CONSTELLATION, a group or con figuration of stars, within certain bound aries, to which a definite name has been assigned, the name being generally ex pressed in its Latin for the sake of in ternational convenience and of exactness. This grouping is almost entirely arti ficial, though some of the configurations bear some resemblance to the object in dicated by the name.
Histary.---Before the invention of al manacs the risings and settings of the constellations were looked to by husband men, shepherds, and sea-faring men as the landmarks of the seasons, and of the weather which each season was expected to bring. The earliest description that we have of the constellations is the poem by Aratus, called "The Phenomena of Aratus," about 280 B. c. The Greek sphere used by Hipparchus, 125 B. c., ap pears to be the earliest known accurate representation of the positions and mag nitudes of the stars, and upon this they were grouped into 48 constellations. We know of this work through the descrip tion of it in Ptolemy's "Megale Syn taxis," A. D. 170. This was translated by the Saracens into Arabic, A. D. 813-82, and miscalled by them the "Almagest," and it is principally through translations of this work that we know of these 48 original asterisms. Various astronomers have since then added a host of others, but most of these have fallen into disuse.
Lettering the Stars.—In 1603 Bayer, in his "Uranometria," immortalized him self by the happy thought of assigning letters to the individual stars of each of the 48 constellations of the "Almagest" beginning with the Greek alphabet and following approximately the order of brightness of the stars, and then using the lower-case Roman letters where need ed to complete any constellation. Some confusion has arisen, especially in those extending far toward the S., in trying to identify all of Bayer's lettered stars. Ar gelander's "Uranometria Nova" is, how ever, accepted to-day, with a few trifling exceptions, as the correct interpretation of Bayer. Lacaille, at the Cape, 1751
1752, extended the same system to the southern constellations, and was also compelled to revise the lettering of a few of Bayer's most southern ones, which were very inaccurately delineated. As far N. as his work extended, to + 10° of declination, Dr. Gould also assigned let ters in the constellations still unlettered, Monorceros, Scutum, and Sextans. In the northern constellations added by Hevelius, or between his time and Ptol emy, and which had not been lettered, Bailey assigned a few Greek letters when publishing the "B. A. C." (British Asso ciation Catalogue) in 1845. These let ters will probably stand in any future revision of the northern heavens, though they are not very generally used by as tronomers to-day. It should also be noted that the last letters of the capital Roman alphabet, beginning with R, are reserved for the variable stars. This has been agreed upon since Argelander's time, and has compelled the abandonment of sev eral such letters assigned by Lacaille in the southern heavens to stars that are not variables. Flamsteed's numbers in each constellation of the stars observed by him are also extensively used as a system of naming individual stars. These numbers refer to the order in which the stars occur in each constella tion in his "Catalogus Britannicus." Other early catalogues of stars arranged in this way by constellations are often used as a means of naming individual stars, especially that of Hevelius, a capi tal H being used in this case. These numbers refer, not to the arrangement of the stars in Hevelius's original "Prodo miss Astrononzite" (1690), nor to Bailey's edition of it in the 13th volume of the "Memoirs of the Royal Astronomical So ciety," but to Flamsteed's edition of the catalogue as published in the third vol ume of the "Historia axlestis Britan ?Lica," London, 1725, and considerable confusion has at times arisen from igno rance of this fact.