A glance at the heavens will make it evident that the problem of
designating a star in such a way as to distinguish it from all its
neighbors must be a difficult one. If such be the case with the
comparatively small number of stars visible to the naked eye, how must
it be with the vast number that can be seen only with the telescope?
In the case of the great mass of telescopic stars we have no method
of designation except by the position of the star and its magnitude;
but with the brighter stars, and, indeed, with all that have been
catalogued, other means of identification are available.
It is but natural to give a special name to a conspicuous star.
That this was done in very early antiquity we know by the allusion
to Arcturus in the Book of Job. At least two such names, Castor and
Pollux, have come down to us from classical antiquity, but most of the
special names given to the stars in modern times are corruptions of
certain Arabic designations. As an example we may mention Aldebaran, a
corruption of Al Dabaran--The Follower. There is, however, a tendency
to replace these special names by a designation of the stars on a
system devised by Bayer early in the seventeenth century.
This system of naming stars is quite analogous to our system of
designating persons by a family name and a Christian name. The family
name of a star is that of the constellation to which it belongs. The
Christian name is a letter of the Greek or Roman alphabet, or a number.
As a number of men in different families may have the same Christian
name, so the Greek letter or number may be given to a star in any
number of constellations without confusion.
The work of Bayer was published under the title of ‘Uranometria,’ of
which the first edition appeared in 1601. This work consists mainly
of maps of the stars. In marking the stars with letters on the map,
the rule followed seems to have been to give the brighter stars the
earlier letters in the alphabet. Were this system followed absolutely,
the brighter stars should always be called α; the next in order β,
etc. But this is not always the case. Thus in the constellation
_Gemini_, the brighter star is Pollux, which is marked β, while α is
the second brightest. What system, if any, Bayer adopted in detail
has been a subject of discussion, but does not appear to have been
satisfactorily made out. Quite likely Bayer himself did not attempt
accurate observations on the brightness of the stars, but followed the
indications given by Ptolemy or the Arabian astronomers. As the number
of stars to be named in several constellations exceeds the number of
letters in the Greek alphabet, Bayer had recourse, after the Greek
alphabet was exhausted, to letters of the Roman alphabet. In this
case the letter _A_ was used as a capital, in order, doubtless, that
it should not be confounded with the Greek α. In other cases smaller
italics are used. In several catalogues since Bayer, new italic
letters have been added by various astronomers. Sometimes these have
met with general acceptance, and sometimes not.
Flamsteed was the first Astronomer Royal in England, and observed at
Greenwich from 1666 to 1715. Among his principal works is a catalogue
of stars in which the positions are given with greater accuracy than
had been attained by his predecessors. He slightly altered the Bayer
system by introducing numbers instead of Greek letters. This had the
advantage that there was no limit to the number of stars which could
be designated in each constellation. He assigned numbers to all the
brighter stars in the order of their right ascension, irrespective
of the letters used by Bayer. These numbers are extensively used to
the present day, and will doubtless continue to be the principal
designations of the stars to which they refer. It is very common in
our modern catalogues to give both the Bayer letter and the Flamsteed
number in the case of Bayer stars.
The catalogues by Flamsteed do not include quite all the stars visible
to the naked eye, but various uranometries have been published which
were intended to include all such stars. In such cases the designations
now used frequently correspond to the numbers given in the uranometries
of Bode, Argelander and Heis.
In recent times these uranometries have been supplemented by censuses
of the stars, which are intended to include all the stars to the ninth
or tenth magnitude. I shall speak of these in the next section; at
present it will suffice to say that stars are very generally designated
by their place in such a census.
There is still here and there some confusion both as to the boundaries
of the constellations and as to the names of a few of the stars in
them. I have already remarked that, in drawing the imaginary boundaries
on a star map, as representing the celestial sphere, different
astronomers have placed the lines differently. One of the regions in
which this is especially true is in the neighborhood of the north pole,
where some astronomers place stars in the constellation Cepheus which
others place in Ursa Minor. Hence in the Bayer system the same star may
have different names in different catalogues. Again, in extending the
names or numbers, some astronomers use names which others do not regard
as authoritative. The remapping of the southern constellation by Dr.
Gould changed the boundaries of most of the southern constellations in
a way already mentioned.
I have spoken of the subdivision of the great constellation _Argus_
into four separate ones. Bayer having assigned to the principal
stars in this constellation the Greek letters α, β, γ, etc., the
general practice among astronomers since the subdivision has been to
continue the designation of the stars thus marked as belonging to the
constellation _Argo_. Thus, for example, we have _Argus_, which after
the subdivision belonged to the constellation _Carina_. The variable
star η Argus also belongs to the constellation _Carina_. But in the
case of stars not marked by Bayer, the names were assigned according to
the subdivided constellations, _Vela_, _Carina_, etc. Confusing though
this proceeding may appear to be, it is not productive of serious
trouble. The main point is that the same star should always have the
same name in successive catalogues. Still, however, it has recently
become quite common to ignore the constellation _Argus_ altogether and
use only the names of its subdivisions. The reader must therefore be
on his guard against any mistake arising in this way in the study of
astronomical literature.
In star catalogues the position of a star in the heavens is sometimes
given in connection with its name. In this case the confusion arising
from the same star having different names may be avoided, since a
star can always be identified by its right ascension and declination.
The fact is that, so far as mere identification is concerned,
nothing but the statement of a star’s position is really necessary.
Unfortunately, the position constantly changes through the precession
of the equinoxes, so that this designation of a star is a variable
quantity. Hence the special names which we have described are the most
convenient to use in the case of well-known stars. In other cases a
star is designated by its number in some well-known catalogue. But even
here different astronomers choose different catalogues, so that there
are still different designations for the same star. The case is one in
which action of uniformity of practice is unattainable.