Constellation

Constellation

Bibliography

See study by H. I. Chapelle and L. D. Polland (1970).

constellation

constellation, in common usage, group of stars that appear to form a configuration in the sky; properly speaking, a constellation is a definite region of the sky in which the configuration of stars is contained. Identifiable groupings of bright stars have been recognized and named since ancient times, the names corresponding to mythological figures (e.g., Perseus, Andromeda, Hercules, Orion), animals (e.g., Leo the Lion, Cygnus the Swan, Draco the Dragon), or objects (e.g., Libra the Balance, Corona the Crown). Ptolemy listed 48 constellations in his Almagest (2d cent. A.D.).

As systematic observations were extended to the entire southern sky from the 17th cent. on, more constellations were added to the list by J. Bayer, N. L. de Lacaille, and others. For example, Ptolemy's 48th constellation, Argo Navis, representing a ship, was divided into four smaller constellations corresponding to different parts of the ship. The final list consists of 88 constellations, each associated with a definite region of the sky. Thus, the entire celestial sphere is divided according to a plan prepared by Eugene Delporte, with the boundaries fixed by international agreement in 1930, along lines of right ascension and declination (see equatorial coordinate system). The 12 constellations located along or near the ecliptic, the apparent path of the sun through the heavens, are known as the constellations of the zodiac; the remaining constellations are officially classified as northern (28 constellations) or southern (48 constellations).

The table entitled Constellations lists the constellations according to their official Latin names, with the English equivalents and the approximate positions given. In some cases, the English name for a constellation is not an exact translation of the Latin; e.g., the English name for Pictor reflects the fact that the figure in the constellation is not the painter himself but his easel. Certain familiar star groups, or asterisms, are not listed as constellations because they form only part of a larger constellation; the Big Dipper and Little Dipper are parts of the constellations Ursa Major and Ursa Minor, and the Northern Cross is part of Cygnus.

Bright stars within a constellation are designated according to a system originated by Bayer in 1603: the brightest star is designated by the Greek letter alpha followed by the genitive form of the Latin name for the constellation, the second brightest star by beta, and so on, with Roman letters and pairs of Roman letters being used after the Greek letters have all been assigned. For example, the brightest star in Taurus, Aldebaran, is designated Alpha Tauri, the second brightest, Elnath, is designated Beta Tauri, and so on. The alphabetical order does not always indicate the stars' relative brightness: in a few cases, e.g., Ursa Major, the assignment of a Bayer name is according to position rather than brightness.

constellation

Originally the constellations had no fixed limits but were groups of stars considered by early civilizations to lie within the imagined outlines of mythological heroes, creatures, and other forms. In the Almagest , Ptolemy, in about ad 140, listed 48 constellations that were visible from the Mediterranean region. Their names were mostly derived from Greek and Roman mythology, which sought to explain their presence in the sky, but a few, such as Leo, the Lion, may be of much earlier origin. During the 16th, 17th, and 18th centuries many new groupings were identified and named (and several later discarded), especially in the previously uncharted regions of the southern hemisphere. These new groupings appeared principally in star atlases published by Bayer and Hevelius in the 17th century and Lacaille in the 18th. Since then further additions have proved unacceptable.

The constellations seen on any clear night depend on the latitude of the observer and change with the time of year and time of night. If, for a particular latitude, ⊂, the stars are circumpolar stars (never set), they will be visible on every night of the year. Circumpolar stars are those with declinations greater than 90 – ⊂°. Other stars never rise above the horizon at all: for observers in the northern hemisphere, these are the ones that have declinations beyond ⊂ – 90°; for observers in the southern hemisphere, they are the ones with declinations of ⊂ + 90° (note that southern latitudes, like southern declinations, are taken to be negative for these calculations). The remaining stars can be seen only when they are above the horizon during the night, a star rising earlier, on average, by about two hours per month.

Each constellation bears a Latin name, as with Canis Major, the genitive form of which is used with the appropriate letter or number for the star name (see stellar nomenclature), as with Alpha Canis Majoris. For simplification the three-letter abbreviations for the constellations are more usually used, as with CMa. See Table 5, backmatter.

An image of a Denderah constellation map, sometimes called the Denderah zodiac. The original is housed in the Louvre. Reproduced by permission of Fortean Picture Library.

Constellation

A constellation is a collection of stars that the ancients grouped together, identified with a figure from mythology, and named after that figure. In astrology, the names of the various signs of the zodiac are taken from 12 constellations intersected by the ecliptic. The untutored eye has a difficult time discerning the relationship between these star groups and the figures they are said to represent: Unlike the ancients, who gazed upon a sky filled with legends, heroes, and heroines, we moderns look up to see only a confused mass of tiny lights.

Constellation

constellation

constellation

Netscape Netcaster