Ptolemy’s Almagest

• The Almagest is a Mathematical and Astronomical Work by the Greco-Roman Astronomer Ptolemy (c.90-168 CE), describing the apparent motion of the Stars and Planets.
• It is based on a Geocentric Solar System, with the Earth at the centre of the Universe.

Description

• The Almagest contains a Star Catalogue, based on a Work by Hipparchus.
• The Almagest lists 48 Constellations.
• It also contains the observation of Sunspots.
• Ptolemy's Tetrabiblos is an Astrological Work that acts as a companion to the Almagest.

Ptolemy

• Claudius Ptolemaeus (c.90-168 CE) was a Greco-Roman Mathematician, Astronomer, Geographer and Astrologer living and working in Alexandria in Egypt.
• His Theories were still accepted by the Medieval World and were not challenged until 1543 by Nicolaus Copernicus with a Heliocentric System (the Sun at the centre).
• Most of the Work acknowledges the work of Hipparchus (c.190-120 BCE), or is believed to be derived from his work.

The Almagest (13 Books)

• Book I:
  • An outline of the Cosmos according to Aristotle, how the stars and planets revolve around the Earth.
  • An explanation and table of Chords, based on the work of Hipparchus.
  • Observations on the Obliquity of the Ecliptic
• Book II:
  • Heliacal Rising and Heliacal setting of the Stars.
  • How to calculate Latitude.
  • Observation of the Sun where it is vertical.
  • Shadow of the Gnomon at the Summer Solstice, Winter Solstice and the Vernal Equinox and the Autumnal Equinox.
  • A Table of the angles of the Ecliptic

• Book III:
  • The length of the year, and the motion of the Sun.
  • Description of the Precession of the Equinoxes as described by Hipparchus.
  • The theory of Epicycles.

• Book IV and V:
  • The Moon, Lunar Parallax, Lunar Apogee.
  • The distances and size of the Moon and Sun in relation to the Earth.

• Book VI:
  • Solar Eclipse and Lunar Eclipse.

• Book VII and VIII:
  • The motion of the Stars.
  • Precession of the Equinoxes.
  • Star Catalogue of 1,022 Stars and their position in the Constellations.
  • The Stars are graded in Magnitude of Brightness to the naked eye, from 1 – 6 (M1 – M6). The magnitude doubles with each increase.
  • Both Magnitude and Position are thought to be based on the work of Hipparchus.

• Book IX:
  • Description of the issues affecting working models for the five planets in the Seven Classical Planets System, which are those visible to the naked eye: Mercury, Venus, Mars, Jupiter and Saturn. The other two being the Sun and the Moon.
  • The Motion of Mercury.

• Book X:
  • The Motion of Venus and Mars.

• Book XI:
  • The Motion of Jupiter and Saturn.

• Nook XII:
  • Description of the Retrograde Motion of the Planets.

• Book XIII:
  • Description of he Planets deviation from the Ecliptic

Other Works

• Ptolemy's Tetrabiblos
  • Also known as the ‘Quadripartitum’ meaning ‘the four books’, it is an Astrological Work combining Astrology with the Philosophy of Aristotle. It serves as a companion Book to the Almagest.
• Ptolemy's Geographia

Alexandria, Egypt