Claudius Ptolemaeus (
Greek:
Klaúdios Ptolemaîos;
c. AD 90 –
c. 168), known in English as
Ptolemy ( ), was a
Roman citizen of
Greek or
Egyptian ancestry.
He was a
mathematician,
astronomer,
geographer,
astrologer and a poet of a single epigram
in the
Greek Anthology.
He lived in Egypt
under the
Roman Empire, and is believed
to have been born in the town of Ptolemais Hermiou
in the Thebaid.
He died in
Alexandria
around AD 168.
Ptolemy was the author of several scientific treatises, three of
which would be of continuing importance to later
Islamic and
European
science. The first is the astronomical treatise now known as the
Almagest (in Greek, Ἡ Μεγάλη
Σύνταξις, "The Great Treatise", originally Μαθηματικὴ Σύνταξις,
"Mathematical Treatise"). The second is the
Geography, which is a thorough
discussion of the geographic knowledge of the
Greco-Roman world. The third is the astrological
treatise known sometimes in Greek as the
Apotelesmatika
(Ἀποτελεσματικά), more commonly in Greek as the
Tetrabiblos (Τετράβιβλος "Four books"), and
in
Latin as the
Quadripartitum (or
four books) in which he attempted to adapt
horoscopic astrology to the
Aristotelian natural philosophy of his day.
Background
The name
Claudius is a
Roman
nomen; the
fact that Ptolemy bore it proves that he was a
Roman citizen. It would have suited custom if
the first of Ptolemy's family who became a citizen (whether it was
he or an ancestor) took the
nomen from a Roman called
Claudius, who was in some sense responsible for granting
citizenship. If, as was not uncommon, this Roman was the emperor,
the citizenship would have been granted between AD 41 and 68 (when
Claudius, and then
Nero, were emperors). The astronomer would also have
had a
praenomen,
which remains unknown. However, it may have been
Tiberius,
as that
praenomen was very common among those whose
families had been granted citizenship by these emperors.
Ptolemaeus (Ptolemy) is a
Greek name. It occurs once in Greek mythology, and is of Homeric
form. It was quite common among the Macedonian upper class at the
time of
Alexander the Great, and
there were several among Alexander's army, one of whom in 323 BC
made himself King of Egypt:
Ptolemy I
Soter; all the kings after him, until Egypt became a Roman
province in 30 BC, were also
Ptolemies. There is little evidence on the
subject of Ptolemy's ancestry (though see above on his family's
Roman citizenship), but most scholars and historians consider it
unlikely that Ptolemy was related to the royal dynasty of the
Ptolemies.
Beyond his being considered a member of Alexandria's
Greek society, few details of Ptolemy's life are
known. He wrote in
Ancient Greek and
is known to have utilised
Babylonian astronomical data. Although
a Roman citizen, most scholars have concluded that ethnically,
Ptolemy was a Greek, while some suggest that he was ethnically an
Egyptian, though
Hellenized.
He was often known in later Arabic sources as "the Upper Egyptian", suggesting that he may have had
origins in southern Egypt
.
Later
Arabic
astronomers,
geographers and
physicists referred to him by his
name in
Batlaymus.
Astronomy
The
Almagest is the only surviving
comprehensive ancient treatise on astronomy.
Babylonian astronomers had developed
arithmetical techniques for calculating astronomical phenomena;
Greek astronomers such as
Hipparchus had
produced geometric models for calculating celestial motions;
Ptolemy, however, claimed to have derived his geometrical models
from selected astronomical observations by his predecessors
spanning more than 800 years, though astronomers have for centuries
suspected that his models' parameters were adopted independently of
observations. Ptolemy presented his astronomical models in
convenient tables, which could be used to compute the future or
past position of the planets. The
Almagest also contains a
star catalogue, which is an
appropriated version of a catalogue created by Hipparchus. Its list
of forty-eight
constellations is
ancestral to the modern system of constellations, but unlike the
modern system they did not cover the whole sky (only the sky
Hipparchus could see). Through the Middle Ages it was spoken of as
the authoritative text on astronomy, with its author becoming an
almost mythical figure, called Ptolemy, King of Alexandria. The
Almagest was preserved, like most of Classical Greek
science, in
Arabic manuscripts
(hence its familiar name). Because of its reputation, it was widely
sought and was
translated twice into
Latin in the 12th century, once in Sicily and again in Spain.
Ptolemy's model, like those of his predecessors, was
geocentric and was almost universally accepted
until the appearance of simpler
heliocentric models during the
scientific revolution.
His
Planetary Hypotheses went beyond the mathematical
model of the
Almagest to present a physical realization of
the universe as a set of nested spheres, in which he used the
epicycles of his planetary model to compute the dimensions of the
universe. He estimated the Sun was at an average distance of 1210
Earth radii while the radius of the sphere of the fixed stars was
20,000 times the radius of the Earth.
Ptolemy presented a useful tool for astronomical calculations in
his
Handy Tables, which tabulated all the data needed to
compute the positions of the Sun, Moon and planets, the rising and
setting of the stars, and
eclipses of the
Sun and Moon. Ptolemy's
Handy Tables provided the model
for later astronomical tables or
zījes.
In the
Phaseis (
Risings of the Fixed Stars)
Ptolemy gave a
parapegma, a star
calendar or
almanac based on
the hands and disappearances of stars over the course of the solar
year.
Geography
Ptolemy's other main work is his
Geographia. This also is
a compilation of what was known about the world's
geography in the
Roman
Empire during his time. He relied somewhat on the work of an
earlier geographer,
Marinos of Tyre,
and on
gazetteers of the Roman and ancient
Persian Empire, but most of his
sources beyond the perimeter of the Empire were unreliable.
The first part of the
Geographia
is a discussion of the data and of the methods he used. As with the
model of the solar system in the
Almagest, Ptolemy put all
this information into a grand scheme. Following Marinos, he
assigned
coordinates to all the places
and geographic features he knew, in a
grid that spanned the globe.
Latitude was measured from the
equator, as it is today, but Ptolemy preferred in
book 8 to express it as
the length
of the longest day rather than
degrees of arc (the length of the
midsummer day increases from 12h to 24h as one
goes from the equator to the
polar
circle).
In books 2 through 7, he used degrees and put
the meridian of 0 longitude at the most western land he knew, the
"Blessed Islands", probably the
Cape
Verde
islands(not the Canary Islands
, as long accepted) as suggested by the location of
the six dots labelled the "FORTUNATA" islands near the left extreme
of the blue sea of Ptolemy's map here reproduced.
Ptolemy also devised and provided instructions on how to create
maps both of the whole inhabited world (
oikoumenè) and of the Roman provinces.
In the second part of the
Geographia he provided the
necessary
topographic lists, and
captions for the maps.
His oikoumenè spanned 180 degrees of
longitude from the Blessed Islands in the Atlantic Ocean
to the middle of China
, and about
80 degrees of latitude from The Shetlands
to anti-Meroe (east coast of Africa); Ptolemy was well aware that he knew about
only a quarter of the globe, and an erroneous extension of China
southward suggests his sources did not reach all the way to the
Pacific Ocean.
The maps in surviving manuscripts of Ptolemy's
Geographia,
however, date only from about 1300, after the text was rediscovered
by
Maximus Planudes. It seems
likely that the topographical tables in books 2-7 are cumulative
texts - texts which were altered and added to as new knowledge
became available in the centuries after Ptolemy (Bagrow 1945). This
means that information contained in different parts of the
Geography is likely to be of different date.
Maps based on scientific principles had been
made since the time of
Eratosthenes
(3rd century BC), but Ptolemy improved
projections.
It is known that a world map based on the
Geographia was on display in Autun
, France
in late
Roman times. In the 15th century Ptolemy's
Geographia began to be printed with engraved maps; the
earliest printed edition with engraved maps was produced in Bologna
in 1477, followed quickly by a Roman edition in 1478 (Campbell,
1987).
An
edition printed at Ulm
in 1482,
including woodcut maps, was the first one printed north of the
Alps. The maps look distorted as
compared to modern maps, because Ptolemy's data were inaccurate.
One reason is that Ptolemy estimated the size of the Earth as too
small: while
Eratosthenes found 700
stadia for a great circle degree on the globe, in the
Geographia Ptolemy uses 500
stadia. It is highly
probable that these were the same
stadion since Ptolemy
switched from the former scale to the latter, between the
Syntaxis and the
Geographia and severely
readjusted longitude degrees accordingly. If they both used the
Attic
stadion of about
185 meters, then the
older estimate is 1/6 too large, and Ptolemy's value is 1/6 too
small, a difference explained as due to ancient scientists' use of
simple methods of measuring the earth, which were corrupted either
high or low by a factor of 5/6, due to air's bending of horizontal
light rays by 1/6 of the Earth's curvature. See also
Ancient Greek units of
measurement and
History of
geodesy.
Because Ptolemy derived many of his key latitudes from crude
longest day values, his latitudes are erroneous on average by
roughly a degree (2 degrees for Byzantium, 4 degrees for Carthage),
though capable ancient astronomers knew their latitudes to more
like a minute. (Ptolemy's own latitude was in error by 14'.) He
agreed (
Geographia 1.4) that longitude was best determined
by simultaneous observation of lunar eclipses, yet he was so out of
touch with the scientists of his day that he knew of no such data
more recent than 500 years ago (Arbela eclipse). When switching
from 700 stadia per degree to 500, he (or Marinos) expanded
longitude differences between cities accordingly (a point 1st
realized by P.Gosselin in 1790), resulting in serious
over-stretching of the Earth's east-west scale in degrees, though
not distance. Achieving highly precise longitude remained a problem
in geography until the invention of the
marine chronometer at the end of the 18th
century. It must be added that his original topographic list cannot
be reconstructed: the long tables with numbers were transmitted to
posterity through copies containing many scribal errors, and people
have always been adding or improving the topographic data: this is
a testimony to the persistent popularity of this influential work
in the
history of
cartography.
Astrology

The mathematician Claudius
Ptolemy 'the Alexandrian' as imagined by a 16th century
artist
Ptolemy's treatise on
astrology, known in
Greek as the
Apotelesmatika ("Astrological Outcomes" or
"Effects") and in Latin as the
Tetrabiblos ("Four books"),
was the most popular astrological work of antiquity and also had
great influence in the
Islamic world and the
medieval Latin
West. The
Tetrabiblos is an
extensive and continually reprinted treatise on the ancient
principles of
horoscopic
astrology in four books (Greek
tetra means "four",
biblos is "book"). That it did not quite attain the
unrivaled status of the
Almagest
was perhaps because it did not cover some popular areas of the
subject, particularly
electional
astrology (interpreting astrological charts for a particular
moment to determine the outcome of a course of action to be
initiated at that time), and
medical
astrology.
The great popularity that the
Tetrabiblos did possess
might be attributed to its nature as an exposition of the art of
astrology and as a compendium of astrological lore, rather than as
a manual. It speaks in general terms, avoiding illustrations and
details of practice. Ptolemy was concerned to defend astrology by
defining its limits,
compiling astronomical
data that he believed was reliable and dismissing practices
(such as considering the
numerological
significance of names) that he believed to be without sound
basis.
Much of the content of the Tetrabiblos well have been collected
from earlier sources; Ptolemy's achievement was to order his
material in a systematic way, showing how the subject could, in his
view, be rationalized. It is, indeed, presented as the second part
of the study of astronomy of which the
Almagest was the
first, concerned with the influences of the celestial bodies in the
sublunar sphere. Thus explanations of a sort
are provided for the astrological effects of the
planets, based upon their combined effects of
heating, cooling, moistening, and drying.
Ptolemy's astrological outlook was quite practical: he thought that
astrology was like
medicine, that is
conjectural, because of the many variable factors to be
taken into account: the
race,
country, and
upbringing of a
person affects an individual's personality as much if not more than
the positions of the Sun, Moon, and planets at the precise moment
of their birth, so Ptolemy saw astrology as something to be used in
life but in no way relied on entirely.
Music
Ptolemy also wrote an influential work,
Harmonics, on
music theory and the mathematics of
music. After criticizing the approaches of his predecessors,
Ptolemy argued for basing musical intervals on mathematical ratios
(in contrast to the followers of
Aristoxenus and in agreement with the followers
of
Pythagoras) backed up by empirical
observation (in contrast to the overly theoretical approach of the
Pythagoreans). Ptolemy wrote about how
musical notes could be translated into mathematical equations and
vice versa in
Harmonics. This is called Pythagorean tuning
because it was first discovered by Pythagoras. However, Pythagoras
believed that the mathematics of music should be based on the
specific ratio of 3:2 whereas Ptolemy merely believed that it
should just generally involve
tetrachords
and
octaves. He presented his own divisions
of the tetrachord and the octave, which he derived with the help of
a
monochord. Ptolemy's astronomical
interests also appeared in a discussion of the "
music of the spheres."
Optics
His
Optics is a work that survives only in a poor Arabic
translation and in about twenty manuscripts of a Latin version of
the Arabic, which was translated by
Eugene of Palermo (circa 1154). In it
Ptolemy writes about properties of
light,
including
reflection,
refraction, and
colour. The
work is a significant part of the early
history of optics.
Named after Ptolemy
There are several characters or items named after Ptolemy,
including:
See also
Footnotes
- See 'Background' section on his status as a Roman citizen
- Select Epigrams from the Greek Anthology By John William
Mackail Page 246 ISBN 1406922943 2007
- Mortal am I, the creature of a day..
- Jean Claude Pecker (2001), Understanding the Heavens:
Thirty Centuries of Astronomical Ideas from Ancient Thinking to
Modern Cosmology, p. 311, Springer, ISBN 3540631984.
- Asger Aaboe,
Episodes from the Early History of Astronomy, New York:
Springer, 2001), p. 62-65.
- Alexander Jones, "The Adaptation of Babylonian Methods in Greek
Numerical Astronomy," in The Scientific Enterprise in Antiquity
and the Middle Ages, p. 99.
- Enc. Britannica 2007, "Claudius Ptolemaeus"
http://www.britannica.com/ebc/article-9376085
- "Ptolemy." Britannica Concise Encyclopedia. Encyclopædia
Britannica, Inc., 2006. Answers.com 20 Jul. 2008.
- Victor J. Katz (1998). A History of Mathematics: An
Introduction, p. 184. Addison Wesley, ISBN 0321016181.
- George
Sarton (1936). "The Unity and Diversity of the Mediterranean
World", Osiris 2, p. 406-463 [429].
- John Horace
Parry (1981). The Age of Reconnaissance, p. 10.
University of California
Press. ISBN 0520042352.
- Martin
Bernal (1992). "Animadversions on the Origins of Western
Science", Isis 83 (4), p. 596-607 [602,
606].
- J. F. Weidler (1741). Historia astronomiae, p. 177.
Wittenberg: Gottlieb. (cf.
Martin
Bernal (1992). "Animadversions on the Origins of Western
Science", Isis 83 (4), p. 596-607
[606].)
- Bernard R. Goldstein, "Saving the Phenomena: The Background to
Ptolemy's Planetary Theory", Journal for the History of
Astronomy, 28 (1997): 1-12
- S. C. McCluskey, Astronomies and Cultures in Early Medieval
Europe, Cambridge: Cambridge Univ. Pr. 1998, pp. 20-21.
- Charles Homer Haskins, Studies in the History of Mediaeval
Science, New York: Frederick Ungar Publishing, 1967, reprint
of the Cambridge, Mass., 1927 edition
- Dennis Duke, Ptolemy's Cosmology
- Bernard R. Goldstein, ed., The Arabic Version of
Ptolemy's Planetary Hypotheses, Transactions of the American
Philosophical Society, 57, 4 (1967), pp. 9-12.
- Mars Labs. Google Maps.
References
Texts and translations
- Berggren, J. Lennart, and Alexander Jones. 2000. Ptolemy's
'Geography: An Annotated Translation of the
Theoretical Chapters. Princeton and
Oxford: Princeton University Press. ISBN
0-691-01042-0.
- Hübner, Wolfgang, ed. 1998. Claudius Ptolemaeus, Opera quae
exstant omnia Vol III/Fasc 1: ΑΠΟΤΕΛΕΣΜΑΤΙΚΑ (= Tetrabiblos).
De Gruyter. ISBN 978-3-598-71746-8 (Bibliotheca scriptorum
Graecorum et Romanorum Teubneriana). (The most recent edition of
the Greek text of Ptolemy's astrological work, based on earlier
editions by F. Boll and E. Boer.)
- Nobbe, C. F. A., ed. 1843. Claudii Ptolemaei Geographia. 3
vols. Leipzig: Carolus Tauchnitus. (The most recent edition of the
complete Greek text)
- Ptolemy. 1930. Die Harmonielehre des Klaudios
Ptolemaios, edited by Ingemar Düring. Göteborgs högskolas
årsskrift 36, 1930:1. Göteborg: Elanders boktr. aktiebolag.
Reprint, New York: Garland Publishing, 1980.
- Ptolemy. 2000. Harmonics, translated and commentary by
Jon Solomon. Mnemosyne, Bibliotheca Classica Batava, Supplementum,
0169-8958, 203. Leiden and Boston: Brill. ISBN 9004115919
- Stevenson, Edward Luther (trans. and ed.). 1932. Claudius
Ptolemy: The Geography. New York: New York Public Library.
Reprint, New York: Dover, 1991. (This is the only complete English
translation of Ptolemy's most famous work. Unfortunately, it is
marred by numerous mistakes and the placenames are given in
Latinised forms, rather than in the original Greek).
- Stückelberger, Alfred, and Gerd Graßhoff (eds). 2006.
Ptolemaios, Handbuch der Geographie, Griechisch-Deutsch. 2
vols. Basel: Schwabe Verlag. ISBN 978-3-7965-2148-5. (Massive 1018
pp. scholarly edition by a team of a dozen scholars that takes
account of all known manuscripts, with facing Greek and German
text, footnotes on manuscript variations, color maps, and a CD with
the geographical data)
External links
Primary sources
Secondary material
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