In ancient times the practice was adopted of imagining the figures of
heroes and animals to be so outlined in the heavens as to include in
each figure a large group of the brighter stars. In a few cases some
vague resemblance may be traced between the configurations of the stars
and the features of the object they are supposed to represent; in
general, however, the arrangement seems quite arbitrary. One animal or
man could be fitted in as well as another. There is no historic record
or trace as to the time when the constellations were mapped out, or of
the process by which the outlines were traced. The names of heroes,
such as Perseus, Cepheus, Hercules, etc., intermingled with the names
of goddesses, show that the constellations were probably mapped out
during the heroic age. No maps are extant showing exactly how each
figure was placed in the constellation; but in the catalogue of stars
given by Ptolemy in his ‘Almagest,’ the positions of particular stars
on the supposed body of the hero, goddess or animal are designated with
such precision as he had at command, in some fairly precise position of
the figure. For example, Aldebaran is said to have formed the eye of
the Bull. Two other stars marked the right and left shoulders of Orion,
and a small cluster marked the position of his head. A row of three
stars in a horizontal line showed his belt, three stars in a vertical
line below them his sword. In this way the position of the figure can
be reproduced with a fair degree of certainty.
In the well-known constellation _Ursa Major_, the Great Bear,
familiarly known as the Dipper, three stars form the tail of the
animal, and four others a part of his body. This formation is not
unnatural, yet the figure of a dipper fits the stars much better than
that of a bear. In Cassiopeia, which is on the opposite side of the
pole from the Dipper, the brighter stars may easily be imagined to form
a chair in which a lady may be seated without further difficulty. As a
general rule, however, the resemblances of the stars to the figure are
so vague that the latter might be interchanged to any extent without
detracting from their appropriateness.
In any case, it was impossible so to arrange the figures that they
should cover the entire heavens; blank spaces were inevitably left
in which stars might be found. In order to include every star in
some constellation, the figures have been nearly ignored by modern
astronomers, and the heavens have been divided up, by somewhat
irregular lines, into patches, each of which contains the entire figure
as recognized by ancient astronomers. But all are not agreed as to the
exact outlines of these extended constellations, and, accordingly, a
star is sometimes placed in one constellation by one astronomer and in
another constellation by another astronomer.
The confusion thus arising is especially great in the southern
hemisphere, where it has been intensified by the subdivision of one
of the old constellations. The ancient constellation _Argo_ covered
so large a region of the heavens, and included so many conspicuous
stars, that it was divided into four, representing various parts of a
ship--the sail, the poop, the prow and the hull.
Dr. Gould, while director of the Cordoba Observatory, during the years
1870 to 1880, constructed the ‘Uranometria Argentina,’ in which all
the stars visible to the naked eye more than 10 degrees south of the
celestial equator were catalogued and mapped. He made a revision of the
boundaries of each constellation in such a way as to introduce greater
regularity. The rule generally followed was that the boundaries should,
so far as possible, run in either an east and west or a north and south
direction on the celestial sphere. They were so drawn that the smallest
possible change should be made in the notation of the conspicuous
stars; that is, the rule was that, if possible, each bright star should
be in the same constellation as before. The question whether this new
division shall replace the ancient one is one on which no consensus of
view has yet been reached by astronomers. Simplicity is undoubtedly
introduced by Gould’s arrangement; yet, in the course of time, owing
to precession, the lines on the sphere which now run north and south
or east and west will no longer do so, but will deviate almost to any
extent. The only advantage then kept will be that the bounding lines
will generally be arcs of great circles.
When the heavens began to be carefully studied, two or three centuries
ago, new constellations were introduced by Hevelius and other
astronomers to fill the vacant spaces left by the ancient ones of
Ptolemy. To some of these, rather fantastic names were given; the Bull
of Poniatowski, for example. Some of these new additions have been
retained to the present time, but in other cases the space occupied
by the proposed new constellation was filled up by extending the
boundaries of the older ones.
At the present time the astronomical world, by common consent,
recognizes eighty-nine constellations in the entire heavens. In this
enumeration _Argo_ is not counted, but its four subdivisions are taken
as separate constellations.