The Universe: Constellations 4 - History channel.
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" In modern astronomy, a constellation is an internationally defined area of the celestial sphere. Historically, the term was also used to refer to a perceived pattern formed by prominent stars within apparent proximity to one another, and this practice is still common today.
A constellation is a group of celestial bodies, usually stars, which appear to form a pattern in the sky. Astronomers today still utilize 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 offically classed as a constellation is refered to as an asterism.
Typically, the modern constellations share the names of their greco-roman predecessors, such as Orion, Leo and Scorpius. While such celestial formations were originally linked to a mythical event, creature or person, the categorization of the night sky into recognizable 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 became important to move from a pattern-based system of constellations to one based on area-mapping, which led to several historic formations becoming obsolete.
Boundaries: 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 northern hemisphere and 51 to southern hemisphere.
Constellation systems around the world:
Graeco-roman: in the western world, the sky of the northern hemisphere is traditionally divided into constellations based on those described by the ancient greeks. 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 or around eighth century BC, of which only fragments survive. The most complete existing works dealing with the mythical origins of the constellations are by the hellenistic writer termed Eratosthenes and an early roman writer styled Hyginus. In the 2nd century AC, the greek astronomer Ptolemy described the constellations in great detail in his influential work the 'Almagest'.
Chinese: chinese constellations are different from the western constellations dus to the independent development of ancient chinese astronomy. One difference is that the chinese counterpart of the 12 western zodiac constellations is the 28 'xiu' or 'mansions'.
Indian: in vedic astrology, the 12 zodiac constellations are called raashees. The twelve raasis along the ecliptic correspond directly to the twelve western star signs. These are however divided into 27 nakshatras, or lunar houses.
Dark cloud constellations:
More visible and striking in the southern hemisphere than in the northern, dark patches in the Milky Way vividly stand out in Earth conditions when the Milky Way central region casts noticeable shadows on the ground. Some cultures have discerned shapes in these patches and have given names to these 'dark cloud constellations'. Members of the inca civilization identified various dark areas or dark nebulae in the Milky Way as animals, and associated their appearance with the seasonal rains. Australian aboriginal astronomy also describes dark cloud constellations, the most famous being the 'emu in the sky' whose head is formed by the Coalsack ".
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