Medieval Astronomy

ASTRONOMY in the Middle Ages

– The Pre-Eminence of Aristotle’s Physics.

– Observation and sense-experience are essential to understanding.

– Two Types of Matter and Their Characteristics.

– Corruptible (Terrestrial).

– It can be created and destroyed.

– It exists within Earth’s atmosphere.

– It moves in straight lines.

– Incorruptible (Celestial).

– It can be neither created nor destroyed.

– It exists in the Heavens.

– It moves in circles (which are perfect).

– The Perfectness of the Circle.

– Wandering stars moved in spheres.

– Culminated in Ptolemy’s Cosmology.

– Extraterrestrial bodies moved in complex pattern of associated spheres.

– It is more important for the theory to explain what is happening (“save the phenomena”) than to accurately describe the physical system.

– It is presumptuous to assume what is simple on Earth is simple in Heaven.

– The Long Winter after Ptolemy.

– In the centuries that followed Almagest, astronomy fell into serious decline.

– A few Islamic astronomers commented on the Almagest, but no significant alternative was proposed.

– Any differences were mainly philosophical – Ptolemy did not strictly abide by Aristotle’s physical assumption that the earth was the center of the universe.

– From the death of Ptolemy to the birth of Copernicus, not more than a dozen records which have accurate planetary positions.

Yet another unexplained phenomenon: Precession of the axis

– Trepidation of the spheres: Theory of trembling celestial spheres to explain unpredicted variation in the path of the heavenly bodies.

The Brewing Discontent with Ptolemy:

Ptolemy’s precession value was understated – that was observed.

Precession – The rotation of earth’s axis.

Trepidation – invented by Islamic astronomers and incorporated into astronomical procedures prior to 1000 AD.

A fudge factor of sorts.

Finalized in the 13th century, King Alfonso X supposed comment:

“If I had been around at creation, I would have given the Good Lord some hints.”

By 1500, trepidation was falling apart, and the philosophical dissent from Islam had crept into the Latin west, so, although not intended to be revolutionary, some kind of reform was thought necessary.