'''Almagest''' is the
Latin form of the
Arabic name (''al-kitabu-l-mijisti'', i.e. "The Great Book") of a mathematical and
astronomical treatise proposing the complex motions of the
stars and
planetary paths, originally written in
Greek as ''μαθηματικἠ σύνταξις'' (''Mathematike Syntaxis'', "Mathematical Treatise"; later titled ''Hè Megalè Syntaxis'', "The Great Treatise") by
Ptolemy of
Alexandria,
Egypt. The date of ''Almagest'' has recently been more precisely established. Ptolemy set up a public inscription at
Canopus in Egypt in 147/148 A.D. The late N. T. Hamilton found that the version of Ptolemy's models set out in the ''Canopic Inscription'' was earlier than the version in ''Almagest''. Hence ''Almagest'' cannot have been completed before about A.D. 150, a quarter century after Ptolemy began observing.
[1] Its
geocentric model was accepted as correct for over a thousand years in Arab and
European societies. The ''Almagest'' is our most important source of information on ancient
Greek astronomy. The Almagest has also been valuable to students of mathematics because it provides information on the ancient Greek mathematician
Hipparchus' work, which has been lost. Hipparchus wrote about trigonometry, but since his works have been lost mathematicians use Ptolemy's book as their source for information on Hipparchus' works and ancient Greek trigonometry in general.
Contents of the Almagest
The ''Almagest'' consists of thirteen books. Their subject matter can be summarized as follows:
★ Book I contains an outline of
Aristotelian cosmology, a set of
chord tables, 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, and the length of daylight.
★ Book III covers the motion of the
Sun.
★ Books IV and V cover the motion of the
Moon, lunar
parallax, and the sizes and distances of the Sun and Moon relative to the
Earth.
★ Book VI covers solar and lunar
eclipses.
★ Books VII and VIII cover the motions of the fixed
stars, including
precession of the
equinoxes. They also contain a
star catalogue. The brightest stars were marked of the first
magnitude (m = 1), while the faintest were of sixth magnitude (m = 6), the limit of human visual perception (without the aid of a telescope). Each grade of magnitude was considered to be twice the brightness of the following grade (a logarithmic scale). This system is believed to have originated with
Hipparchus. The stellar positions too are of Hipparchan origin, despite Ptolemy's claim to the contrary.
★ Book IX addresses general issues associated with creating models for the five
naked eye planets, as well as the motion of Mercury.
★ Book X covers the motions of Venus and Mars.
★ Book XI covers the motions of Jupiter and Saturn.
★ Book XII covers stations and
retrogradations, which occur 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 (the deviation of planets from the
ecliptic, the apparent path of the Sun through the stars).
Ptolemy's Cosmos
The cosmology of the ''Almagest'' includes five main points, each of which is the subject of a chapter in Book I. What follows is a close paraphrase of Ptolemy's own words from Toomer's translation.
★ The celestial realm is spherical, and moves as a sphere.
★ The earth is a sphere.
★ The earth is at the center of the cosmos.
★ The earth, in relation to the distance of the fixed stars, has no appreciable size and must be treated as a mathematical point.
[1]
★ The earth does not move.
thumb
Ptolemaic Planetary Models
Ptolemy assigned the following order to the
planetary spheres, beginning with the innermost:
# Moon
# Mercury
# Venus
# Sun
# Mars
# Jupiter
# Saturn
# Sphere of fixed stars
Other classical writers suggested different sequences.
Plato (c. 427-c. 347 BC) made the Sun next in order after the Moon, while
Martianus Capella (5th century AD) put Mercury and Venus in motion around the Sun. Ptolemy's authority was preferred by most Islamic and late medieval European astronomers.
Ptolemy inherited from his Greek predecessors a geometrical toolbox and a partial set of models for predicting where the planets would appear in the sky.
Apollonius of Perga (c. 262-c. 190 BC) had introduced the
deferent and epicycle and the 'eccentric deferent' to astronomy.
Hipparchus (2nd century BC) had crafted mathematical models of the motion of the Sun and Moon. Hipparchus had some knowledge of
Mesopotamian astronomy, and he felt that Greek models should match those of the Babylonians in accuracy. He was unable to create accurate models for the remaining five planets.
In the ''Almagest'', Ptolemy adopted Hipparchus' solar model, which consisted of a simple eccentric deferent. For the Moon, he began with Hipparchus' epicycle-on-deferent, then added a device that historians of astronomy refer to as a 'crank mechanism'. He succeeded in creating models for the other planets, where Hipparchus had failed, by introducing a third device called the
equant.
The ''Almagest'' was written by Ptolemy as a textbook of mathematical astronomy. It explained geometrical models of the planets based on combinations of circles, that could be used to predict the motions of celestial objects. In a later book, the ''Planetary Hypotheses'', Ptolemy explained how to transform his geometrical models into three-dimensional spheres or partial spheres. In contrast to the mathematical ''Almagest'', the ''Planetary Hypotheses'' is sometimes described as a book of cosmology.
Impact of the ''Almagest''
Ptolemy's comprehensive treatise of mathematical astronomy superseded most older texts of Greek astronomy. Some were more specialized and thus of less interest; others simply became outdated by the newer models. As a result, the older texts ceased to be copied and were gradually lost. Much of what we know about the work of astronomers like Hipparchus comes from references in the ''Almagest''.
Ptolemy's ''Almagest'' became an authoritative work for many centuries, as this 16th-century portrait of him as a Renaissance mathematician shows
The ''Almagest'' in the Middle Ages and Renaissance
The first translations into Arabic were made in the 9th century, with two separate efforts, one sponsored by the
caliph Al-Ma'mun. By this time, the work was lost in
Europe, or only dimly remembered in
astrological lore. Consequently,
Western Europe rediscovered Ptolemy from translations of Arabic versions. In the
twelfth century a Spanish version was produced, later turned into
Latin under the patronage of Emperor
Frederick II. Another Latin version, this time directly from the Arabic, was produced by
Gerard of Cremona, who found his text in
Toledo in
Spain.
Gerard of Cremona was unable to translate many technical terms, even retaining the Arabic ''Abrachir'' for Hipparchus.
In the
15th century, a Greek version appeared in Western Europe, and Johannes Müller, better known as
Regiomontanus, made an abridged Latin version at the instigation of the brilliant
Greek churchman
Johannes, Cardinal Bessarion. At the same time, a full
translation was made by
George of Trebizond. It included a commentary that was as long as the original. The work of translation, done under the patronage of
Pope Nicholas V was intended to supplant the old translation. The new manuscripts were a great improvement; the new commentary was not, and aroused much heated criticism. The Pope declined the dedication of the translation, and Regiomontanus' translation had the upper hand for the next century and more.
Commentaries on ''Almagest'' were written by
Theon of Alexandria (extant),
Pappus of Alexandria (fragments), and
Ammonius (lost).
Modern editions
★ Two translations of the ''Almagest'' have been published in English. The first, by R. Catesby Taliaferro, was included in volume 16 of the
Britannica Great Books series. A more recent translation, by G. J. Toomer, ''Ptolemy's Almagest'', Princeton University Press, 1998 (ISBN 0-691-00260-6), is almost universally thought to be superior.
★ An older French translation (facing the Greek text), published in two volumes (1813 and 1816) by Nicolas B. Halma, is available online at the Gallica web site.
[2]
Footnotes
1. Almagest, Ptolemy, , , , , , Book I, Chapter 5
See also
★
Star cartography
References
★ James Evans, ''The History and Practice of Ancient Astronomy'', Oxford University Press, 1998 (ISBN 0-19-509539-1)
★ Olaf Pedersen, ''A Survey of the Almagest'', Odense University Press, 1974 (ISBN 87-7492-087-1)
★ Olaf Pedersen, ''Early Physics and Astronomy: A Historical Introduction'', 2nd edition, Cambridge University Press, 1993 (ISBN 0-521-40340-5)
External links
★
Online copy of the star catalog in the Almagest
★
Almagest Planetary Model Animations
★
Online luni-solar & planetary ephemeris calculator based on the Almagest
★
Ptolemy's Almagest. PDF scans of Heiberg's Greek edition, now in the public domain (Classical Greek)
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