|
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 follows 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 listed 1,028 objects forming the classical 48 constellations. Three
stars were deliberately entered twice, since he regarded them as being shared
by two constellations. The star he 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 the southern fish, Piscis Austrinus; this is the star we call Fomalhaut. The star on the right ankle of Auriga also marked the tip of the northern horn of Taurus; we now know it as Beta Tauri. And 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.
We now know that another three objects in Ptolemy’s catalogue are actually not stars at all: the Double Cluster in Perseus (see below), M44 (Praesepe) in Cancer, and the globular cluster Omega Centauri. Reducing
the total further, the stars 18 and 20 in Cetus are now thought to be
duplicates of Cetus 17 and 19. So the total number of separate stars in the Almagest is 1,020. The number of stars Ptolemy catalogued in each constellation ranged
from a mere two in Canis Minor to 45 in Argo Navis.
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.
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, which 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 – 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. The letter S in the column
before the latitude stands for septentrionalis, meaning northern (the word is in reference to the seven stars of the Plough,
which define the northern sky). The first entry in Perseus is described as ‘nebulous’, and this is the famous Double Cluster in the 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 (‘Lucida earum que sunt in capita Algol’), ‘the bright one in the head of the Demon’, shows an Arabic influence, since Algol is an Arab name; in the original Greek,
Ptolemy had called this the Gorgon’s head, in line with Greek mythology, which in Latin would be ‘Gorgoneo’.
At the end of some constellations, Ptolemy listed what he called ‘unformed’ stars (informatae) 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.
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).
|
|
|||||||||||||||||||
|
|
|
| ||||||||||||||||||
