a. An arbitrary formation of stars perceived as a firgure or design, especially one of the 88 recognised groups named after characters from classical mythology and various common animals and objects.
b. An area of the celestial sphere occupied by one of the 88 recognised constellations.
2. The configuration of planets at the time of one's birth, regarded by astrologers as determing one's character or fate.
a. Any of the 88 groups of stars as seen from the earth and the solar system, many of which were named by the ancient Greeks after animals, objects, or mythological persons.
b. An area on the celestial sphere containing such a group.
3. A group of stars seen as forming a figure or design in the sky, especially one of 88 officially recognised groups, many of which are based on mythological traditions from ancient Greek and Middle Eastern civalizations.
4. An area of the sky occupied by one of the 88 recognised constellations. These irregularly defined areas completely fill the celestial sphere and divide it into non-overlapping sections used in describing the location of celestial objects.
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. Historically, the term was also used to refer to a perceieved pattern formed by prominent stars within apparent proximity to one another, and this practice is still common today.
In colloquial usage, a constellation is a group of celestial bodies, usually stars, which appear to form a pattern or picture in the sky. Astronomers today still utilise the term, though the current system focuses primarily on constellations as grid-like segments of the celestial sphere rather than as patterns. A star-pattern that is not officially classed as a constellation is referred to as an asterism. One famous example is the asterism known as the Big Dipper, a term unused by the International Astronomical Union (IAU) as the stars are considered part of the lager constellation of Ursa Major.
In 1922, Henry Norris Russell aided the IAU by dividing the celestial sphere into 88 offficial constellations. Typically, these modern constellations share the names of their Graeco-Roman predecessors, such as Orion, Leo, and Scorpius. While such celestial formations were originally linked to a mythical event, creature or person, the categorisation of the night sky into recognisable patterns was important in early land and naval navigation prior to the invention of the compass during the Age of Discovery. With the technical advancement of astronomy, it become important to move from a pattern-based system of constellations to one based on area-mapping, which led to several historic formations becoming obsolete.
In 1930, the boundaries between the 88 official constellations were devised by Eugene Delporte along vertical and horizontal lines of right ascension and declination from which 37 belong to the northern hemisphere and 51 to the southern hemisphere. However, the data he used originated back to epoch B1875.0, which was when Benjamin A. Gould first made the proposal to designate boundaries for the celestial sphere, a suggestion upon which Delporte would base his work. The consequence of this early date is that due to the preccesion of the equinoxes, the borders on a modern star map, such as epoch J2000, are already somewhat skewed and no longer perfectly vertical or horizontal. This effect will increase over the years and centuries to come.
The stars within a constellation rarely have any substantial astrophyscial relationship to one another, and their apparent proximity when viewed from Earth disguises the fact that they are far apart, some being much farther from Earth than others. However, there are some exceptions: many of the stars in the constellation of Ursa Major (including most of the Big Dipper) are approximate to one another, a phenomenon known as the Ursa Major moving group.
Alphabetical List of Constellation Names
(above) An amazing website, with each constellation name hyperlinked to a further source of information: position in the sky, when best viewed, etc... brilliant source for research...