Geocentrism Ptolemys Disorder Commentary

Claudius Ptolemy astronomy

Geocentrism

• Claudius Ptolemaeus of Alexandria
• wrote the definitive texts
• on astronomy and astrology
• in the second century.
• In the Almagest,
• Ptolemy described the obliquity of the ecliptic,
• shadows of gnomon at equinoxes and solstices,
• precession of the equinoxes,
• lunar parallax and apogee,
• solar and lunar eclipses,
• and retrograde motions of the planets.
• Ptolemy explained how the apparent motions
• of the stars, sun, moon, and the five planets,
• were described mathematically by a set of perfect spheres.
• Each planet circles in an epicycle.
• Each epicycle circles in a deferent.
• The center of all nested deferents
• is a point halfway between the stationary earth
• and the equant point.
• Ptolemy claimed that his celestial spheres
• were actually installed in the heavens—
• concentric transparent crystalline spheres
• spinning around above us.

Ptolemys

• Ptolemy, Ptolemy, not those Ptolemys.
• The other Ptolemys were pharaohs of Egypt
• starting with a fellow from Alexander’s army
• who made himself pharaoh in 323 BCE.
• Our Ptolemy died around AD 168
• and was not a pharaoh.
• Ours wrote a book on astronomy
• and one on geography.
• Wrote a book on astrology
• to match the one on astronomy.
• He wrote a book on harmonics
• and another on optics.
• All Ptolemys.

Disorder

• It would be nice
• if everything were
• somehow in control;
• however, total
• control would tend to
• stifle rock and roll.