Summary

     One must take care to distinguish between cosmology, astronomy, and astrology, especially as they were studied in the Middle Ages. Cosmology, the study of the nature of the cosmos, was primarily derived from Aristotle's On the Heavens. Aristotle's cosmology was adapted to take biblical references, such as the separation of the firmament and the waters into account. Astronomy was an observational approach to the heavens that seeked to use empirical results to devise adequate predictive tools. The source of most Middle Age knowledge on astronomy comes from Ptolemy's Almagest, in translations from both Greek and Arabic. Astrology is closely related to astronomy and cosmology in that it interprets the heavens, but it focuses on the power of the celestial bodies to influence events in the terrestial realm. This led to the philosophy of microcasm and macrocasm in which the actions in the heavens mirror those on earth. As Grosseteste stated, humanity is God's greatest creation, mirrored by the perfection of the heavenly realm. This belief was a product of the neoplatonic and stoic views on the heavens common in the epoch.     

     By the 12th century, however, translations of an array of classical works and commentaries, including Aristotle's work On the Heavens and Arabic commentaries regarding astronomy, flooded the scholarly scene. Such an abundance of knowledge contributed to medieval natural philosophy, not being focused on "science," such as empirical observation and experimentation, but logical reasoning based on previous texts. This reasoning manifested itself in two forms, texts and commentaries, which, as the name implies, comment on a specific text often with little emprical verification. Questiones, in which the author would pose a question to a particular text and then propose an answer, also became a popular form of scholarly expression. Because these were the most highly utilized forms, there arose no dominating text explaining the medieval conceptions of astronomy and cosmology.

Medieval Cosmology: 

    Medieval cosmology was based primarily on Aristotle's On the Heavens. Unfortunately, Aristotle's propositions did not always conform to the Christian biblical conception of the universe. Due to this discrepancy, several issues surrounding the cosmos arose. Most of those concerns were about suggestions that seemed to curtail the power of God and were therefore intolerable, such as the eternity of the universe, and the uniqueness, motions, and size of the earth. Scholars such as Moses Maimonodes, Nicole Gresme, and Jean Buridan addressed these issues in their commentaries.

     One important representitive of medieval cosmological studies was Robert Grosseteste, who wrote a number of studies in the first part of the thirteenth century. A central idea in Grosseteste's cosmology was light. The cosmos were created by God when he created light, which he deemed a dimensionless point of matter with a form. The point immediatly diffused itself into a large sphere, drawing matter with it and giving rise to the corporeal cosmos.Subsequent radiation and differentiation gave rise to celestial spheres and the characteristic features of the sublunar region. Much of Grosseteste's work involves a theme of microcosm and macrocosm. Humanity is God's greatest creation, and this simultaneously mirrors the divine nature and the structural principles of the created cosmos. Grosseteste also shared an early medieval belief in a homogeneous cosmos. In his cosmology, the heavens are made of finer stuff than the terrestrial substances, but the difference is quantitative rather than qualitative.

Astronomy: 

Medieval astronomy was distinct from cosmology largely by pedigree: cosmology was based on the writings and traditions of Aristotle, Sacrobosco, and other philosophers and commentators who wrestled with questions of why while mathematical astronomy stemmed from Ptolemy's Almagest and generally sought to answer questions of physical movement and prediction.  For a while early medieval scholars had little to no access to any of the mathematical astronomy produced by Hipparchus, Ptolemy and others.  Knowledge of astronomy was thus limited until the tenth and eleventh centuries when contact with Islam increased and people such as Gerbert of Aurillac contributed greatly to the resources available on astronomy.  Translations and commentaries floated into the Latin world as well as useful instruments like the astrolabe, a device used for observing star or planet's altitude at any point in the year.   Furthermore, major works of astronomy such as the Almagest and Al-Farghani's The Rudiments of Astronomy were translated more than once making them more available to scholars.  In the universities, teachers began to make their own accounts of important astronomical works and these were used as textbooks for students allowing for more knowledge (though usually basic) of astronomy to be passed down.  The Theorica Planeterum apparently became the chief textbook among universities.  Scholars  would then attempt to harmonize Ptolemy's mathematical astronomy with Aristotle's cosmology, but they ran into some of the same contradictions the Arabic world had.  One answer did come about that would later influence Copernicus - the physical sphere version of the Ptolemaic system. 

Astrology: 

Medieval astrology drew largely from Ptolemy's Tetrabiblos, which was translated in 1130.  Astrology was regarded as important and true, but not deterministic, as this would have conflicted with the Christian doctrine of free will.  Another primary text on the subject was Albumasar's Introduction to the Science of Astrology which drew largely on Tetrabiblos.  It placed much stock in the conjunctions of planets, when two or more planets lined up.  These moments were seen as turning points in history, the rarer the conjunction, the bigger the turning point. Albumasar drew also from Platonic ideas of the soul, infusing the idea that the soul descended from the cosmos, and therefore wants to return there. Medieval astrology was also Aristotelianized, with the adoption of Aristotle's metaphysics of matter, form, and substance, and also his notion of celestial bodies being the source of all motion. (Lindberg 275)  Astrology also became entwined with medicine and was considered by any able doctor in his works. 

Medieval views on the surface of the earth:

Primary Sources

Key Terms and Definitions

Tetrabiblos:  Ptolomy's famous and influential discussion of astrology

conjunctions: important turning points in astrology correlating to the special arrangements and alignments in the planets.

Toledan Tables:  Islamic Astronomical tables influential in western astronomy in the middle ages.

Alfonsine Tables:  The first set of astronomical tables calculated in the west.  They were also very widely used and influential in the west in the middle ages.

Impetus:  A force applied to a moving body that keeps it in motion.  First put forth by John Buridan in an explanation of the motion of the heavens.  God's impetus at the beginning and creation of the universe keeps the celestial spheres moving because there is no impedence to their motion.

Questiones:  The dominant form of Cosmological writings in the 14th through the 16th centuries.  The writings are in the form of questions that generally have yes or no answers, and then an answer is stated with an explaination. 

conjunction: when two or more planets form a straight line.

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