HISTORICAL ECLIPSES AND EARTH'S ROTATION

Transcription

1 HISTORICAL ECLIPSES AND EARTH'S ROTATION F. Richard Stephenson University of Durham CAMBRIDGE UNIVERSITY PRESS

2 Contents Principal Symbols 1 Variations in the length of the day: a historical perspective Introduction The solar day First speculations on variations in the Earth's rate of rotation Discovery of the lunar secular acceleration Early attempts to explain the Moon's secular acceleration Discovery of the solar secular acceleration Fluctuations in the mean motions of the Moon, Sun and planets The introduction of a theoretically invariant time-system Short-term fluctuations in the Earth's rotation The Julian and Gregorian calendars 29 2 Tidal friction and the ephemerides of the Sun and Moon Introduction Evaluation of the lunar tidal acceleration on TT Transits of Mercury Artificial satellite data Lunar laser ranging Selected value for n The constancy of the lunar tidal acceleration The tidal acceleration of the Earth's spin Lunar and solar tidal dissipation Ephemerides of the Sun and Moon Solar ephemeris Lunar ephemeris Conclusion 42 3 Pre-telescopic eclipse observations and their analysis Introduction Observational requirements for determining AT in the pre-telescopic period Alternatives to eclipses in the pre-telescopic period 44 ix xv

3 x Contents Equinox and related measurements Close planetary conjunctions Occultations of stars and planets by the Moon Further remarks Historical eclipses Cause of eclipses Solar eclipses Lunar eclipses Eclipse observations which are of value in the investigation of AT Sources of data Solar eclipse observations and their reduction to AT Total and annular solar eclipses Solar eclipses which, although large, were not quite central Timed solar eclipse contacts Solar eclipse magnitudes Observations that the Sun rose or set eclipsed Records which merely note the occurrence of a solar eclipse Lunar eclipse observations and their reduction to AT Timed lunar eclipse contacts Observations that the Moon rose or set eclipsed Estimates of the degree of obscuration of the Moon at moonrise or moonset Conclusion 91 4 Babylonian and Assyrian records of eclipses Introduction The Babylonian lunar eclipse records in the Almagest Investigation of the Babylonian lunar eclipses cited by Ptolemy Historical background to the astronomical cuneiform texts Decipherment of the cuneiform texts Origin and classification of the Late Babylonian astronomical texts The Babylonian calendar Techniques used in dating observational tablets Units of time 'Lunar sixes' Observation and prediction of eclipses Observations Predictions Assyrian records of solar and lunar eclipses Conclusion 127

4 Contents xi 5 Investigation of Babylonian observations of solar eclipses Introduction The total solar eclipse of BC 136 Apr Timed observations of solar eclipses Estimates of solar eclipse magnitude Solar eclipses occurring near sunrise or sunset A possible allusion to a total solar eclipse in the Babylonian Religious Chronicle Conclusion Timed Babylonian lunar eclipses Introduction Lunar eclipses for which only a single contact measurement relative to sunrise or sunset is preserved Measurements expressed to the nearest degree Other less accurate measurements (to the nearest 5 or 10 degrees) Eclipses for which two contact measurements relative to sunrise or sunset are extant Three or four timings relative to sunrise or sunset preserved (total eclipses only) Eclipse maxima timed relative to sunrise or sunset (partial eclipses only) First contacts timed relative to culmination of stars Conclusion Untimed Babylonian observations of lunar eclipses: horizon phenomena Introduction Moon rising or setting eclipsed Estimates of the proportion of the Moon obscured at its rising or setting Conclusion Chinese and other East Asian observations of large solar eclipses Introduction Records of solar eclipses from the Shang dynasty The Chou dynasty and Warring States period (c BC) The Ch'in and Han dynasties (221 BC to AD 220) From the San-kuo to the Sui dynasty (AD ) The T'ang dynasty and Wu-tai period (AD ) The Sung, Kin and Yuan dynasties (AD ) 250

5 xii Contents 8.8 The Ming dynasty (AD ) Korea Japan Conclusion Other East Asian observations of solar and lunar eclipses Introduction General remarks on recorded eclipse timings Double hours and their subdivisions Night-watches and their divisions Estimates of lunar azimuth Accuracy of early eclipse predictions Sources of timed observations and terminology Careful solar eclipse timings recorded in Chinese history Solar eclipse timings recorded in sources other than the Yuan-shih Solar eclipse timings recorded in the Calendar Treatise of the Yuan-shih Lunar eclipse timings Lunar eclipses timed in fifths of a night-watch Lunar eclipses timed in double hours and marks Azimuth measurements for lunar eclipses Estimates of solar eclipse magnitude Sun rising or setting eclipsed Moon rising or setting eclipsed Estimates of the proportion of the Sun or Moon obscured at its rising or setting Other records of lunar eclipses Conclusion Records of eclipses in ancient European history Introduction Solar eclipses analysed by Fotheringham Other ancient reports of large solar eclipses Greek lunar eclipse observations recorded in Ptolemy's Almagest The moonrise eclipse of BC 331 Sep 20/ Conclusion Eclipse records from medieval Europe Introduction Historical sources Chronological discussion Interpretation of observations of large solar eclipses 381

6 Contents xiii 11.5 Place co-ordinates Eclipses which were central at a known location Detailed descriptions Brief reports of total eclipses Eclipses which were definitely partial, yet very large Detailed records which are deficient in some way Timed solar eclipse contacts An eighth century occultation of Jupiter by the eclipsed Moon Conclusion Solar and lunar eclipses recorded in medieval Arab chronicles Introduction Chronicles and chroniclers Date conversion Records of total and near-total solar eclipses Other records of large solar eclipses Sun eclipsed near sunrise or sunset Moon eclipsed near moonrise or moonset Selected records of total lunar eclipses Conclusion Appendix: Arab chronicles consulted Observations of eclipses by medieval Arab astronomers Introduction Sources of data Motives for observation Calendrical remarks Observational techniques References to large solar eclipses in astronomical treatises Solar eclipse times recorded by Ibn Yunus Lunar eclipse times recorded by Ibn Yunus Solar and lunar eclipse timings recorded by al-battani and al-biruni Solar magnitude estimates Rising and setting phenomena Conclusion Determination of changes in the length of the day Introduction Timed and untimed observations Lunar and solar tidal friction Constant non-tidal component Variable non-tidal component 509

7 xiv Contents 14.6 Further discussion of timed observations Changes in the LOD Geophysical discussion Concluding remarks 517 Appendix A Timed data 518 Appendix B Untimed data 524 References 527 Acknowledgements 539 Index of eclipse records 540 Index of places of observation 549 Name index 551 Subject index 554