Episodic Survey of the History of the Constellations

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O: Modern Western Constellations

26: Ptolemy's star catalogue

A late imaginary portrait of the Greek astronomer (and Roman citizen) Claudius Ptolemy (life dates circa 85 CE - circa 165 CE).

Greek manuscript of Ptolemy's Almagest in the Vatican Library. Dated to the 9th-century CE it is considered the oldest and most elegant of all the manuscripts of the Almagest. The pages show Book IV Chapter 2, on Hipparchus's examination of Babylonian cycles for the motion of the moon. The basis of Western astronomy as taught during Late Antiquity and until the Early Modern period is the Almagest by Ptolemy, written in the 2nd-century CE.

Ptolemy's Almagest devotes 2 chapters to the fixed stars. The total number of stars listed in his star catalogue is 1022. The most important of these are the 14 stars frequently used used by Ptolemy as fundamental reference stars. The term "cloudy stars" is first found in the Almagest of Ptolemy, but each of the 5 objects so named by him, nebulous to the eye, are coarse clusters of stars. Their nature was unknown until the invention of the telescope.

Claudius Ptolemy was born circa 85 CE in Egypt and died circa 165 in Alexandria in Egypt. He made his astronomical observations between circa 127 CE and 141 CE. Ptolemy was one of the most influential Greek astronomers and geographers of his time. However, very little is actually known of his life. His name, Claudius Ptolemy, combines a mix of the Greek Egyptian "Ptolemy" and the Roman "Claudius."

All of Ptolemy's major works have survived. The original Greek title of his most important work was The Mathematical Compilation (or The Great System of Astronomy) (but is now known by its popularised short Arabic title Almagest). The book was originally called Syntaxis by Ptolemy. Ptolemy's original Greek title was soon replaced by another Greek title The Greatest Compilation. Its commonly known title Almagest originates from its translation into Arabic as "al-majisti." (When Gherardo of Cremona translated the Arabic version of Ptolemy's work into Latin from the Arabic, in 1175, the al-Magisti become known as Almagest.) This thirteen book work, mostly concerned with presenting his original detailed geometric mathematical theory of the movements of the Sun, Moon, and planets, was his earliest and marks the high-point of Greek (Alexandrine) astronomy.

The first account of all 48 classical constellations was made by Eudoxus of Cnidos (circa 390-340 BCE). Poetic descriptions followed, such as Aratus' Phaenomena, the Catasterisms falsely ascribed to Eratosthenes of Cyrene (circa 275-194 BCE), the Poetica astronomica of Hyginus (2nd-century CE), derivative versions by Marcus Manilius (early 1st-century CE), Germanicus (early 1st-century CE) and Rufius Festus Avienus (4th-century CE), and also more scientific catalogue lists by Hipparchus and Ptolemy. Pseudo-Eratosthenes gave each constellation a mythological identity. These poetic/poetic-based works inclined towards "the transformation of the firmament into a rendezvous of mythological figures."

The earliest Western star catalogue (as we understand the term) originated with Ptolemy. The culmination of Greek establishment of constellation (and star) names was contained in (Book VII and Book VIII) of Ptolemy's Almagest written circa 140 CE. In it Ptolemy listed 1025 (fixed) stars. (The Almagest contained no star maps.) For his star catalogue Ptolemy used one system of coordinates (ecliptic longitudes and latitudes) for all the stars listed in it. Ptolemy did not identify the stars in his catalogue with Greek letters, as is done by modern astronomers. Each of the 1025 stars listed was identified (1) descriptively by its position within one of the 48 constellation figures; then (2) by its ecliptic latitude and longitude; and then (3) its magnitude. (Stars that did not fit into the figure of a constellation were sated to be outside the constellation and their position described in terms of their relationship to the nearest constellated stars.) It is this particular star catalogue method of Ptolemy that enables us to identify, with considerable exactness, the boundaries (i.e., shape) of the ancient Greek constellations. The identities of some of the stars in Ptolemy's list still remain completely uncertain due to errors in Ptolemy's measured coordinates and lack of precision in described positions.

The constellation list in Ptolemy's star catalogue standardised the Western constellation scheme. The constellation scheme described by Ptolemy consisted of 21 northern constellations, 12 zodiacal constellations, and 15 southern constellations.

The northern constellations: (1) Little Bear, (2) Great Bear, (3) Dragon [Draco], (4) Cepheus, (5) Ploughman, (6) Northern Crown, (7) Kneeler [Hercules], (8) Lyre, (9) Bird [Cygnus], (10) Cassiopeia, (11) Perseus, (12) Charioteer (Auriga], (13) Serpent Holder, (14) Serpent [Serpens], (15) Arrow, (16) Eagle, (17) Dolphin, (18) Forepart of Horse [Equuleus], (19) Horse, (20) Andromeda, (21) Triangle.

The zodiacal constellations: (1) Ram, (2) Bull, (3) Twins, (4) Crab, (5) Lion, (6) Virgin, (7) Scales [Claws], (8) Scorpion, (9) Archer, (10) Goat-horned, (11) Water-pourer, (12) Fishes.

The southern constellations: (1) Sea-Monster [Whale], (2) Orion, (3) River, (4) Hare, (5) Dog [Greater Dog], (6) Dog's Forerunner [Lesser Dog], (7) Argo, (8) Watersnake, (9) Bowl, (10) Raven, (11) Centaur, (12) Beast [Wolf], (13) Censer [Altar], (14) Southern Crown, (15) Southern Fish.

Of Ptolemy's 48 constellation figures, 14 (including Centaurus) represent men and women; 3 are birds, 14 are other land creatures; 7 are water creatures, and 10 are inanimate objects.

Note: The 12 named stars in the Almagest are: Arcturus, Regulus, Aselli, Sirius, Procyon, Vindemiatrix, Spica, Lyra (Vega), Capella, Aquila, Canopus, and Antares. Most of them lie in the Milky Way, to the right of the Milky Way, or very close to the Milky Way.

Ptolemy's Almagest, and its star catalogue, became dominant and influential for many centuries both in the Islamic world and in Western Europe. Classical science declined after the fall of Rome and science generally ceased to exist in Western Europe. Greek astronomy ended with the Arab conquest of Alexandria in 641 CE. However, the Arab-Islamic world kept classical knowledge alive by translating Hellenistic scientific texts into Arabic. The late 8th-century and the 9th-century saw a growing interest in Greek science in the Islamic world. At the end of the 8th-century a flourishing astronomical science had developed in the Arab-Islamic world. The Abbasid Caliph al-Ma'mūn initiated the heyday of the sciences in the Arab-Islamic world, first in Damascus and then later in Baghdad. (He specifically established a House of Wisdom in Baghdad.) In the 9th-century CE the Abbasid caliphs at Baghdad commissioned the translation from Greek into Arabic of a number of scholarly manuscripts. By the 8th-century the centre of astronomy had moved from Alexandria to Baghdad where Greek astronomical works were translated into Arabic (the scientific language of the Arab-Islamic world). Ptolemy's Almagest was first translated into Syriac and then into Arabic. (In the early centuries of the Christian Era the Christian sects (Nestorians, Monophysites, etc.) comprising the Middle Eastern churches began to hold doctrines that diverged from the doctrines of the churches established in Rome (Catholic) and Constantinople (Byzantium). The Nestorians in particular not only translated Greek religious texts into Syriac but also Greek philosophical, mathematical, and scientific treatises. Due to persecution by the Orthodox Church many Nestorians and some Monophysites migrated to the Persian Empire in Mesopotamia and Iran. There they established schools of intellectual and scholarly discussion, including translation and commentary of Greek texts in Syriac.)

The main transmission of Greek thought to the Arabs was made through the medium of the Syriac manuscripts produced by the great Nestorian school established at Jundishapur in Khuzistan (southwest Persia). It became the leading intellectual centre where writing in Greek and Sanskrit were translated into Syriac and Pahlawi. (The Nestorian sect of Christians was founded in 428 CE by Nestorius, patriarch of Constantinople (who settled in Persia under the Sasanian dynasty).) (See: Paul Kunitzsch, "Über einige Spuren der syrischen Almagestübersetzungen." In: Y. Maeyama & W. Saltzer (Editors ). PRISMATA: Naturwissenschaftliche Studien. Festschrift für Willy Hartner (1977, Pages. 203-210).) When the Islamic Arabs conquered Persia this knowledge became available in Arabic.

The earliest translations of the Almagest into Arabic are known to date to circa 800 CE. (Ptolemy's book on mathematical astronomy was translated twice into Arabic in the 9th-century CE.)

It is not known when and by whom the earlier Syriac translation was made. However there was more than one. The date of 7th and 8th centuries is established. Some persons identify the Jewish Rabbi Sahl al-Tabari as the earliest translator of the Almagest into Arabic. According to Gerald Toomer, in his English-language translation of the Almagest the first Arabic translation (from Syriac) was by al-Hasan ibn Quraysh, sometime prior to al-Hajj ibn Matar's translation in 827/8. According to Paul Kunitzsch (Der Almagest, 1974; and Der Sternenkatalog des Almagest: Die arabisch-mittelalterliche Tradition, 1986) the earliest documented translation was a Syriac translation, which predated the reigns of Harun-al-Rashid and al-Ma'mun. The 2nd oldest translation is the Old Arabic version, made either by al-Hasan-ibn-Quraysh (according to Ibn-as-Salah) or by Yahya ibn-Khalid (according to Ibn-al-Nadim), and which dated from around 780-820. All copies of both translations are lost, though fragments (significant subset?) are found in later works, most notably in al-Battani, al-Hajjaj and Ibn-as-Salah. A modern critical edition of al-Battani's Arabic text, with a new Latin translation, is given in C. A. Nallino, Albatenii Opus astronomicum (3 Volumes, 1899-1907). The oldest version which survived is from al-Hajjaj (827/8). Another version was made by Ishaq-bin-Hunayn, and was dated around 880-890. This version is also lost in its original form, but a thoroughly reworked (corrected) version by Al-Sabi Thabit ibn Qurra al-Harrani before 902 survived. According to Nasīr al-Dīn Tūsī (1271-1274), Al-Sabi Thabit ibn Qurra al-Harrani (836 –901) also wrote a completely independent translation of the Almagest, which is lost (in independent form). This makes 6 independent translations of the Almagest, all dating from the 9th-century, of which only 2 have come down to the present-day. According to Paul Kunitzsch, all currently known versions of the almagest we know are derived from those.

In the period after circa 1500 CE Arab-Islamic astronomy declined. In the 10th-century CE the power and patronage of the Baghdad caliphs began to decline, but Islamic astronomy continued to make advances in other parts of Islam. By the 11th-century the Baghdad Caliphate had lost control over much of its empire and weaker Caliphs were less inclined to encourage and finance scientific scholarship. The House of Wisdom and its library was destroyed in 1258 CE when the Mongol army ransacked Baghdad.

All knowledge of Ptolemy's Almagest was lost to Western Europe by the early middle ages. Until its decline in the 5th-century CE the city of Alexandria (in Egypt) was the centre of influence for Ptolemaic astronomy and texts. However, Ptolemy's Almagest in the original Greek continued to be copied and studied in the eastern (Byzantine) empire. In the 12th-century Spain became the conduit for the transmission of astronomical knowledge back into medieval Europe. This included the reintroduction of Ptolemy's works and additional Arab-Islamic astronomical texts. Effectively knowledge of Ptolemy's Almagest passed from Greece into the Islamic world then into Western Europe.

Appendix 1:

Claudius Ptolemy (and his predecessors) wrote in Greek. Because medieval scholars in Western Europe read only Latin, texts written in ancient Greek were effectively inaccessible. The knowledge of Latin scholars about the content of ancient Greek texts was limited to the summaries made by Roman authors.

Appendix 2:

Modern star catalogues give the position of the stars in a mathematical system of coordinates. Ancient 'star catalogs,' such as Ptolemy's 'star catalogue' were quite different and were not well-suited for astronomical observation. Their intention was more towards providing basic information on the stars comprising the constellation figures and the relative positions of the constellations, as well as explaining legendary aspects of the constellation figures.

The term "early star catalogues" is also commonly applied to descriptions of Greek (and Babylonian) uranography prior to Ptolemy. With few exceptions these "early star catalogues", however, are distinctly different from what modern astronomers, from Ptolemy onwards, have meant by the term. With few exceptions, prior to Ptolemy star catalogues did not give the position of stars by any system of mathematical coordinates. They are instead qualitative descriptions of the constellations. They simply note the number of stars in each part of a constellation and the general location of the brighter stars within a constellation. (The type of description usually used is "near X is Y".) This cumbersome method of describing the location of stars in terms of their relative positions in a constellation was used by both the Babylonians and the Greeks. The pictorial arrangement of stars is not a star catalogue. A star catalogue proper gives accurate positions for each individual star regardless of the constellation it is grouped into. Also, the boundaries of the Greek constellations were subject to change up to the time of Ptolemy.

In Greek astronomy the stars within the constellation figures were usually not given individual names. (There are only a few individual star names from Greece. The most prominent stars in the sky were usually nameless in Greek civilization. If there was a system of Greek star names then it has not come down to us and also would appear unknown to Ptolemy.) Greek constellations ("star catalogues") up to the time of Ptolemy are descriptive. The Western tradition of describing the constellations by means of describing the relative positions of the stars within the constellation figures was firmly established by Eratosthenes and Hipparchus. In their descriptions to the time of Ptolemy the constellations were defined by the Greeks by their juxtaposition (i.e., descriptive comparison of positional relationship to each other). Prior to Hipparchus (and Ptolemy) the general goal of the Greeks at least was not accurate astronomical observation but artistic and mythological education. The end result was a sort of geographical description of territorial position and limits.

Circa the 5th-century BCE many of the constellations recognised by the Greeks had become associated with myths. Both the star catalogue (constellation description) of Eudoxus (4th-century BCE) and the star catalogue (constellation description) of Aratus (3rd-century BCE) adopted the vocabulary of myth. In his Castasterismi Eratosthenes (284-204 BCE) completed and standardised this process with each of the constellations being given a mythological significance. The first complete description of the Greek constellations to survive is given by the Greek poet Aratus circa 270 BCE. With only a few exceptions no actual stars are described by Aratus - only constellation figures. This method was undoubtedly inherited from Eudoxus who produced a set of descriptions of constellations in which the relative positions of stars in each of the constellations was described. Eudoxus was likely the first Greek to summarise the Greek system of constellations. The purpose of the Phaenomena by Aratus was to describe the appearance and the organisation of the constellations in the sky with reference to each other.

Ancient 'star catalogues involved:

(1) Qualitative descriptions of the constellations.

(2) Noting the number of stars in each part of the constellations. (Describing the constellations by means of describing the relative positions of the stars within the constellation figures.)

(3) Noting the general location of the brighter stars within the constellations.

(4) Perhaps providing illustrations of the constellations to accompany the descriptions given.

(5) The illustrations depicting the mythological figures represented by the constellations (rather than the location and brightness of individual stars).

(6) The illustrations depicting the mythological figures represented by the constellations sometimes containing no stars at all - the body of each of the figures simply being filled with text discussing the particular constellation.


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