Editing Almagest (section)

=== The ''Syntaxis Mathematica'' books ===
[[File:Ptolemy-4.jpg|alt=Table of contents to a 1528 copy of Almagest, translated to Latin from Greek by George of Trebizond|thumb|Table of contents to a 1528 copy of ''Almagest'', translated to Latin from Greek by [[George of Trebizond]]]]

The ''Syntaxis Mathematica'' consists of thirteen sections, called books. As with many medieval manuscripts that were handcopied or, particularly, printed in the early years of printing, there were considerable differences between various editions of the same text, as the process of transcription was highly personal. An example illustrating how the ''Syntaxis'' was organized is given below; it is a Latin edition printed in 1515 at Venice by Petrus Lichtenstein.{{sfn|Lichtenstein|1515|p={{Pages needed|date=April 2023}}}}

* '''Book I''' contains an outline of [[Aristotle]]'s cosmology: on the spherical form of the heavens, with the spherical Earth lying motionless as the center, with the [[fixed stars]] and the various [[planets]] revolving around the Earth. Then follows an explanation of [[chord (geometry)|chords]] with [[Ptolemy's table of chords|table of chords]]; observations of the obliquity of the [[ecliptic]] (the apparent path of the Sun through the stars); and an introduction to [[spherical trigonometry]].
* '''Book II''' covers problems associated with the daily motion attributed to the heavens, namely risings and settings of celestial objects, the length of daylight, the determination of [[latitude]], the points at which the [[Sun]] is vertical, the shadows of the [[gnomon]] at the [[equinox]]es and [[solstice]]s, and other observations that change with the observer's position. There is also a study of the angles made by the ecliptic with the vertical, with tables.
* '''Book III''' covers the length of the year, and the motion of the [[Sun]]. Ptolemy explains [[Hipparchus]]' discovery of the [[Precession (astronomy)|precession]] of the equinoxes and begins explaining the theory of [[epicycles]].
* '''Books IV''' and '''V''' cover the motion of the [[Moon]], lunar [[parallax]], the motion of the lunar [[apogee]], and the sizes and distances of the Sun and Moon relative to the Earth.
* '''Book VI''' covers solar and lunar [[eclipse]]s.
* '''Books VII''' and '''VIII''' cover the motions of the fixed stars, including precession of the equinoxes. They also contain a [[star catalogue]] of 1022 stars, described by their positions in the [[constellation]]s, together with [[ecliptic coordinates|ecliptic longitude and latitude]].{{refn|1= The catalogue actually contained 1,028 entries, but three of these were deliberate duplicates, because Ptolemy regarded certain stars as being shared between adjacent constellations. Three other entries were non-stellar, i.e. the Double Cluster in Perseus, M44 (Praesepe) in Cancer, and the globular cluster Omega Centauri.{{sfn|Ridpath|2023|loc=[http://www.ianridpath.com/startales/almagest.html "Ptolemy’s Almagest"]}} Ptolemy states that the longitudes (which increase due to [[precession]]) are for the beginning of the reign of [[Antoninus Pius]] (138 AD), whereas the latitudes do not change with time (but see [[#The star catalogue|the star catalog]]). The constellations north of the [[zodiac]] and the northern zodiac constellations (Aries through Virgo) are in the table at the end of Book VII, while the rest are in the table at the beginning of Book VIII. The brightest stars were marked first [[apparent magnitude|magnitude]] ({{mvar|m}}&nbsp;=&nbsp;1), while the faintest visible to the naked eye were sixth magnitude ({{mvar|m}}&nbsp;=&nbsp;6). Each numerical magnitude was considered twice the brightness of the following one, which is a [[logarithmic scale]]. (The ratio was subjective as no [[photodetector]]s existed.) This system is believed to have originated with Hipparchus. The stellar positions too are of Hipparchan origin, despite Ptolemy's claim to the contrary. Ptolemy identified 48 constellations: The 12 of the [[zodiac]], 21 to the north of the zodiac, and 15 to the south.{{sfn|Ridpath|2023|loc=[http://www.ianridpath.com/startales/almagest.html#48 Ptolemy’s 48 constellations]}}|group=note}}
* '''Book IX''' addresses general issues associated with creating models for the five [[naked eye planet]]s, and the motion of [[Mercury (planet)|Mercury]].
* '''Book X''' covers the motions of [[Venus]] and [[Mars]].
* '''Book XI''' covers the motions of [[Jupiter]] and [[Saturn]].
* '''Book XII''' covers stations and [[apparent retrograde motion|retrograde motion]], which occurs when planets appear to pause, then briefly reverse their motion against the background of the zodiac. Ptolemy understood these terms to apply to Mercury and Venus as well as the outer planets.
* '''Book XIII''' covers motion in latitude, that is, the deviation of planets from the ecliptic. The final topic of this chapter also covers how to determine when a planet first becomes visible after being hidden by the glare of the sun, as well as the last time it is seen before being hidden by the sun's glare.