Astronomies and Cultures in Early Medieval Europe by Stephen C. McCluskey


6258241e9c53a8b-261x361.jpg Author Stephen C. McCluskey
Isbn 978-0521778527
File size 148.9MB
Year 2000
Pages 252
Language Englisch
File format PDF
Category astronomy



 

The lrish Paschal conrroversy The Paschal controversy in England 6 7 Observing the celestial order - monâstic timekeeping Monastic prayer and âstronomy The celestial order The astronomy of De cursu stellarum Monastic timekeeping after De cursu IIO Astronomy in the liberal arts Late Roman learning Antique learning in Ostrogothic Italy Astronomy in the Visigothic court r17 r22 r23 PART 8 tlz 92 THREE THE HARVEST ro ro4 OF MËDIEVAL ASTRONOMIES The fusion of astronomical traditions Astronomy and court culture The reemergence of astrology I3I r40 r45 r49 r57 The encounter of Arabic and Latin astronomies r65 Pracrical astronomies at C6rdoba and Gorze r66 The astrolabe 17r All things in number and'measure r8o The rebirth of Ptolemaic astronomy r88 r88 r90 Translators and translations (Jniversities and the new leaming The corpus astronomicum The introduction to astronomy r92 - De sphaera Computus and the calendar Observing the heavens - instrument texts The theory of the planets - Theoica planetarum Astronomy outside the universities The legacy of early medieval âstronomies Bibliography Index Figures IOI rt4 Teaching computus The revival of the liberal ars 9 97 99 r93 rg8 202 203 204 zo6 r Claimed astronomical alignments at Stonehenge z The Greek model of the universe 3 Ptolemy's epicyclic model 4 Ptolemy's physical planetary rnodel 5 Mithras slaying the primordial bull 6 Nativity and the Adoration of the Magi 7 Calendar with planetary deities 8 Schema of the Calendar of Coligny 9 Calendar of Coligny (detail) Io Calendar from a Christian shrine I I Seasonal feasts in the Calendar of Coligny rz Carolingian illustration of the course of the Sun 13 Altar of Rome and Àugustus at Lyons t4 Personiflcation of the Sun rj The constellation Crux maior 16 Northern constellations setting at the latitude of Tours 17 Exaltation of the Cross 18 The five circles of the world tg The constellation Cygrrus 20 Spacing of the planetary spheres 2r The latitudes of the planets 22 The stellar mântle of Emperor Henry II (detail) 23 T-O map and Paschal rota 24 Cosmic symbolism of the number four zs The back of an astrolabe z6 The front of an astrolabe 209 229 vl1 page 13 r9 2t zJ 43 44 47 5J S6 57 59 6z 73 r03 t07 ro8 r09 tz6 r36 r37 r38 r42 r55 r56 172 173 ; Abbreuiatioyls Preface The real meâsure of Christian religious culture on a broad scale must be the degree to which time, space, and ritual observances câme to be defined and grasped essentially in terms of the Christian liturgical year. AASS BCPMA BL BN BOT CCCM CCM John van Engen' Acta Sanctorum (Pais) Beitriige zur Ceschichte der Philosophie fles Mittelalters (Münster Brirish Library Bibliothèque Nationale Bedae opera ile tempoibus, (Cambridge,, C o rpu s Chis ti ano rum, C o n t i n u a t i o Me Mass., rg43) dlieu alis (Turnholt) (§i.Ur.ri i e s La t i n a (T.orrrfroiJi Lat in aru n (Be rlinll Corpus Consuetudinum Monasticarum CCSL C o rp u s Ch r i s t i a n o ru m, CIL CIMRM Corpu s In s cri p r i on um Corpus Insaiptionum et Monumentorum Religionis '- Mithriacae (The Hague, CLM Se ô- 1956) Codex Latinus Monacensis CSEL Corpus Scriptorum Ecclesiasticorum DSB EETS Leipzig) Dictionary of Scientfic Biography (New y.r.L,y Earÿ English Text Sociery publicatior,o, HAMA Otto Neugebater, A HMML Loeb MGH I ir r:r::, Latitto** (Vienna, prague, and 1iâraorl of_Anciett, Mathematical Astronomy @erlin, Heidelberg, and New york, ,._.i Hill Monasric Manuscripr Library 2 t J' Loeb Clasical Library (London and C;r-664ge, Mass.) Monumenta Germaniae Histoica (Berliraq Hrrr.rir.., and Leipzig). The parts of this series have been abhr,Jatea as follows: Auct. cap. PG i. W.) Antiq. Auetores Antiqubsinryri Conc. Capitularia Concilia Epp. Epistolae I*ges nationum C?i"wanicarum Poetae SS Jcnpîores yt PL Patrologia Craeca (Pais) Patrologia Latina (P ais) RIG Recueil des Inscriptions latini Aeuii t(çoro1;ni re s re ru modern scientists, firmly devoted to the advancement of knowledge, spend much of their time passing on what they know to their students. Thus when we look at the early Middle Ages, we should not consider that the only alternatives were progress or stagnation; rather, they were progress, preservation, or decline. Our question then is not what contributed to progress in âstronomy, for episodes of progress were few.3 Instead, we will ask what fore- of astronomy and shaped the continuation and rene\Mal of astrtoromical practice and knowledge from the fourth to the thirteenth centuries' Poet. Scr. Rer. Merov. o be of value. This emergence of scholarly interest after centurieo of apparent stagnation defines the paradox. This book attempts to explain that seeming contradiction by examining early medieval knowledge and practices, attitudes, and instirutions reflecting on the heavens. In my discussion of medieval astronomies I have abandoned two common assumptions about âstronomy. The first is that of taking the rapid change of modern science as normal and measuring other sciences against some standard of progress. For progress is only halfofthe picture ofscience; its goal is notjust to expand the realm of the known, but to preserve what is known against error. This is especially true in the natural knowledge of traditional cultures,' but even stalled the decline Leges. S^cn Early medieval science presents an irritating historical paradox. The conventional view of science in the Hellenistic and Roman periods portrays a declining tradition typified by supertcial handbooks and encyclopedias. conversely, the reemergence of science in'W'estern Europe began with the active search by medieval scholars for Arab astronomy as earÿ as the tenth century. Yet such active inquiry presupposes knowledge and interest; we seek out only what we already know to m me*èroui ngirurum r. :. .1. (palrrlr) lluloises Van Engen, "Christian Middle Ages," P. 543See, for example, the essays in Wilson, Rationality; Horton and Finnegan, Modes of Thought; arnà Hollis and Ltkes, Rationality and Relativism. Progress'\r/as not âs rare as suggested by the stereotype of the "Dark Ages" or by one witer who summarized the achievemens of medieval astronomers in a chapter consisting of four blank pages. Henry Smith Willi?|ms, The Gredt Astronomers (New York: Simon & Schuster, r93o), pp' 99-loz' I owe this reference to Owen Gingerich. ix .§(le already have the skeleton of aR mewer, known to ânyone who hes ever surveyed medieval history. The christian church, we are told, and particularly the monasteries, preserved classical learning. But can we be more p.a.ira, can rù/e determine what kinds of asrronomies survived through the early Middle Ages? Can we find what practical or social or ideological functions tlrese astronomies had that made them useful to influential groups in early medieval society and therefore worth presenring? Finally, can \Me find how these astronomies influenced the search for ancient leaming? To whar extent can we put meat on these bare bones to see the fuIl countenance of early medieval astronomy? In seeking to flesh out the skeleton of early medieval astronomy \Me are forced to challenge the second coûunon assumption: that âstronomy can be treated as a single discipline whose practitioners share the same concems, raise the same questions, and employ the same methods. Rather than limit ourselves to the kind of astronomy that has left its mark on modem practice, I prefer to consider as astronomy any âttempt by the members of a communiry to establish a framework that makes their observations of the heavens intelligible. Since the principal restriction that this definition proposes is that astronomy must be tied, ar some point, to observations of the heavens, it leaves room for a wide range of astronomies. Thus we must begin by distinguishing among medieval asrronomical traditions, identiÿing the problems they dealt with and the asrronomical techniques,they employed. There are many di{ferences that can help us distinguish different kinds of astronomies, but for the early Middle Ages a few seem most significant. Is the âstronomy based purely on observation, or does it use mathematical techniques to predict future observable phenomena? If it does use calculations are they bÀed on geometrical and trigonometric models or on simple arithmetic? Does it trace the conrinuous motion of bodies, or does it determine the times or places at which indiüdual celestial events occur? If it is concemed with events do these recur once a year or month, and so define a calendar, or every day so as to mark particular times in a day? \vhich celestial bodies does the astronomy consider: the stars' sun, Moon, or other planets?a Applyrrrg these criteria to the early Middle Ages, we can distinguish at least four distinct astronomical traditions. The first kind of âsrronomy we encounrer is an ancient tradition of diüding the year into eight equal parts using simple observations of the rising and setting Sun. The central concern of this astronomy \À/as to determine ritually ,ira .J endrically important dates, but the method was strictly observational. observers noted when the Sun arrived at a particular point as a wây to mark the arrival of 4' I will generally follow mcient tradition and include the Sun and Moon among the seven planets. discussing details I will often need to distinguish the five starlike planets from the nvo great luminaries, the Sun and Moon. I will then refer to them th. oth., prarets or, folrowing 'When Ptolemy, the five planets. Almagest, 9.r-6, r3.r-4. "s dly, Thfu &rtronomy, likc other tnditlonal âEttonomieË, had no thcorctical framework beyond the simple concept of dividing the year into equal e pâËleulü Part§. Easter computus rvas also concerned with determining calendrically and ritually significant dates, the dates of the Paschal Full Moon and of Easter. These were computed using simple arithmetic and the periods of the Julian year, the lunar month, and the week. Although one result was an observable fu]l Moon, these dates were computed using simple arithmetical techniques in which observations of the Sun and Moon had no direct part. Since the method of computus was fundamentally arithmetical, geometriÇal considerations of celestial spheres and circles could also be ignored. This does not mean that practitioners of computus never looked at the sky or considered geometrical models of the heavens. Observations and models were often discussed in the computistical literature to illustrate the celestial motions underlying the arithmetical techniques, but they belong more properly to other astronomical traditions. Monastic timekeeping defined another astronomical tradition, again concerned with determining a ritual time, but here the time was the time of prayer. The techniques employed were observarional, watching the course of the stars until they arrived at particular places that marked the time to pr. ay; at fint there was little in the way of a theorefical framework to govern these observations. This began to change early in the ninth century as instruments began to supplement simple unaided observations, bringing with them an implicit geometric model of the heavens and an increasingly quantitative meâsurement of the passage of time. The {inal tradition is the one comrnonly taken as defining ancient and medieval astronomy, the geometrical astronomy of the quadriüum. The central concern of this tradition was the continuous motion of the heavens within a geometrical model of the universe. This tradition gave rise to ttvo related branches. One was a qualitative cosmological model of a geocentric universe with rotating spheres carrying rhe stars and planets. The other was a predictive geometrical model of circles and epicycles and the mathematical techniques derived from that model to compute the positions of the stan, Sun, Moon, and other planets as functions of time. This tradition \À/as not designed for, and in {act is not ideally suited for, determination of the arrival of parricular days or moments that we have seen in the other three traditions. Any âttempt to treat medieval astronomy as a single tradition would pose ân ,rrrtr"..rr"ry dilemma. Either we would have to omit major elements of medieval âstronomy as outside our concern, or we would find ourselves forcing elements from different traditions into a historically or theoretically inappropriate framework. Nonetheless, while distinguishing among these astronomies we also must remember that no intellectual tradition exists in total isoladon; there are instances where these astronomies interact. Computus texts employ horizon observations to illustrâte computistical concepts, while school commentaries in the liberal arts clraw on data fiom computigticel tcxB, Dcipite such interaction§, more ir to bc gained from considering these four traditions separately than from indiscriminately lumping them together. It is not just these astronomies, their questions and techniques, that concern us. Having identified these different astronomical traditions we find that they flourished in different cultural contexts, made specific contribucions to the communities in which they flourished, and reflected and reinforced the values of the communities that supported them. The traditional solar calendar, in both its prehistoric pagan and its medieval Christian form, was closely tied to local communities. Crirical dates in a traditional solar calendar based on local horizon observations were transformed into feasts of important local saints that were sponsored by local elites and represented local, rather than universal, centers of temporal and spiritual pov/er. Assemblies for their feasts on the tradirional solar mid-quarter days animated and enriched the local centers of those cults. 'while Easter computus also focused on religious rituals, ity presentation of a uniform technique for calculating the date of a univenal feast reflected the centriltzing tendency and desire for uniformity of ritual on the part of the church hierarchy. This standard technique was spread by monasric and cathedral schools and by the carolingan court, which also disseminated other elements of ritual uniformity. Monastic timekeeping, like monasticism itse[ combined elements of local autonomy with an underÿing principle of order regulared by a sacred rule. The divinely ordained order of the stars wâs observed over local landmarlcs following local practices, yet all was aimed at following rhe same orderly round of prayer. During late ântiquity the asrronomy of the liberal arts had lost contact, in the .w.est, Latin with its powerful calculating techniques founded on spherical geometry and trigonometry. since this tradition could no longer compute the precise circumstances of astronomical phenomena, it had lost its strongest connection to the observable sky. But the image it provided of a well-designed cosmos, and the concept that that cosmos is governed by a universal order, had lasting influence in court circles. To rulers the appeal of this image of universal dominion is obvious. That they chose to study this asrronomy themselves and display it on ritual regalia and in the art they sponsored, so to be seen as wise rulers, suggesrs its value in justiÿing imperial dominion. considering these four traditions, the visage of earry medieval âstronomy becomes richer and more complex. These astronomies not only stimulated the quest for ancient learning from the tenth to the thirteenth centuries, they also provided the framework within which that astronomy was assimilated. problems arising within the practical astronomies inspired the inquiry into and masrery of this newly recovered learning. These traditions, then, are essential not only for an undentandlng of errÿ medieval rcicnce but dro for a eompletc understanding of the development of science in the letcr Itliddle Ages end Renaissance. In dealing with both popular and leaned astronomies, we touch on an increasingly important historiographical issue: the interplay of learned and popular culture, Van Engen has recently surveyed this issue as it applies to the Christianization of western Europe, where the process of conversion is now recognized as a slow adaptation in which Christian and pagan concepts coexisted side-by-side for centuries.r In quite different guise this sâme concern appeârs in discussions of the folk astronomies of the Americas, where traditional âstronomical techniques and their related rituals continued, oftenwith a thin Christian veneer, in native communities.u 'We find similar survivals in early medieval astronomy. Celtic feasts blend into saints' days; pagan constellations are used to determine the times for monastic prayer; quântitative data from Greek asttonomy are employed to compute the date of Easter. The adoption of Christianbeliefs and practices under the influence of preexisting pagan rituals, the adoptionof Mediterraneân geometric astronomy under the influence of traditional techniques, will provide one guiding theme to this discussion. In trâcing this.theme I will be mindtul of the interâctionsxrâmong different groups in society revealed by studies of the Christianization of Europe and of the close relationships between âstronomy, religion, politics, and society revealed by studies of folk astronomies. Just as socialhistorians have drawn insights into the stnrcture of ear§ medieval society from anthropological studies of traditional cultures, so can a historian of science better understand early medieval science by reflecting on archaeoastronomical and ethnographic invesrigations of astronomies in tradirional cultures. As an overview of a few important asptcts of medieval astronomies spanning a millennium, this book cannot claim cornpleteness. Medieval astronomy reminds me of a Mesoamerican jungle: here and there a few mounds indicate the sites of ruins, some of which have drawn explorers, while others remain to be investigated; much however has crumbled intoruin, been looted by scavengers, or lies forever buried. I have tried to find solre pattern in the more readily visible monuments, but no doubt future investigators will examine those I have overlooked and find further paths connecting them. In particular, since the practice of Tstrology only begins to emerge at the end of this period, I have not dug deeply there. Something beyond ThomdLke's monumental survey is still needed before we really understand medieval ashology.T i. 6. 7. Van Engen, "Christian Middle Ages." Broda, "Mesoamerican Âgricultural Calendar." Tester rightly criticized Thomdike and othen riho saw astrology where none was present through It is a commonplace to acknowledgË the inspirâtion of one's colleagues and I am taking something of a new approach, this dcbt is even teachers. Although more âpparent. The question this book oudines has been nagging me since my first year as a graduare student, when the late 'william Stahlman introduced me to folk âstronômies. The tools to attempt ân ans\Mer I owe to David Lindberg and william courtenay, who introduced me to medieval science and philosophy. My general framework of how astronomies, religions, and cultures interact has been refined by discussions with my fiends and colleagues who do archaeoastronomy, especially Anthony Aveni, Johanna Broda, John Carlson, David Carrasco, David Dearbom, and clive Ruggles. As I placed elements of medieval astronomy in that framework a câutionary cornment of the late Ned Zeena, a sun watcher of the tobacco clan at walpi Pueblo, often came to mind. He recognized how I could see what he was doing as âstronomy, but he looked at it as his religion. I have tried to be sensitive to such differences ofperception. One theme of this book is the support of learning through the Middle Ages; the book's appeârance demonstrates that such support continues. This book first took form in 1988, during a sabbatical granted me by west virginia (Jniversity; years later its publication was assisted by a subvention granted by the universiry and its Eberly college of Arts and Sciences. Its completion would have been impossible without the assistance of the librarians and curâtors who granted me access to books and artifacts in their collections, frequently providing me with photographs to illustrate my discussion. I especially thank the tireless interlibrary loan staff of the 'west virginia university Library, who cheerfully and elficiently met my requests for esoteric publications, as well as the librarians at st. vincent Archabbey and college and the universiry of Pittsburgh, ôr their neighborly hospitality. Closer to home my son, Tom, brought order to my boxes of photocopies, my wife, Connie, brought clariry to my writing, and young Rose excused my absences. As the book developed, my students and colleagues commented on earÿ drafts; their questions provoked me to define my argumenr more explicitly. Finally, I must thank the members of the community of medievalists who have edited texts, described arriâcts, and looked in detail at aspects of my problem. The bibliography is not just a tool for those who read this book; it catalogs many of my debts. Perhaps this book will be accepted as partiar payment. "confusion of astrologia [often meaning astronomy] with astrology md the inference to the presence of astrology Êom descriptiorx or representations of the zodiac." Tester,.d History of westem Astrology, pp.vli, r4z. Flint's contention that the needs ofreligious timekeeping led churchmen tô preserve astrology involves inferences of that kind. FknL Magir in Early Mediual Europe, pp. r37, r42. PART ONE The enuironment _fon medieual ûstronomies CHAPTER ONE Astronomies in cultures With regard to virtuous conduct in practical actions and character, [astron- omyl, above all things, could make men see clearÿ; from the constancy, order, symmetry and calm which are associated with the divine, it makes its followers lovers of this divine beauty, accustoming them and reforming their nâtures, as it were, to a similar spiritual state. Ptolemy, Almagest' The lights in the heavens, the Sun and the Moon, the stars and the other planets, lrave enticed people to contemplate them from the beginnings of recorded history.' In the introduction to his great work of mathematical astronomy, the Hellenistic astronomer Claudius Ptolemy (ca. roo-ca. r75) put his finger on one of the timeless appeals of the heavens. The heavens display â constEpcy and an order, â symmetry and a calm, that stand as silent challenges to the transience and discord, the irregularity and turbulence, of the world in which we live. He spoke truly when he declared these characteristics to be divine. Lest I mislead readen who rnay be unfamiliar with Ptolemy, his work, and its influence, he was not primarily concerned with the ethical syrnbolism and import of the orderly motions of the unchanging heavens. Hlis Almagesl was, from beginning to end, a work ofmathematical astronomy, providing detailed geometrical rrrodels of the harmonious motions of the stârs, Sun, Moon, and other planets. Yet the Latin \Mest lost this mathematical astronomy in late antiquiry. The only element of Ptolemy's âstronomy that had any substantial influence through the earÿ Middle Ages was that general concept, which he shared with philosophers and theologians, of the heavenly spheres as a model of order'3 For that reason this book, unlike Ptolemy's, is only peripherally concemed with the theoretical side of astronomy; we will touch on it briefly insofar as we need to know a bit of theory if we are to understand hov/ astronomy \À/as put into practice. Central to my discussion will be the practical aspects of astronomy r. z. Ptolemy, Almagest, t.r. Apparent tallies of the waxing and waning of the Moon have been found on bones dating as earÿ as the thirtieth millennium r.c.; Alexander Manhak, The Roo* oJ Civilization (New York: McGraw-Hill, r97z). But see Francisco d'Erico, "Palaeolithic Lunar Calendars: À Case of Wishful Thinking," Cunent Anthropology, 3o(r98g):Il7-r 18, and Alexander Marshak, "On Wishfirl Thinking and the Lunar Calendr," Cunent Anthropology,3o(r989):4qr-Joo (with a reply by d'Erico). 3. Taub, Ptolemy's Universe, esp. pp. r3J-r53. in both the ntodern and the ancient sensesi the uses of the regular motions of the heavens to reckon the passing of tinres and seasons, and the atteulpts to incorporate those celestial virtues of stability and order into human lives and societies. Our concern with these practical uses to which an understanding of the heavens may be put leads ro an approach which may disturb some students ofmathematical âstronomy. Practical âstronomy is an art, not unlike the art of the potter, the smith, or the healer. As such, it can exist independently of any formal articulation of a mathematical astronomy or a philosophical cosmology. while modern technology depends upon moderrr science and cannot exist without it, even no\M the arts and crafts are on-ly loosely tied to scientific theory. Thus we will more often find ourself discussing astronomical practices concerned with knowing how to determine a specific time, than with astronomical investigations concerned with finding how the heavens move. Tirnes and calendars studies of a broad range of societies have shown that the passâge of the year commonly guides many human activities. The literature is filled with discussions ofpractical calendars that guide the annual cycle ofplanting and harvesting crops or of breeding and slaughtering livestock. This concern with observing natural phenomena in order to mark the tumings of the year came before the rise of settled agricultural communities and the development of writing. Even migratory bands of hunters and gatherers knew in detail the seasonal appearance of wilit plants and animals as local vegetâtion bears its fruit and foliage and as birds, fish, and other animals migrate from place to place with the seasons. But, as social beings humans have more complex needs, and they must know the special times ofgatherings to hunt, to trade, to negotiate, or to celebrate.a This concern to mark special times does not require an astronomical calendar. The migrations of birds and other animals, the flowering of plants and the appearance of their fruit, all mark the arrival of special times. Flowever, the orderly, cyclical recurence of astronomical phenomena proüdes reliable, and widely used, indicators of the passing of the seasons; watching the Sun, Moon, and stars often goes hand in hand with watching other seasonal changes.' It is scarcely ân exaggerâtion to say that âstronomy, botany, and zoology are all natural human activities. These provide a rânge of observable regularities that can be used, and in âct have been used, to mark such special times. I speak consciously of marking times, in the plural, rather than of measuring time, for the essence of a calendar lies in the demarcation of special days a.rà 4. 5. Hudson, "California's First Asrronomers," esp. pp. 55--65. For example, Hesiod, Works and Days, 3fi-go,564-73; Malotki, Hopi Time, pp. 395_4o5; Ted_ lock, Time and the Highland Maya, pp. rSj-rgo. in l reeurring eycle, râther then in the measurement of rn unending flow of undiffercntiated moments of time, There is â temptation to dismiss this attention to special, distinct events, marked by "discontinuous timeindications," as a prinritive antecedent of a "genuine system . . . of timereckoning."n This misses the point; the determination of the arrival of the proper times for recurring practical, social, or ritual activiries is a continuing human problem. What is central is that there is something, some âctiviry, that sets these tlays apart from all others and makes them special. If we are to understand how rnedieval people used astronomy to punctuate the regular flow of the year, we rnust consider the simple âstronomicâl phenomena they used to mark the retum of significant days and to delimit the tuming of the seasons. ieasons that return The Sun is the most potent of heavenly beings, the source of warmth and light, the true fountainhead of life. Its risings and settings delimit the nights and days; its comings and goings mark the tuming of the seasons. In diverse cultures and epochs religious thinkers and philosophers, hunters and farmers, have recognized its crucial importance. The annual changes of the Sun's motion separate seâsons of growth from seasons of dormancy, seâsons of planting from seasons of harvest, seasons when animals are abundant from seâsons when they ere absent. Making order ofthis central aspect ofhuman experience - the changing ofthe seasons tlrew the attention of observers to the heavens. The Sun's annual journey is most clearly divided by its arival at the limits of its travels - the southem limits which mark the onset of winter in the northem hemisphere and the northem limits which mark the onset of summer. Since the Strn is the source of heat and light, its travels not only provide a sign of the changing seâsons but are often seen as causing them as well. Thus its journey is cr»nmonly at the heârt of an observer's attention.T W'e commonly note how the days become longer âs we move towârds summer lnd again become shorter âs we turn towards winter. Usually, the longest day is tuken as marking mid-summer and the shortest day, mid-winter. The day-to-day change, however, is quite small. At Mediterranean latitudes, the length of day'ight changes by only six hours in the six months fromJune to December, an âverage change of only rwo minutes per day. The change becomes imperceptible at the ('xtremes of the Sun's travels in June and December and so is even less suitable to mark the turning of the seasons. Thus, while the length of day indicates the gcneral progress of the seasons, it cannot mark the seâsons precisely without an ;lccurâte means of measuring time. It is not surprising then, that while many societies recognized the changing length of day and night and the complications rr, Nilsson, Primitiye Time-Reckoning, pp. 8-ro, 355-3 j8. 7, Some peoples whose calendars were regulated by the stars came to consider the sumer stan rather than the Sun as bringers of wm weâther. Nilsson, Pdmlrlve Time-Reckoning, pp.r44r45. that it raised for titrrekeeping, rhere bre arenocxsmpler of societiês thât me$urcd this change as a way to determine thrllr the ehanges of the seàsorls. A second comnon sign of the chailchanging mmo,s is the changing height of the Sun at midday. 'w'e are used to feellrfeeling the noontirue sun beat down on our heads in suûuner, whereas v/e cast lolt long lhadows across the snow in winter. llut it is hard to move from this general o[al observation to precise determination of the end of one season and the beginning lüng olthenext. 'w'e can most easily estimate the SudlSun\ changrng height in the sky by considering changes in its shadow. we do not nrrDt need a srandard unit of meâsure; all that-is required is a marked stick or a carefttl leful pace. The precision with which these dayto-day changes in the shadow can be I be observecl increases when larger objects cast the shadows or when more precise rrrilll rneasuring rods are used. As with the duration of daylight, thot, the noonüme height of the sun changes mosr rapidly in spring and autumn, and m;1[ nore slowly in June and December, whicb makes such observations poorly suiteorl.ited lor duectly marking these turning poins in the calendar. Flowever, the changi.hnging length of shadows during the day wæ commonly used to mark the daily pasJipassage oftime. The third principat change in the Suii: Sun's mohons during the year is the changing place of sunrise and sunset. This offerffiers a handy way to find the current position of the Sun. Rather than warching the the sun atnoon, we could equally well watch it rising or setting on the horizon. lyglwe would soon note that the Sun rises Nvice year at any given point berween tiln the nothern and southem extremes of its annual path along the horizon. only nly a shot step separâtes noting that the Sun rises or sets at â particular point on tiln the day of , prrti.olm seasonal event froin the idenrification of that point as a sifa sign of that event. Besides such contingent seasonal events as planting and harveilrrvesting, the extremes, midpoints, and other regular divisions of the Sun's travel cal1 can mark special places on the horizon. t Note that just as a calendar is conce/hcerned wrth special days rather than with the measurement of duration in undifferey'Erentiated units of time, so is a solar horizon calendar concemed with special places hces rather than with the measurement of azimuth in quantifiable angular units. As { As we map special times onto special places, these special places can take on names hres and qualities appropriate to those events. lf a place marks the time to plant beans tans it could become "bean planting mound''; the place of sunset when the blackbirds rrds return could be called "blackbird's wing''i and the place where the Sun rests at tilLt the limits of his travels could be the "Sun's house."8 When the Sun rises ât â sacrel0cred time, and in most cultures the turnings of the seasons rypify such sacred times,,nes, the place where he rises is thereby sanctified. The constant and regular retum ,tm olthe sun to this landmark reinforces the sacred nature of the place and of the sd,e sacred noment in time.e Conversely, since 8. McCluskey, "Historical Archaeoasüonomy,'tmy." pp. jz-4o, 47-4g; Malotki, Hopi Time, pp. 42744r. 9. McCluskey, "Calendars and Symbolism." " these saerecl plâccs surrouncl the centrel place from which the Sun is observed, thet center, whether temple or village, also takes on something of the sacred and becomes, in a sense, the center of the world,'' Thus far, we have considered following the travels of the Sun against a terrestrial framework: a shadow on the ground or a marker on the horizon. But the Sun's seasonal travels through the heavens can also be mapped using the celestial landmarks provided by the stars in the sky. People who watch the stars ât dav/n or in the evening twilight soon come to identify specific bright or conspicuously formed groups of stars. They then notice that different stars are üsible at each season of the year. It is by something close to direct observation, to an intuitive process of association, that we connect the bright stars in Orion with winter." The stars âre not perceptibly warm, like the Sun. There is no obvious reason to associate them with the seasons; they just seem to be related. The seasonal appearance ofthese constellations, like the changing height of the noonday Sun, provide general signals for the changing of the seasons. For more precise indications of the calendâr we must connect the stars'regular seasonal rycle of appearanies and disappearânces more direct§ with the motions of the Sun. As with the Sun, the most conspicuous seasonal changes of a star's visibitity, its first and last appeârances, happen when the star is near the horizon. Most striking is the first seasonal appeârânce of a star or constellation, known technically as its heliacal rising, which occurs shortly before dawn and is thus, in some way, connected with the Sun. Similarly, the last seasonal appearance of a stâr, the achronical setting, occurs shortly after sunset. With heliacal rising and achronical setting, we have two well-defined astrorromical phenomena that closely connect observations of the stars with the Sun ;rrrd are also sulficiently sharply defined to be suitable for setting the calendar. Unlike the length of daylight, the height of the Sun, or its position on the horizon, which are best observed when they change rapidly in spring or âutumn, thcse phenomena cân provide precise markers throughout the year. The rising or rctting of an appropriate star cân be observed equally well in spring or suûrmer, irr autumn or winter. llut despite the seasonal changes of visibiliry we see that each star, unlike the litrrr, risgs ât the same point on the horizon throughout the year, moving only rlightly in the lifetime of a single person. Here is a constancy, a changelessness, llltt t{r. makes the stars as constânt and unchanging a reference frame as the mountains In the tems of Mircea Eliade, when the celestial - the Sun - touches the earth at the horizon, ofthe world. See Eliade, such a hierophany reveals a sacred space, a sacred time, and the center Sacred and the Profane, pp.20-76; Cosmos and History, pp. rz-zr. I I . The further connection of those stars with the winter hunting season through the role of Orion its hunter suggests the kind of mythologizing by which such associations were presened through tlre generations. on the distant horizon from wllVthieh they emerge and behind which they set. Furthermore, unlike horizon lanc\odnrarksr ths stlrs are Rot confirred to â particular locality; their seasonal risings and[dllsettingr are the sanre over a witie area.'' This relative movement of SurLrurn and stars produces a sharply defined series of days on which stars are first seen. .., These events provide a sequence of benchmarks to define a solar calendar indirectliü ly by observations ofthe stars, rather than directly by observation of the Sun." Of oi course, fromanother perspective, we could say that the Sun is being observed irr,nnndirectly against the framework of the stars. while the Sun and stars provide s: clear paradigms of regulariry, making order of the motions of the Moon and o æf the five planets requires greâter effort. The phases of the Moon recur every 'r rwenty-nine or thirry days, but this period has no simple and obvious connectiorQoon with the annual cycle on which a calendar is based. Nonetheless, since the lunâhââr phases are easily seen, they were widely used to deflne a secondary unit of timorn,e, the lunar month. Twelve such lunar months torlootal some three hundred fifry-four days, about eleven days less than a solar year. ,, Ilthe series of lunar months are to be synchro- nized with the solar year â way fl rnust be found to decide when to insert a thirteenrh month in the calendar. S,lgomé societies ignore this problem by using a purely lunar calendar, and otherr:r:s tolerate a communal ambiguity about .what month it is (scarcely a decision at rrt:all). some decide when to insert an intercalary month by observing the Sun or s: stars to detennine when a particular solar date fell a month "late" in the lunar c calendar, while others define a mathernaticallv *î::,'ryJ'ffi.ïü'îlï'r",î;nsir:s shape or the monthly cycle of phases, \Me can Moon as r2- Strictÿ speaking, the appearances oftlll Moon it goes ,r,.oogr, i* we do the Sun, noting the changing places where it rises bs; and sets or its changing place among the sta$. 'we will soon notice that the Mooh,on'smotionagainst the backdrop of the stars is limited to the same narrow bandr[ of constellations that rise and set near the Sun. Similarly, the Moon rises and setg:üs over the same general range of landrnarks as a.ælso watch the lthe stars are only constânt as the Sun, In both over a band of corutant latitude; they do change r3 as v/e move north orirtolf south. Such obseruations of the stars do noûhotÉeld a true solar calendar, as stellar risings and setdngs recur with the period ofthe sidereal fllyer (365.2564 days). The changes ofthe seasons recur wirh a period ofone tropical year (365.242y4.22 days). The difference is perceptible, adding up to a day in less than â century, and will cause fl: g:roblems to a well-regulated calendar. For most agricultural or ritual concerns, sigrri{icant discreFàrlpflncies will only rise after a number of centuries. Turton and Ruggles, "Agreeing to fl pisagree"; Zeük, "Ethnoastronomy II: Moon '\x/atching"; Neugebauer, IIAMA, pp. 296-297, l:t 3ij3-357, 584-JBj. Theoretically a thirteenth monthsh should be intercalated eyery 2.7rs4 years. Good approxmationstothisperiodarefoundbyirr;jiintercalating3monthsingyears (2.666ù,4monthsinrr yeare (2.7), and 7 months in 19 yearurugs (2.7143). câses, thc Moon follows the sâmc Ëaeneral path âs the Surr, although it does wender north end south of the limits of the Sun's path. At the simplest level, we can view these changing positions as distinctly anal()gous to those of the Sun, with the Moon returning to its former place along the horizon or among the stars every 27.3216 days.'s Note that there is a difference of about 2.2 days between this z7 r / 3-day sidereal month and the common lunar rrronth (the synodic month) of zg r/ z days. This meâns that if the Moon is full wlren it reaches its ârthest north position along the horizon, or a specific place in the constellation Gemini, the next time it reaches that point it will be 2.2 days short of being full, the sixth time it will be 13 days short of being full, which nrakes it a new Moon, and the thirteenth time, which occurs about a year later, it will be a full Moon once again.'o Ilut since the Moon wanders north and south of the Sun's path through the sturs, at a more complex level we cân concern ourselves with these variations of tlre Moon's travels. When does the Moon lie precisely on the Sun's path among 'When does the Moon reach its northern or southern limits? 'Where are thc' stars? 'W'here are they in the heavens? Can they be marked these limits on the horizon? or identified in some way? Is there any regular pattern to these variations? This kind of curiosiry readily leads to several interesting, if not immediately prrlctical, results. Eclipses of the Sun and Moon occur only when the Moon lies r)rr the path that the Sun follows through the stars. If we have concemed ourselves with the paths of the Sun and Moon through the stars, we find that the eclipses oc(;ur ât tr;vo points that move slowly along the Sun's path through the stars over rll.(rr years.'? If we have concerned ourselves with changing places of moonrise lrrcl moonset on the distant horizon, we find that the northernmost and southn'nnlost points that the Moon reaches every zT r/3 days are not fixed, but oscillate b;rtrk and forth around the annual extreme places of sunrise and sunset with the rlrrrc period of r8.6r years." 'l'lre dramatic character of eclipses, and their association with particular points rrroving through the heavens, mây suggest that those points manifest a malign ! fr, We can safely ignore the subde distinction between the sidereal month, measured against the stars (27.32166 dâys at A.D. 5oo), and the tropical month, measured from the vernal equinox (27.32r58 dâys ât A.D. 5oo). The accumulated difference of one day in a millenium would have little impact on practical astronomical obseroations and calculations. 'l'he Moon is fuil at its northernmost position at what is called the mid-winter full Moon, the full Moon of the winter solstice. The new Moon that appeare at this same northem extreme six or seven sidereal months later is the mid-sumer new Moon. Similar eclipses in the same constellation mst be separâted by an integral number of years. The rrearest integral value, nineteen years, is also a Metonic cycle which reconciles the iunar and solar calendars. The Babylonians, for one, were clearly aware thât similar lunar eclipses, or their irvoidmce, recumed at the sme position among the stars every nineteen years. Cuneiôm Text, llritish Museum 4roo4, rev. r8-r9; as cited in Moesgaard, "Full Moon Serpent," p. 5r. Ibom. Megalithir Sîtes in Birain. pp. zo-zj. power to obscure the two great luminâries, It would take a somewhat Efeâter level of abstraction to connect the ever-changing positions of extreme moonrise with eclipses and to grant a po\À/er to those landmarks. In some cultures, however, these vagaries of the inconstant Moon have been dismissed as irrational. To summarize the range of possible lunar observations, we can observe the phases of the Moon or its position among the stars or on the horizon to establish a kind of auxiliary calendar. Among these options, it seems unnecessarily complex to relate the Moon with stars or horizon, rathsr than simply observe the Moon itself, In either case, such simple observations cbuld lead to the further calendric problem of relating the solar y.r. to the lunar ,]rrorrth. Finally, long-term observations of the changing position of the Moon can point the way towards an undentanding of eclipses. Observations of the complex morions of thg Moon and five planets among the stars or on the horizon, while significânt to the development of theoretical astronomy and astrology, had little meaning for those astronomies concemed with the reckoning of time or the keeping.ôf the calendar." Their principal contribution to practical âstronomy was in the sense of which Ptolemy spoke. Insoâr as mathematical astronomers had demonstrated that the apparently erratic motions of the planets were subject to mathematical laws, this achievement extended the be]ief in the "constancy, order, syrnmetry and calm" of the celesrial regions, an order that could be used to govern human âctivities. 19. For a detailed treatment of earÿ theoretical astronomy, see Neugebauer, HAMA. CHAPTER TWO The heritage of astronomical practice 'When - Zeus willing * counting from the winter solstice sixty days have passed, then the star Arcturus leaves the sacred stream of Okeanos and fint rises brilliant at eventide, then the swallow, shrill voiced daughter of Pandion, flies up into the light when the new spring begins; it is best to prune your vines before her arrival. Hesiod, Works and Days (ca. VIII c. n.c')' ln his Works and Days, Hesiod touches here on many of the'rnethods and functions of early timekeeping: counting the passage of days, watching the Sun, stars, lnd birds for signs, and preserving a judicious concern for the gods and one's crops. Simple practices like these form an important part of the background to early medieval astronomies, yet the nature of their connection remains uncertain. ln many cases lve can establish direct connections befween ântique traditions and the Middle Ages; in others we can only point out the prior existence of these ideas and practices and ask whether, and to what extent, they influenced analogous elements of medieval astronomies. Prehistoric solar horizon calendars rl, 'l'he earliest part of the astronomical heritage of the earÿ Middle Ages is not Irrrnounced with the eloquence of a Hesiod; it lies concealed in the crude stone lnonuments erected in the British Isles during the period from 4ooo to Iooo s.C.' Most farniliar of these megal-ithic strucnrres, that is, structures made of large, roughly hewn, stone blocks, is Stonehenge. Almost everyone has heard, and most cxperts accept, that the axis of Stonehenge points towards the place where the Hesiod, }{/or&s and Days, s6q-s7o. The seminal studies of British archaeoastronomy are the writings of Alexander Thom; on his work and its signitcance see Ruggles, Records in Stone. The best introduction to the issues in megalithic âstronomy remains Heggie, Megalithic II Science. tLxtlilnir Sun rises et the summer solstice.r tn additior, a rânge of further, more eoRtrovenial, alignments involving other extreme points of sunrise, sunsêt, moonrise, and moonset have been proposed (Fig. r). Although Stonehenge is the most âmous megalithic structure at which such astronomical alignments have been noted, it is not the onJy one. But the question of whether these orientations were deliberflte or merely fortuitous called forth aunrh H.al Stotll Northammoal mfflr careful consideration of the signiûcance of V'arious forms of evidence. stonehenge and other megalithic structures share the-i ambiguity of most archaeological remains; the possible interpretarions thar we can assign to them are limited only by our imagination. Selecting which of /iese possible interpretations reflect actual functions served by these structures.éalls for a greater degree of restraint. The solar alignments immediately suggested that they marked solar observarions for regulating the calendar. Earÿ invesrigators nored that these alignments pointed to the same division of the year at the solstices, the equinoxes, and dates midway between them that were indicated by ôlklore and traditional calendars.a The subsequent studies of Alexander Thom went beyond the examination of individual structures to investigate possible alignments ât large numbers of sites. Thom's studies found evidence for the same basic calendric framework and claimed further indications of subdivisions of the year into as many as thirry-rwo equal partsi and evidence for extremely precise solar and lunar observations.u Critical examinations of this evidence and new, more systematic surveys of carefully defined groups of sites have led to rejecrion of the more extreme of these claims. The evidence for highly precise "sciendfic" observations is generally dismissed âs the product of various kinds of unconscious selection of data. What remains from these more critical analyses is evidence for low-precision calendric observations of sunrise and sunset to mark the divisions of the year into eight equal parts and evidence for similar low-precision observations of the rising and setting of the Moon, perhaps associated with religious rituals.' Hawkins and.\ÿhite, N\ ;N lloathrrnmost lioonrl =§T't'---,(=-\L E Eo r r -'t- taffi 7r,Ir*"1 -+ tz- -/ mnæl 7. zr-23, 4o-4r, t7B-tgo, 203-2cr6, and passim; Someroil1e, "Prehistoric Sitcs in Brittin, pp. ro2, ro7*tr7. Ân inportant characteristic of Thom's analysis is that he proposed that the Sun's motions diüded the yeâr into equal units of time, rather than obsewing those motions against equal angular divisions of the zodiac. This equal-time model is more plausible, as it does not require the production of measuring instruments and development of geometrical concepts on which the equal-mgle model is based. These two models lead to diferent partitions ofthe year and different rising points ofthe Sun on the horizon. Thom, Megalithic Lunar Obseoatories; Thom ând Thom, "Megalithic Lunar Lines." These claims for highly precise estronomy suggested to some a centralized society dominated by a highly skilled eüte of astronomer priests. MacKie, Science and Society in Prehistoric Britain. This view was at odds with the accepted picture ofBritish prehistory and can no longer be supported by the evidence of low precision astronomical alignmentsHeggSe, Megalithfu Sdence, pp. 165, r8r, 222-223; Moir, "Objections to Scientific Astronomy ir Prehistory." " T"È -ini§ mlnlmum I o .":L ti; Nonhom ,a,,,ili,,ii;,ii:,ffi:uuo Stonehenge Decoded. Even skeptics Stonehenge, pp. Monuments." Thom, Megalithic I ---)Q".,*^ ç§ z/ now acknowledge the solstitial alignment ofthe avenue extending from Stonehenge; Âtkinson, "Archaeoastronomy ofStonehenge." Loc§er, I | ro | 20 I 30 I 40 I 50 l, 6d I 70 MoteB r. Claimed astronomical alignments at Stonehenge. The alignments are supqimposed on a plan of Stonehenge I (ca. 3roo a.c.). Recent excavations have revealed the imprint of a second stone immediately to the left of the Heel Stone, framing summer solstice sunrise betvveen the wvo. The familiar circle and honeshoe of larger sarsen stones were constructed about 2ooo B.c. Reprinted from O. Gingerich, "The Basic Astronomy of StoneFigure henge," by permission. More recent studies have revealed the clivcniry of astronomics pmeticed ât carefully defined and geographically limited groups of sires. I\ugglest stucly of 'rvestern scottish sites showed statistically significant evidence of alfnments to the rising and setting Moon at its southern extreme but only slightly more solar calendric alignments than expected and not enough to be siatisti*cally significant.u A different pattern emerged from Burl's examination of a cluster of large stone circles in wales, southwest Scotland, and Ireland. Burl found little evidence for lunar alignments but â greater than expected number of arignments marking sunrise on the dates dividing thg solar year into eight equal parts. Archaeological evidence, including trade goods such as stone axes, proüded a context ôr this âstronomy by suggesting that these stone circles may have been sites of ceremonial and trading assemblies, for which the solar calendar determined the time.e In summary, these studies of megalithic alignments indicate that the prehistoric peoples of Britain had a tradition of observing the Sun and the Moon. They kept a solar calendar dividing the year into eight equal parts, and performed the kind of lunar observations that could lead logically, but not necessarily, to âtrempts ro reconcile the morions of the Sun and the Moon. In some respects "megalithic" astronomy does not fit the simple model of an agricultural calendar. Lunar observations are only imperGctly related to the passage of the seasons and seem more related to lunar rituals than to the keeping of a calendar. The solar alignments indicate equal arrificial divisions of the year rather than the irregularÿ spaced, natural times of agricultural activities. The archaeological evidence for ceremonial and trading assemblies at sites where astronomical alignments marked these regular divisions of the year suggests a more complex interaction of astronomy, socieÿ, ritual, and trade than that of a simple farmers' calendar. As we will see, certain elements of the solar calendar established by ,.megaobservers of the heavens survived into the early Middle Ages, deqpite the cultural changes brought about by successive incursions of celts, Romans, and Anglo-Saxons. To the extent that we find the same solar calendar playing similar lithic" i social roles in changing cultural contexts, \À/e can begin to understand how survivals of prehisroric astronomical traditions influenced early medieval knowledge of the heavens. Classical horizon systems The prehistoric Britons were not the only early Europeans to define a system of orientation in terms of the changing position of the Sun along the horizon. Similar 8. 9. iystê$rs were eonmonly ured in Greeee and Ropre, Antique writen Gonvention= rranred thc winds in terms of the rising and retting points of the Sun at the dly rohtiees and eguinoxcs, plur north and south, rather than naûring directionr defined by an equal geometric division of the horizon.'o The original system of eight named winds based on observation of the rising tnd setting Sun has significant limitations. The places where the Sun rises at the rclrtices do not fall at northeast or southeast, but only about a third of the way flonr equinoctial sunrise towards due north or south. The large gaps berween the tolËtitiâl directions and north or south were often filled in by four additional eiirections. This system was embodied in a twelve-sided tower of the winds €rected ât Rome, differing from the octagonal tower of the winds in Athens," Although dominant, these were not the only direction systems in the Roman trnrlition; ât one point Vitruvius showed how to construct an octegonal wind rose witlr only eight equally spaced winds insteâd of winds based on sunrise and set âi tlte solstices and equinoxes." 'l'hrough late antiquity and into the Middle Ages these directional winds, and thsir relationships to the rising and setting Sun, continued to provide architects witlr a guide for orienting homes and estates," scholars with a framework for geographical and cosmiç orientation," and artists with ornamental motifr for morait's lnd other decorative art. The stellar calendars of antiquity lf'the morions of the Sun provided one way to mark the turnings of the year, rhe literary sources found in medieval libraries more commonly described calerrtl:rrs based on the risings and settings of the stars. Although it was not known irr the Middle Ages, the archerype of later stellar calendars is found inthe Worles Days of the Greek poet Hesiod, quoted at the head of this chapter. Hesiod 'ud tnixes folklore of planting crops, caring for animals, and treating diseases by the phases of the Moon with advice that the Pleiades define the proper times for pkrwing and reaping, whether one lives on the plain, by the sea, or amid a forest.'r llcre Hesiod alludes to a major advantage of a stellar over a horizon calendar: the r'onstellations provide celestial benchmarks that, once known, can be used over I wide area without having to identify new local landmarks everywhere one goes. llecaÉse of this univenality, stellar calendan were widely employed and dis- ro. r. rl. Ruggles et a1., Megalithic Astronomy, fig. rz.r, cf. p. 13. 3o7. Burl limited his study to twelve stone circles having dimeters greater than Circles of Cumb.i"," pp. rg7-rgï. 30 meters. Burl, ..Stone t4. s. r Pliny, Hkt. ndt., 2-46-119; Seneca, Qraest. nat., 5-r6i Vitruvius, De architertura, r-6-4-5. Pltny, Hist. nat., zi6.rrgi Cetus Faventinus, De architectonicae, z; Noble and Price, "Tower of the Winds." Vitruvius, De archittctura, 1.6.12-13. Vitruüus, De architectura, 6.4, 6.6. Destombes, Mappemoniles, pp.28, 35-36; Obrist, "Wind Diagrams." Hesiod, Works and Days,384-390, 564-624, 765-824. by mâny RomÀn wrlterï, wlio emulated Greek modcle in thil ra in other .nly to sample The poet virgil (7o19 n.c.) wrore his Georgies as a guide for fanners, and like Hesiod in his works and Days, included weather rore and traditionar beliefi about the suitability of phases of the Moon for certain tasks. yet he went beyond Hesiod in astronomical detail to proüde a brief discussion of the narure of ihe celestial sphere and how the sun's pâssage along its slanting path is marked by the twelve ànstellations of eu§§ed than had hir predeeeaeon, He did not limit himself to prâetical obrervations deter,mine tbe timcs to plant and harvcst, but noted how calendars connect ehanglng coune of the seasons to thc motion of the Sun and connect thât in turn, to the disappearances and reappearances of the stars. Bedtles explaining the general principles underlying the stellar calendar, Pliny his way systematically through the year, discussing in turn the activities for by the rising and setting of each celestial sign. 'Where Hesiod and Virgil areas. This is not the place to consider all auch preientatioRs, but a few that were read and quoted in trru inJy rtaiddre Ages,'n llr, the zodiac.'7 But such knowledge is not enough; vi.grt cautioned the farmer to watch the planets and wonhip the gods. A man is blÀsed'both when he knows the causes of things and when he knows the rustic gods.,* The gods are central to anorher stellar calendar known to the early Middle Ages: The poet ovid (43 o.c.-ca. a.o. rg) did not direct his Fasti to the practical needs of farmen, but addressed ceremonial concerns by marking the stellar signs of civic and religious festivals and describing the gods arrd .rr..rt, the feasts com_ memorated, all within the framework of Julius caesar's reformed calendar. In subject, the Fasti is much more ân âccount of Roman mythology and history than it is an astronomical treatise. yet in structure rhe Fa.sti is a"calendar, and ovid mentioned in their tum the seasonal risings and settings of the stars, the changing of the seasons, and the solstices and equinoxes. As such, the Fasti provided another vehicle for the transmission of these astronomical elements of the Roman calendar to the Middle Ages. Much broader in scope is the Natural History of pliny the Elder (t.». z3_79). Like later medieval wrirers, pliny did not treat astronomy as a single subject, but discussed vario,s aspects of what rffe see as a single subject in diherent sections of his book. Book Two treats cosmology, discussing the nature of the univene, the motion of the stars, sun, Moon, and otherplroet, the sphericiry of the earth, and related topics. Book_Six deals with geographical issues, Àr.rrrrirrg the size and shape of the earth and the parallels of ratitude and noring the chanfi.rg durarion of the longest day and the changing length of the .roôrtime shadori as" ore goes north of the equator. Book Eighteen considers the basis of the calendar within a general discussion of agricultural practices, in much the same fashion as we have seen in the Georgics but surpassing Virgll in detail.,, Here Pliny related âstronomy to human needs, praising Hesiod, virgir, and others who had led in this arduous task of "introducing thJdirri.r. science of the heavens to the ignorance of the rustic."'o In his discussion of the agricultural calendar, Pliny presented a much more detailed exposition of the calenàric probr6. 17. r8. I9. 20. Ogflvy, Books Kaown to the Englkh; Laistner, Thought and lttters, pp. zr}_22o. YirgSl, Georgics, r. zo4-z 58. Y irg;L, Ceorgics, r. 4z 4- 46 4, 27 7-286, 3 3 J-3 jo; 18.56.2c,6. given single dates for these phenomena, Pliny deliberately presented conflictfiom a wide range of sources: d,rta rrrorning setting of the Pleiades is given by Hesiod . . . as taking place at the close the auturnnal equinox, whereas Thales puts it on the z5th day after the equinox, Anaxt$tcn(ler on the 4oth, Euctmeon on the 44th, and Eudoxus on the 48th. We follow the Ebrervation of Caesar especially: this will be the formula for Italy: but we also state the ldewr of others, since we are not treating of a single country but of the whole of nature." §lhe âË Plitry accepted these differences as due to the di{Ierent regions for which the 6blervrtions were made. Although he knew in general terms that the times of thene phenomenâ may vary frorn place to place due to the convexity of the tlrliverse and the sphericity of the earth, he avoided the mathematical details rctluired to reconcile or criticize these conflicting dates." This lack of critical judgernent among competing sources, characteristic of Pliny and his fellow eneyclopedists, coupled with the waning knowledge of the geometrical basis of flttcietrt âstronomy, challenged Pliny's medieval readers as much as it enlightened thenr. Geornetrical astronomy Itlirry's treatments of âstronomy v/ere not limited to calendric materials. He introtJuced a wide range of less immediately useful astronomical concepts. FIe rlistinguished berween stars and planets and discussed in vague terms the charactcristics and periods of their motions and gave various estimates of their distances li'om the earth. He described the retrograde morions of the five planets and even sttggested a physical explanation of these retrograde motions in terms of rays crrtanating from tHe Sun." FIe explained that eclipses of the Moon are caused by 2t. .rr. 2. 4g(F4g 4. On Pliny's astronomy and its influence, see Bont, plinius und seine ltset; O. ped.ersen, ..Astro_ nomical Topics in Pliny," esp. pp. r68-17o; and Eastwood, ..plinian Asrronomy.,. Pliny, Hlst. nat., bg rt. Pliny, Hist. nat., 18.57.2t2-t4. Pbny, Hist. ndt., 18.57.2to, z161; 18.59.zzo-zzz.Pliny never goes beyond a rudimentary discussion of the underÿing principles to âttempt geometric demonstrations of how the spherical shape of the earth influences the risings of stars. Pliny, Hist. nat., 2.6-20. The notion that the Sun's râys cause the retrograde motion of the superior plânets is an âttempt to explain the easily observed fact that these planets do revene their motion when they are opposite the Sun. lli the earth's shadow and that they recur with a periodie cyele of :r3 monthË,tr He noted that all seven planets, including the Sun, travel in the band of the zodiac, moving north or south of the center, and that the zodiac is inclined, although he failed to define it or its inclination in reference to eny geometric system of coordinates. He gave the places in the zodiac of rwo different values of the planets' apsides altissimae, one described as the greatest distance of a planet's circle from the center of the earth, the other as its greatest elevation from its own center." Yet he did not clarify the meaning of these rwo dif[erent concepts, the first of which is related to the eccentricity of the planet's deferent in a geometric model and the second of which is actually the planet's exaltarion, the place where it has the greatest astrological influence. Furthermore, he did not relate rhese to any geometrical model, except to note that the planets âppear to be smaller and to move more slowly when ârther from the earth. It was such rudimentary under* standing of the terminology and findings, of Greek geometrical astronomy, but not of its methods and principles, that Pliny passed on to succeeding generarions. If we are to understand the limits of early medieval âstronomy, we must recognize not only what medieval astronomers leamed from their predecessors, ttut what they lost. The foundation stone of ancient astronomy was a geometrical model of the universe in which the stars were viewed as cosmic ornaments on â sphere that rotâtes around the central earth (Fig. z). Greek âstronomers, like most others, began by placing the observer in a privileged posirion at the center of the universe.'u But by choosing the stars rather than a local horizon âs their reference, Greek astronomers not only framed a universally applicable âstronomy, they also laid the groundwork for mathematical analyses that would be impossible in an âstronomy ried to the horizon. The primary achievement of this spherical model was that it explained the simple observâtion that most stars rise and set each day at the same points on the eastern and western horizon, while some wheel around in the northern s§ without setting. For traveling merchants and explorers like the Greeks, this model also explained that as one travels northward on a spherical earth, some stars sink lower in the southern sky until they never rise above the horizon, whereas as one travels south, some stars that cannot be seen from Greece begin to peek above the southem horizon. The stars betvveen the never*setting northern stars and the 24. Pliny, Hlst. nat.,2.ro.56-7.This so-called Saros cycle of zzj rymodic months (approximately 18 yean) is more precise than the approximate "rycle" in which ecüpses sometimes recur at the sme point among the stars after nineteen yetrs (245 slmodic months). Eclipses sepârated by a Saros rycie, however, have moved by some ten degrees among the stan or, what is roughly equivalent, by some ten days in the year. 25. Phny, Hkt. nat., 2.13.63-65. Neugebauer, HAMA, pp. 8o2-8o3, finds only vague oudines ofa planetary theory in Pliny. 26. On the mmifold poütical, philosophical, and mythic signiûcances of the center in Greek thought, Vemant, The Oigins oJ Greek Thought, crans. of lts origines de la pensée grecque (London: Methuen, r98z), pp. lgrr32. see Jean-Pierre Pigarc z. The Greek model of the universe. In this model the sphere ofstars rotates daily around the central earth. For an observer at O, stârs north ofthe circle CNC will never set, stars south of the circle ISI will never rise and cannot be seen, and stars between CNC and ISI will rise at fixed points on the eastern hoçizon NES and set at fixed points on the westem horizon Str'llN. Reprinted by permission of the publishen from The Copemican Reuolution: Planetary Astronomy in the Deuelolment oJWestem Thougÿtby Thomas S. Kuhn, Cambridge Mass.: Harvard University Pres, Copyright @ tg57 by the President and Fellows of Harvard College, @ r98S by Thomas S. Kuhn. never-rising sourhcrn stars are aboie ihe horizon decreasing from north to south. The spherical model connects our observations 'liii, for varying period; of time, of the sun and the stars by considering that the sun moves through the stars on an inclined path traced on the celestial sphere. This path, called the ecliptic, goes through those twelve constellations making up the zodiac, which rise and set near the Sun. when the sun is in the northem portions of the ecliptic it rises in the northeast, passes high overhead ât noon, sets in the northwest, and - like the northem stars shines for more than twelve hours. Conversely, when the Sun is at the southern portions of the ecliptic it rises in the southeast, is low in the noontime sky, sets in the south\À/est, and shines for Gwer than rwelve hours. The Sun traverses the ecliptic once a year, moving in a direction opposite to the daily rising and setting of the starry sphere..Thus the Sun lags behinà the srars by about four minutes per day, or looked at another way, the stars move ahead of the sun by about four minutes perday. This model, then, provides an explanation for the heliacal rising of a star when it emerges from the dawn glare of the sun and rises before dawn four minutes earlier on subsequent days. Furthermore, since the sun's travels along the inclined path of the ecliptic take it north and south to produce the changes of the seasons, this model explains why the heliacal rising of a parriculâr star is tied to a particular date in the solar year. Many of the qualitative explanations of the principal asrronomical phenomena provided by the spherical model continued to be taught through laie anriquiry and the early Middle Ages. But geometry is not merely qualitative. Greek astronomers had used this simple spherical model to compute how long a given star, or the Sun at a given point on the ecliptic, would be above the horizon. More complex geometrical models were rnabyzed to yield numerical ans\Mers to other, more subtle questions about the motion of the Sun, Moon, and other planets. These trigonomerric techniques exceeded the mathematical skills of medieval scholars. Planet Equant Deferent Center Earth Figure 3. Ptolemy's epicyclic model. This model applies to Venus, Mars, Jupiter, and Satum; more complex models are required for the Moon and Mercury; simpler epiryclic or eccentric models can be used for the Sun. but is most commonly known by the Larin transliteration of its Arabic title, the fict that for a long time this work was lost to the Latins, who rediscovered it in the Islamic world only in the rwelfth century. 'lhe Almagest is a selÊcontained treatise on mâthematical astronomy, drawing on a discussion of the instruments needed to observe the positions of the stars, and Almagest. This reflects the historical Ptolemaic astronomy The greatest of the computational achievements of the ancient âstronomers rvvas the system of claudius Ptolemy (ca. roo-ca. r75). His work was so complere that he eclipsed his predecessors, and, as Neugebauer notes, he had no worthy successor. FIis work continued to provide the basis for a tradition of mathematical astronomy in the Byzantine and Islamic worlds, but in the Latin'west he remained little more than a name, often confused with the ptolemaic rulen of Egypt and sryled Ptolemy, king of Alexandia.', Ptolemy's chief astronomical work is titled in Greek the "Megalé Syntaxis,, 27. Isidore of Seville, Etymologiae,3.z6; Neugebauer, I:MMA, p. 5. to trigonometry and spherical astronomy to develop geometrical rnodels for the motion ofithe stars, Sun, Moon, and other planets based on selected astronomical observations extending back some nine hundred years. In an introduction these models each planet is carried around on a circle called an epicycle, which in tum is carried around on a larger circle called the deferent (Fig. :). Ptolemy used these models to prepare tables for a wide range of astronomical computâtions." 2ll. For a mathematical and historical commentary, see O. Pedersen , A Suney of the Almagest. The With the Almagest one can compute the positions of the stân, Sun, Moon, and other planets for any given tinre; the tinre of the solstices and equinoxes arrcj when the Sun enters each sign of the zodiac; the time and characteristics of eclipses of the sun and Moon; the time of the appearances and disappearances, of the stah; the time of the greatest elongation of Mercury and venus from the Sun as morning and evening stan; and the time of the appearance, disappearaîce, and direct and retrograde motions of the five planets. Besides detailing the methods and theoretical bases for such computations, the Almagest also includes such practical data as Ptolemy's values for the length of the year, the lunar month, and the seasons." Ptolemy did not complere his work in mathematical asrronomy wirh the Alrn his later Planetary Hypotheses Ptolemy developed a physical realization of this mathematical model by a system of solid spherical shells, which contained a planet and additional spherical bodies representing its deferent and epicycle (Fig. 4). Since the inner ând outer surfaôes of these spherical shells were concentric with the earth, Ptolemy could nest them in the order Moon, Mercury, Venus, Sun, Mars, Jupiter, and satum to arrive at a cosmos of concentric spherical shells whose outermost dimension was 19,865 times the radius of the eârth.ro lHis Handy Tables consoltdated and expanded the Almagest's tables and presenred them in convenient form with instructions for their use in astronomical computations, but without the Almagest's geometrical models and demonstrations. Although ptolemy also wrote lesser works on astronomy, on astrology, and on astronomical instruments, the Almagest, the Planetary Hypotheses, and the Handy Tables define the core of Ptolemaic astronomy. If we are to understand the later transmission of ptolemy's astronomy, .we should distinguish several levels at which someone could be said to "know" Ptolemaic âstronomy. At the simplest level one might know a few astronomical ideas culled, perhaps ât second hand, from Ptolemy's works. At an internediate level one might be able to use some or all of ptolemy's tables to perform certain astronornical computations , a practical manipularion of numbers that requires little understânding of geometrical astronomy. conversely, one might know the strucmagest. 29. eariiest obseroation used of 19 March, 7zr n.c. - jo. by Ptolemy is of a lunar eclipse observed at Babylon on the evening r Following Hipparchus (fl. ca. 16z-rz7 r.c.), ptolemy computed the tropical year as /a 365 %* days 365;r4,48d 365.246667d and the length of the rynodic month as approximately z9;3 r,5o,o8,zod = 2g.53o594r 40. He gives the interoâls ftom vernal equinox to suÀmer solstice as 94/, days, sumer solstice to autumal equinox as gz/. days, autumal equinox to winter solstice as 88% days, and winter solstice to vernal equinox as 9o% days. ptolemy, Almagest 3.r, 4.2,3.4. The Arabit version of Ptolemy's Planetary Hypothesis, Book I, part 2.3, ed. and râns. B. R. Goldstein, Transactions oJ the Amuican Philosophical society, vol. s7, pt. 4 (philadelphia, 1967), p.7; : Figure 4. Ptolemy's physical planetary model. Compare this physical realization with the mathematical model of Figure 3. Since the inner and outer surfaces are concentric, adjacent planetary models can be nested with no intervening empty space. : Murschel, "Ptolemy's Physical Hypotheses." ture of the Ptolemaic model in which planets are carried around on epicycles which in turn âre carried aroggd on deferents (Fiæ. : and 4) without being able t«r perform any astronomical computations. Àt the highest level one could know lll the details and dimensions of these.planetary models, know how to use âstrorromical instruments to make the observations needed to derive the mathematical pàrameters of Ptolemy's models, and know how to use these models to compute rrstronomical tables of the sort that Ptolemy provides. Someone at any of these lcvels might be called a follower of Ptolemy, but late antique scholars had reached only the lower levels. They eould ,rot pam on the full ptolemeie 6adltiop ro rheir §uccessors; ât n10st they could pique their §ucce§§

Author Stephen C. McCluskey Isbn 978-0521778527 File size 148.9MB Year 2000 Pages 252 Language Englisch File format PDF Category Astronomy Book Description: FacebookTwitterGoogle+TumblrDiggMySpaceShare Historians have long recognized that the rebirth of science in twelfth-century Europe flowed from a search for ancient scientific texts. But this search presupposes knowledge and interest; we only seek what we know to be valuable. The emergence of scholarly interest after centuries of apparent stagnation seems paradoxical. This book resolves that seeming contradiction by describing four active traditions of early medieval astronomy: one divided the year by observing the Sun; another computed the date of Easter Full Moon; the third determined the time for monastic prayers by watching the course of the stars; and the classical tradition of geometrical astronomy provided a framework for the cosmos. Most of these astronomies were practical; they sustained the communities in which they flourished and reflected and reinforced the values of those communities. These astronomical traditions motivated the search for ancient learning that led to the Scientific Renaissance of the twelfth century.     Download (148.9MB) The Decade of Discovery in Astronomy and Astrophysics Precession, Nutation And Wobble Of The Earth Kepler’s Geometrical Cosmology Beyond the Stars: Our Origins and the Search for Life in the Universe Civilized Life in the Universe: Scientists on Intelligent Extraterrestrials Load more posts

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