Ptolemy’s Almagest
First printed edition, 1515
HERE is a page of the star catalogue from the first printed edition of Ptolemy’s Almagest, published in Venice in 1515. It is based on the Latin translation made by Gerard of Cremona (c.1114–1187) in Toledo, Spain, in 1175. Gerard worked from Arabic manuscripts, which were themselves translations of the Greek original. Ptolemy’s original manuscript is thought to have been produced around AD 150 and was long lost by Gerard’s time, a thousand years later, although copies survived, both in Greek and in Arabic.

Ptolemy listed 1,028 objects forming the classical 48 constellations (see the table at bottom of the page). Three stars were deliberately entered twice, since Ptolemy regarded them as being shared between constellations, as follows: 1, the star Ptolemy described as at the end of the flow of water from the urn of Aquarius was the same as the one in the mouth of Piscis Austrinus – this is the star we call Fomalhaut; 2, the star on the right ankle of Auriga also marked the tip of the northern horn of Taurus – we know it as Beta Tauri; 3, the star at the top of the staff of Boötes is the same as the one on the right foot of Hercules – we call it Nu Boötis.

Reducing the total further, we now know that another three objects in Ptolemy’s catalogue are actually not stars at all: the Double Cluster in Perseus; M44 (Praesepe) in Cancer; and the globular cluster Omega Centauri. Hence it is usually said that the Almagest contains 1,022 stars. However, the stars 18 and 20 in Cetus are now thought to be duplicates of Cetus 17 and 19 (DIO, vol. 12, p. 62, 2002, section C26). So the total number of separate stars in the Almagest is actually 1,020. The number of stars Ptolemy catalogued in each constellation ranged from a mere two in Canis Minor to 45 in Argo Navis.

almagestperseus.jpg

A page from the 1515 printing of the Almagest, showing the end of the star catalogue for Cassiopeia (top two lines) and the start of the listing of stars in Perseus. Note that the first entry in Perseus is described as ‘nebulosa’, i.e. nebulous.

Part of a sample page is illustrated above. The top two lines contain the last two stars in the listing for Cassiopeia. Following these is a line totalling the number of stars catalogued in Cassiopeia, as Ptolemy did at the end of every constellation (the Latin reads ‘Thirteen stars: four of the third magnitude, six of the fourth, one of the fifth, two of the sixth’). Then comes the start of the entry for Perseus, but the printed heading is not prominent so the book’s owner has written ‘Perseus’ by hand in the margin to make it easier to pick out.

Each star’s longitude and latitude is listed, as is its brightness on a scale from 1 to 6, the same principle as the modern magnitude scale – although Ptolemy himself did not use numbers but Greek letters, with alpha for first magnitude, beta for second, and so on. The letter S in the column before the latitude stands for septentrionalis, meaning northern in Latin (the word is in reference to the seven stars of the Plough, which define the northern sky). The first entry in Perseus is described in the magnitude column as ‘nebulous’ – this is the famous Double Cluster in the right hand of Perseus.

In the Almagest, Ptolemy identified stars not by letters or catalogue numbers, as we would do now, but by their position in the imaginary constellation figure. For example, Alpha Persei, the seventh star on the list, is described as ‘the bright star on the right side’ (‘Lucida que est in latere dextro’ in Latin), while the twelfth entry in this printed edition is called ‘Lucida earum que sunt in capita Algol’ (‘the bright one in the head of the Demon’). Here we see an Arabic influence, since Algol is an Arab name, which had crept in since Ptolemy’s time; in the original Greek, Ptolemy had called this the Gorgon’s head, in line with Greek mythology.

At the end of some constellations, Ptolemy listed what he called ‘unformed’ stars (informatae in Latin) that lay outside the recognized constellation pattern. Now that constellations are regarded as areas of sky rather than actual pictorial representations, these unformed stars have in most cases been absorbed into the related constellation or a neighbour. However, in some cases, later astronomers incorporated the orphan stars into new constellations. In the example shown below, Ptolemy lists 11 stars as lying outside Canis Major. Of these, the first is now in Monoceros and the fifth in Canis Major. The remainder were used by Petrus Plancius to form a new constellation, Columba.

almagestunformed.jpg

Above: Eleven ‘unformed’ stars around Canis Major, as listed in the Almagest. Nine of these later became part of a new constellation, Columba. The letter M before the latitudes stands for ‘meridionalis’, Latin for ‘southern’.


A scan of the complete 1515 printing of the Almagest can be downloaded from here. A scan of the detailed analysis of the catalogue by the astronomers C. H. F. Peters and E. B. Knobel published in 1915 can be downloaded here. Incidentally, in his Preface to the latter work, Knobel noted: “Notwithstanding Ptolemy's statement that he ‘observed as many stars as it was possible to perceive, even to the sixth magnitude,’ ... the catalogue is in all probability that of Hipparchus reduced by the addition of a constant to the longitudes”. For some more recent thoughts on the identification of various stars in the Almagest, see Keith Pickering’s article A Re-identification of some entries in the Ancient Star Catalog (DIO, vol. 12, pp. 62–63, 2002).

The Persian astronomer Abd al-Rahmān al-Sūfī revised and updated the Almagest in the 10th century, but Ptolemy’s catalogue was not fully superseded until the end of the 16th century when Tycho Brahe produced a thousand-star catalogue that was ten times more accurate, heralding a new era of star surveying.
Ptolemy’s 48 constellations
with the number of stars tabulated in each plus “unformed” stars outside the main figure
Ursa Minor
7 + 1
 
Cancer
9 + 4
Ursa Major
27 + 8
Leo
27 + 8
Draco
31
Virgo
26 + 6
Cepheus
11 + 2
Libra
8 + 9
Boötes
22 + 1
Scorpius
21 + 3
Corona Borealis
8
Sagittarius
31
Hercules
28* + 1
Capricornus
28
Lyra
10
Aquarius
42 + 3
Cygnus
17 + 2
Pisces
34 + 4
Cassiopeia
13
Cetus
22
Perseus
26 + 3
Orion
38
Auriga
14
Eridanus
34
Ophiuchus
24 + 5
Lepus
12
Serpens
18
Canis Major
18 + 11
Sagitta
5
Canis Minor
2
Aquila
9 + 6 (Antinous)
Argo
45
Delphinus
10
Hydra
25 + 2
Equuleus
4
Crater
7
Pegasus
20
Corvus
7
Andromeda
23
Centaurus
37
Triangulum
4
Lupus
19
Aries
13 + 5
Ara
7
Taurus
32** + 11
Corona Australis
13
Gemini
18 + 7
Piscis Austrinus
11*** + 6











































*      A 29th star was not counted as it was already included in the total for Boötes; this is now known as Nu Boötis.
**    A 33rd star was not counted as it was already included in the total for Auriga; this is now known as Beta Tauri,
***  A 12th star was not counted as it was already included in the total for Aquarius; it is now known as Alpha PsA (i.e. Fomalhaut).