Astronomy

Bootes, the Herdsman in a 9th-century A.D. Aratea. picture courtesy St. Gallen, Stiftsbibliothek, Cod. Sang. 902, p. 85, e-codices, Vitual Manuscript Library of Switzerland

Astronomy had declined by the end of the Roman empire as elites moslty worried about skills for politics and warfare. The Church, as far as it is concerned, had had soon a interest in practical astronomy as Christians needed to correctly determine their main festivals along each year. As they first tried to have match the Jewish, lunar-based and the Roman, solar-based calendars, clerics, due to the harshness of such a task, eventually opted for the Roman Julian calendar, since with it, many religious holidays could be given fixed dates which were independent of the celestial events. The birth of Jesus Christ and John the Baptist were linked to the solstices of winter and summer respectively as Easter had to be determined each year, being linked to a full Moon. The monks, on the other hand, were too involved in a number of feasts and ceremonies and they had further to keep a record of time for their prayers. Star watching or some basic candle-clock was their only mean to nocturnal timekeeping. Water clocks would come by the 10th century only. The Church arithmetical technique of calculating Christian festivals was named the 'computus', from Latin 'computare', for 'to calculate' as in the Anglo-Saxon world, the technique is often termed 'calendar reckoning'

In the Early Middle Ages, on the other hand, clerics and monks kept a interest in science beyond those need of calendar reckoning and they kept studying maths and astronomy. Science then was mostly known through some Latin sources. Four sources, before the Carolingian era, were how astronomy was transmitted, namely Calcidius' commentary on Plato's Timaeus, Macrobius' Commentary on the Dream of Scipio, Martianus Capella's "Marriage of Philology and Mercury", and Pliny's Natural History. It's possible too that some translations of Ptolemy by Boethius to have existed

What Sources did Carolingian Scholar Had a Their Disposal in Astronomy?

Astronomy, by the Carolingian times, kept to be teached in the cathedral and monastic schools as they further had science like a part of the cursus. It was almost arithmetics and plane geometry which could form a basis for any astronomical interest. About 135,000 works in Latin were dedicated to calendar reckoning with tables of data and essays allowing to compute the Easter date for the current year and coming ones! Clerics and pupils still had books of maths and plane geometry at disposal. First, they commented Victorius of Aquitaine's Calculus, or a book about arithmetics. Then Boethius' 'De arithmeticae institutione libri duo' during the 9th century, with too Euclide's Elements VII, VIII et IX, which are the books of Euclide about arithmetics and what was premium in the matter at the time. Some of the problems submitted to the pupils' sagacity are still in use today, in maths and algebra, in schools in the Anglo-Saxon world. Some other works include the 'Calculatio Albini magistri', Propositiones ad acuendos iuvenes, De arithmeticus propositionibus, or the 'Altercatio duorum geometricarum'. Plane geometry was adressed through Euclides first four Elements and other numerous texts as that domain was of interest, allowing for land surveyors and engineering. As far as astronomy proper was concerned, most of main Greek astronomers works had not been translated into Latin at the exception of some, or some brief abstracts. Eudoxios (408-355 B.C.), which further had been complicated by Kallippos (370-300 B.C.), or Aristotles (384-322 B.C.) were few known. Had disappeared too the brilliant works of Apollonios (262-190 B.C.) and Hipparchos (190-120 B.C.) except what Ptolemaios (100-165 A.D.) had kept. Hence astronomy, at that time, had come to be known as purely descriptive as the Latin texts by which it was known, offered no explanation of the methods by which such information had been originally assembled. Such work like those of Ptolemy and the other Greeks had been lost to the poetic and philosophical astronomy of Aratus or Plato. Isidore of Seville works also were available. Martianus Capella's textbook about the liberal arts, which was widely available, presented in its astronomy section a model of the solar system based on ancient Greek sources. It had Mercury and Venus orbiting the Sun, as the Moon, the Sun, and the other planets were orbiting Earth. Plinius' 'Natural history' was known too. Louis the Pious commissioned at least one superb astronomical manuscript, the famed Leiden Aratea or Aratus. This manuscript was written maybe about 816 A.D. from the Germanicus' Latin translation of the "Phaenomena", the oldest Greek sky guide, written by Aratus of Soli in the 3rd century B.C. It was prepared either for Louis the Pious about 830-840 A.D. in Aachen or in Ingelheim at the court of Impress Judith, where Louis himself came to settle. Alcuin, on the other hand, wrote several astronomical treatises. Generally Church had developed a preference, for Plato as its system was a geocentric one

What Were the Theoretical Knowledge and Astronomical Tools by The Carolingian Times?

This was the state of astronomy at the time of Charlemagne. The endeavour to train more learned clerics, the interest of Charlemagne himself as an amateur astronomer who took lessons from Alcuin then Dungal, or the possible idea that the Carolingians had of the cosmic and natural order as linked to their duty of governing the earthly kingdom in the perspective of the heavenly one, all this led to a revival of astronomy. The Carolingian renaissance allowed some conceptual, technical and computing renewal as the Carolingian scholars really developed science perspectives allowing for theoretical and practical advances. As the Frankish teachers used Aristotles few only, nor they read Ptolemaios, they did not stopped at points of views which would have been taken from the sole Scripture

Practically, this effort first took the form of some improvements brought to computus. Astronomical and computistical anthologies emerged around 809 after that an astronomical computistical conference was held at Aachen this very year. Such works added to the traditional computistical texts, including solar phenomena, weather, computational tables, and descriptions of the structure of the heavens and catalogues of stars and the constellations. Such works were, most of the time, accompanied with illustrations. Then Carolingian scholars too advanced in astronomy

As far as theoretical reflexion about our solar system is concerned, they did ignore Ptolemaios 'Megale Syntaxis', which came later to be named the 'Almageste', who had summarize the epicycle system of the Greeks which consisted of one additional circle located on a main one figuring the orbit of a planet, and allowing for a explanation of the yearly apparent motion of planets against the starry background. Main circles were centerd upon the Earth. Carolingian scholars however had still at their disposal another, Aristotelician model of concentric, embedded circles around the Earth under the form of a diagram and, too another, Pythagoricain model of the solar system with the relative distances between planets' orbits under the form of the harmonic, or tonic intervals. Both models were the basic way to visualized the series of the planets in our solar system as scholars used those like a base to study the varied places a planet had on its orbit and the intervals between such places. Following Martianus Capella further, they had choosen too that Mercury and Venus were orbiting the Sun with the Sun and the other planets orbiting the Earth

As far as the tools used by scholars interested in astronomy are concerned, a remarkable feat is that they did not have at disposal any telescope allowing to improve their observations

• the basic, useful tool of the time was a neat concept of the Zodiac, that fictional line in the sky the Sun looks like journeying along in the course of one year. Zodiac was a standard science tool, with its twelve signa, the divisions of which parted between a reference -'puncti' or points- in longitude and 'partes', or 'parts', in latitude
• the Aratus was another tool as it figured the zodiacal signa and constellations under the form of celestial figures taken from the Hellenistic myths. The Aratus allowed a user to remember the positions of stars in the sky. The Aratus eventually was a sort of planetarium. Two other such stereographic, two-perspectived, celestial planispheres, of a more common use that the Aratus in use at the court, were used in the Carolingian schools, a one found in the St-Emmeram school in Regensburg, another in Fulda as the other monastic schools in the Empire had them copied from the 9th to the 12th century A.D. and were pretty accurate! According to a tradition which was to remain that of the Middle Ages, constellations in the Aratea are depicted like they would be seen from the outside of the celestial sphere. Leo, the Lion thus, for example, has its head in direction of the East
• By the beginning of the 8th century A.D., the Venerable Bede, in England, was using a 'horologium in terra', a ground-laid and night-used astronomical tool, with a great circle marking the Zodiac reference. Albeit still not well understood that tool had allow Bede to efficiently forecast the tides, in relation to the lunar cycle to the point that his theory still is at the base of the British Admiralty Tide Tables today. That likely translated into other such instruments used to check the position of stars or planets in a accurate way. One knows, for example, that a 'horologium nocturnum' was in use in the St-Peter school in Salzburg and the St-Emmeram one in Regensburg as mentioned by two manuscripts about 812-816 A.D. Such a aiming instruments featured several mobile plates above one each other. Each plate features drawings and points' sets as they allowed to coordinate the yearly 12 months-365 days with the 360 points of zodiacal longitude. Another plate allows to coordinate the positions of the Moon with the starry background along a 28-day lunar cycle. Another match allowed to coordinate 24 solar days along a whole of 16 lunar cycles, likely used to forecast eclipses. Most of the instrument's function however keep ill-understood

What Astronomical Knowledge Did Carolingian Scholars Managed to Reach?

Starting about from scratch as their source were scarce and with few instruments, the scholars, in the Carolingian times, made some basic discoveries however, mostly in terms of orbital science. We have diagrams figuring several planets' orbits unto the background of the Zodiac and showing the apsides (the farter and closer the Earth) and the parts of latitude above or below, of the orbits. Above all, each orbit has a center of it own, meaning that such drawings are not mere representations of what could be observed against the starry night but really theoretical, astronomical models. Such drawings also may figure the famed Z-shaped trajectory of a planet at the moment of its opposition which means that, even without the Greek concept of the epicycle Carolingian teachers were well rendering the apparent stations and retrograde motion on a planetary orbit! Whence they were really able to build more complex theories about apsides, latitudes, and retrograde motions or eccentricity as related to the Sun, likely reaching about the concept of inclination or eccentricity. All such knowledge largely is seen circulating among the Carolingian schools of the Empire and down to Italy, Spain and England. The Aratus, a high level work, for example, is a comprehensive synthesis of such views with all the planetary orbits figured and possibly matching a March 18th, 816 A.D. of our solar system. Another synthesis was available at the court at the time under the form of that famed silver table owned by Charlemagne, which included a complete description of the celestial sphere and the behavior of the stars and planets and Louis the Pious inherited it. Such advances, on the other hand, as they are based too upon field observations, are showing that that era was able to construct theoretical views from observation, which may be considered a science move! Despite this, that science could not go beyond the current views of the solar system as perpetuated through Martianus Capella, with a hybrid view of our solar system, the Sun and Moon orbiting around the Earth with 3 planets as Mercury and Venus are orbiting the Sun. The written records of the work in astronomy are few on the other hand, as Archbishop Arn only, in Salzburg, had his 'Astronomical Notices' written down

Another field of the Carolingian advances in terms of astronomy were made in terms of calendar and time-keeping. By the Early Middle Ages, the solstice and equinox dates never fell accurate and did not were in agreement with skies and seasons. By the end of the 9th century progresses too were made, with better methods and better results. Heiric of Auxerre (860-903) 'Ars calculatoria' used the light ray passing through a slit in the eastern wall of the monastery's refectory by sunrise during several days in a row and shining on the western wall, inventing the pinpoint method! Other scholars during the 10 century saw that the vernal equinox at the time did not occur by March 21st but as soon as by March 17 or 18. It was not until 1069 A.D., with Wilhelm von St Emmeram, that a new instrument in Regensburg, the 'Sphaera', was deviced and allowed to the dates of solstices and equinoxes, dating the vernal equinox on March 16th. Further studies kept in the 11th century a interest, this way, into computus, arithmetics, geometry and astronomy in the monastic schools. On a other hand, like a useful tool to check the night prayer time, deacon Pacificus, who teached in the cathedral school of Verona, Italy, as he lived until in 844 A.D., designed a instrument in which a aiming tube was associated with a disk divided into 24 hours. It allowed to check time at night trough the revolution of Polaris around the celestial pole. Polaris at the time was not lying close to the celestial pole like nowadays but some 2 degree apart and thus revolving there. Pacificus thus had built a 'horologium nocturnum' as he was naming Polaris the 'noctium horarum computatrix', the 'one which computes the night times!' Efforts still existed in the Carolingian times to replace pagan solar festivals with Christian festivals. It even is possible that Church tended to rescue astrology for its own purpose. It's possible, for example, that the cathedral at Aachen might have accomodated symbolic beams of sunlight at the solstices, equinoxes and other significant dates. The golden sphere suspended from a chain in the center of the church, is hit at noon by sunlight at the summer solstice

Conclusion

All in all, astronomy, in the Carolingian times, kept being what science was in the Christian Latin West, that is it had to be useful for the daily needs and to aid in the understanding of God. Astronomy mostly was used to establish the calendar, to understand the motions of the heavens or to aid biblical exegesis. Added with, in some cases, some use in astrology. Any theoretical improvement, quantitative approach, or the role of observation kept being out of focus. Computistical texts just described the average motions, without variations therefrom, as stars were inaccurately placed within the constellations, for example. The advances in astronomy like we described those just above surely have to be replaced in the time as they likely rarely opened to any major advances into the representation they had at the time of the Universe at large. The work performed however is showing how the Western brains could manage to science from their own and able to develop a thought from some simple basics. Astronomy mostly remained about copying the ancient works. Like any other domain of knowledge at the time, astronomy inserted itself into a comprehensive view with was a mix of texts from Antiquity, of practical worries with advances of the time often under the speculative type. Some areas of knowledge, on the other hand, can really be termed science, or technology as they are relying upon facts, be those studied for themselves or for some practical use. A other, unsanwered question is whether the Carolingian scholars had any contact with the astronomical knowledge of the Greek court and of the Arabs of Baghdad. The Byzantines had access to the classical knowledge of the Greeks, as the Arabs developed empirical astronomy -some concepts of which however will be used some centuries later like the basis for the Copernician revolution (in the Carolingian times, for example, a Persian astronomer, Al Sufi, about 924 or 964 A.D., does mention the Large Magellanic Cloud in his book 'The Book of the Fixed Stars'; he calls it 'Al Bakr' ('the white ox') and he knows that it is not observable from northern Arabia, or from Baghdad as it is more South, from the Bab el Mandeb Strait). It looks like the West, according to some, never knew at the time the astronomical tables from the Baghdad Observatory -despite, for example, the ambassies which were exchanged between Charlemagne and the Caliphate. Some Greek astrolabes as in use by the Arabs in southern or central Spain, managed to reach Catalunia, Germany and other Western kingdoms by the end of the Carolingian era, starting by 960 A.D. and until 1030 along with a terminology and a description of how to build and use one in Latin. A other such tool was seen appearing in Constanz by the 980's and astrolabes began to be used by Hermannus Contractus in Reichenau, Berthold in Konstanz or others in Augsburg, Fleury, Micy, Chartres, Laon, Lüttich, and Köln in the purpose of observing Moon's and planet's motion or to correct the Bede's calendar