Constellation
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Orion is a remarkable constellation, visible from most places on the globe at one time or another during the year. The constellation of Orion is the area outlined in the dashed yellow line. Orion contains a striking and well-known star pattern that has the form of a hunter. |
A
constellation is any one of the 88 areas into which the sky - or the
celestial sphere - is divided. The term is also often used less formally 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
Ursa Major (containing the
Big Dipper),
Orion (containing a figure of a hunter),
Leo (containing bright stars outlining the form of a lion) and
Scorpius (a scorpion). Other constellations do not encompass any discernible star patterns, and contain only faint stars.
The
International Astronomical Union (IAU) divides the sky into 88 official constellations 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 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, which means 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.
Humans excel at finding
patterns and throughout history have grouped together stars that appear close to one another.
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.
Our current list is based on those listed by the
Roman astronomer,
Claudius Ptolemy, who lived in
Alexandria,
Egypt.
In more recent times this list has been added to in order to fill gaps between Ptolemy's patterns. The Greeks considered the sky as including both constellations and dim spaces between. But Renaissance star catalogs by
Johann Bayer and
John Flamsteed required every star to be in a constellation, and the number of visible stars in a constellation to be manageably small.
The constellations around the South Pole were not observable by the Greeks. Twelve were created by Dutch navigators
Pieter Dirkszoon Keyser and
Frederick de Houtman in the sixteenth century and first cataloged by
Johann Bayer. Several more were created by
Nicolas Louis de Lacaille in his posthumous
Coelum Australe Stelliferum, published in
1763.
Other proposed constellations didn't make the cut, most notably
Quadrans Muralis (now part of
Boötes) for which the
Quadrantid meteors are named. Also the ancient constellation
Argo Navis was so big that it was broken up into several different constellations, for the convenience of stellar cartographers.
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 mythic 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), providing a clear overview of the stories which lay behind the star groups we are so familiar with today.
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).
All modern constellation names are
Latin proper names or words, and some stars are named using the
genitive of the constellation in which they are found. The genitive is formed 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 â†' Arietis; Taurus â†' Tauri; Gemini â†' Geminorum; Virgo â†' Virginis; Libra â†' Librae; Pisces â†' Piscium; Lepus â†' Leporis.
These names include
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.
For more information about star names, see
Star designations and the
list of stars by constellation.
*
List of constellations*
List of constellations by area*
Former constellations*
Chinese constellation*
Nakshatra*
Star Tales*
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/constellations/obs.html
*http://www.seds.org/Maps/Stars_en/Fig/const.html
*
Constellations Articles*
Full constellation diagrams resembling their names*
Images of constellations*
The Constellations presented by Utah Skies
*
Online Text: Hyginus, Astronomica translated by Mary Grant Greco-Roman constellation myths
