Summary

     One must take care to distinguish between cosmology, astronomy, and astrology, especially as they were studied in the Middle Ages. Cosmology, the belief of the nature of the cosmos, mostly derived from Aristotle's On the Heavens. Aristotle's cosmology was adapted to take into account biblical references (e.g. the firmament and the waters, as well as the realm of the angels). 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 and his 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 lead to the philosophy of microcasm and macrocasm, which stated that 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 of texts and commentaries, which, as the name implies, comment on a specific text often with little emprical verification, and questions (or quaestiones), in which the author would pose a question to a particular text and then propose an answer. By utilizing these forms, there was no real dominating text that explained the medieval conceptions of astronomy and 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 were about the curtailing the power of God, such as the eternity of the universe, the uniqueness of the earth, the size of the earth, and its motions. 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.

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