Ptolemy’s Almagest
First printed edition, 1515
This 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.
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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.
The top two lines on the page 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
– 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
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 (informa) 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 nearest constellation. However, in
some cases, the stars were incorporated by later astronomers
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.
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Above: Eleven ‘unformed’ stars around Canis Major, as listed in the Almagest. Nine of these later became part of a new constellation, Columba.