The Almagest Archive

Notes from Alexandria

The Celestial Cartographer

Claudius
Ptolemy

c. 100 - c. 170 AD Alexandria

Book I, Chapter III

The
Almagest

That the heavens move spherically. It is reasonable to assume that the first ancients formulated these notions from the following kind of observation. They saw the sun, moon and other stars moving from east to west in circles always parallel to each other.

The Earth, sensibly, is entirely at rest and situated in the center of the heavens. The entire system revolves around this fixed point, an elegant mathematical necessity.

The Epicycle Hypothesis

To account for retrograde motion, celestial bodies inhabit smaller circles, epicycles, whose centers move along larger circles, deferents, centered on the Earth.

Study the proofs

A measured world

Geographia

A compilation of what is known about the world's geography in the Roman Empire of the 2nd century.

The known world is bounded...

Book I

Principles of Cartography

The task of geography is to present the known world as one and continuous, to describe its nature and position, and to include only such things as are of greater importance.

We must determine the positions of places by the observation of the heavens, setting down their latitudes and longitudes. A degree of a great circle of the earth measures 500 stades.

Fig 1. Projection

Celestial influence

Tetrabiblos

The Mathematical Treatise on the Influence of the Celestial Bodies

It is a matter of philosophical dispute whether the phenomena of the heavens impose absolute necessity upon terrestrial events, or if they merely incline the temperament toward certain dispositions. We here assert the latter, proposing a methodical inquiry into the rational principles governing cosmic sympathy.

Book I, Ch. 2

Of the Planets and Their Natures

The Sun is found to produce heat and moderate dryness; his power is greatest when he approaches our zenith. The Moon, conversely, diffuses moisture, her proximity to the Earth rendering her highly sensible to the exhalations of terrestrial elements. By observing these primary forces, the geometer constructs the framework of universal causation.

Let not the vulgar confound this mathematical discipline with the superstitious omens of the unlettered. The astrologer is a mathematician of the divine architecture, reading angles of incidence and the harmonies of spheres as one reads the very thoughts of the Demiurge.

Finis