BC, the first year of the reign of Nabû-nāsir, since cuneiform “reports” of lunar eclipses grouped in 18-year (“Saros”) periods and extracted from the Diaries begin in that year • About 1200 (fragments of) tablets with in total ~ 400 months of recorded observations from 652 BC – 61 BC (~5% of all nights in that period) are preserved 4 May 2011 IAC2011 History of Astronomy 24 12 Astronomical Diaries - 2 The Diaries contain the following information: – Dates of planetary phases (first/last visibility, stationary points) – Dates on which moon and planets pass “normal stars” – Times of rising and setting of the moon – Dates of solstices and equinoxes (computed) – Dates of Sirius phenomena (often computed) – Dates of sign entries of planets (> 3rd century BC) – Atmospheric phenomena (wind, rain, halos, etc.) – Miscellaneous information (historic events, market prices, sickness, river levels, etc.) 4 May 2011 IAC2011 History of Astronomy 25 VAT 4956: an Astronomical Diary from 568 BC 4 May 2011 IAC2011 History of Astronomy 26 13 VAT 4956: an Astronomical Diary for 568 BC - 2 #1 Year 37 of Nebukadnezar, king of Babylon. Month I, (the 1st of which was identical with) the 30th (of the preceding month), the moon became visible behind the Bull of Heaven; [sunset to moonset:] ...