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.

A constellation is any one of the 88 areas into which the sky — or the celestial sphere — is divided. The term is also traditionally and less formally used to denote a group of stars visibly related to each other in a particular configuration or pattern.

Some well-known constellations contain striking and familiar patterns of bright stars. Examples are Orion (containing a figure of a hunter), Leo (containing bright stars outlining the form of a lion), Scorpius (a scorpion), and Crux (a cross).

Division

The International Astronomical Union (IAU) divides the sky into 88 official constellations^[1] with precise boundaries, so that every direction or place in the sky belongs within one constellation. In the northern celestial hemisphere, these are mostly based upon the constellations of the ancient Greek tradition, passed down through the Middle Ages, and contains the signs of the zodiac.The sun appears to pass through the 12 constellations of the zodiac and ancient Greek astronomers believed they had a special significance.^{[citation needed]}

The constellation boundaries were drawn up by Eugène Delporte in 1930, and he drew them along vertical and horizontal lines of right ascension and declination. However, he did so for the epoch B1875.0, the era when Benjamin A. Gould made the proposal on which Delporte based his work. The consequence of the early date is that due to precession of the equinoxes, the borders on a modern star map (eg, for epoch J2000) are already somewhat skewed and no longer perfectly vertical or horizontal. This skew will increase over the years and centuries to come.

In three-dimensional space, most of the stars we see have little or no relation to one another, but can appear to be grouped on the celestial sphere of the night sky.

A star pattern may be widely known but may not be recognized by the International Astronomical Union; such a pattern of stars is called an asterism. An example is the grouping called the Big Dipper (North America) or the Plough (UK).

The stars in a constellation or asterism rarely have any astrophysical relationship to each other; they just happen to appear close together in the sky as viewed from Earth and typically lie many light-years apart in space. However, one exception to this is the Ursa Major moving group.

The grouping of stars into constellations is essentially arbitrary, and different cultures have had different constellations, although a few of the more obvious ones tend to recur frequently, e.g., Orion and Scorpius.

Greek constellation myths

The first ancient Greek works which dealt with the constellations were books of star myths. The oldest of these was a poem composed by Hesiod in the C8th BC, of which only fragments survive.

The most complete extant works dealing with the mythical origins of the constellations are by the Hellenstic writer termed pseudo-Eratosthenes and an early Roman writer styled pseudo-Hyginus. Each of these drew extensively from the writings of older sources (Hesiod and his successors) and provide a clear overview of the stories that lay behind the star groups we are familiar with today.

Dark cloud constellations

Members of the Inca civilization identified various dark areas in the Milky Way as animals, and associated their appearance with the seasonal rains. These areas are commonly referred to by modern researchers as dark cloud constellations.^[2]

Chinese constellations

Main article: Chinese constellation

Chinese constellations are different from the western constellations, due to the independent development of ancient Chinese astronomy. Ancient Chinese skywatchers divided their night sky in a different way, but there are also similarities. The Chinese counterpart of the 12 western zodiac constellations are the 28 "Xiu" (宿) or "mansions" (a literal translation).

Indian constellations

Main article: Nakshatra

Constellation names and star designations

All modern constellation names are Latin proper names or words, and some stars are named using the genitive, or sometimes the ablative of the constellation in which they are found. These are formed by using the usual rules of Latin grammar, and for those unfamiliar with that language the form of the genitive is sometimes unpredictable and must be memorized. Some examples include: Aries → Arietis; Taurus → Tauri; Gemini → Geminorum; Virgo → Virginis; Libra → Librae; Pisces → Piscium; Lepus → Leporis. In addition, all constellation names have a standard three-letter abbreviation assigned by the International Astronomical Union; for example, Aries becomes Ari, Pisces becomes Psc, Sagittarius becomes Sgr and Ursa Major becomes UMa [1].

Identification of stars within a given constellation includes use of Bayer designations such as Alpha Centauri, Flamsteed designations such as 61 Cygni, and variable star designations such as RR Lyrae. However, many fainter stars will just be given a catalog number designation (in each of various star catalogs) that does not incorporate the constellation name. Frequently, the abbreviated form of the constellation name is used in the star designation, e.g. Alpha Cen, 61 Cyg, RR Lyr.

For more information about star names, see star designations and the list of stars by constellation.

See also

• Chinese constellation
• Former constellations
• List of constellations
• List of constellations by area
• List of stars by constellation
• History of the constellations

Astronomy | Constellations of the Zodiac | Astrology
Aquarius	Pisces	Aries	Taurus	Gemini	Cancer	Leo	Virgo	Libra	Scorpio	Sagittarius	Capricorn

References

1. ^ Ian Ridpath. Constellation names, abbreviations and sizes (HTML). Retrieved on 2007-10-05.
2. ^ http://www.astronomy.pomona.edu/archeo/andes/inca.nightsky.html

External links

• Star Tales origins and mythology of the constellations (Ian Ridpath)
• The Constellations
• Photographic Atlas of the Constellations
• Celestia free 3D realtime space-simulation (OpenGL)
• Stellarium realtime sky rendering program (OpenGL)
• Strasbourg Astronomical Data Center Files on official IAU constellation boundaries (the older NASA ADC service does not function anymore)
• Interactive Sky Charts (Allows navigation through the entire sky with variable star detail, optional constellation lines)
• http://www.astronomical.org/portal/modules/wfsection/index.php?category=1
• http://www.seds.org/Maps/Stars_en/Fig/const.html
• Full constellation diagrams resembling their names
• Images of constellations
• Online Text: Hyginus, Astronomica translated by Mary Grant Greco-Roman constellation myths
• Observe satellites, space shuttles, constellations, comets
• Diagram showing three dimensional distribution of stars in Orionnds-nl:Konstelloatsienrm:Constellâtion

nov:Stelarozh-yue:星座

Donate to Wikimedia