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 stars. Together, the stars look like a picture. The word constellation comes from Latin: con-, meaning together and stella- meaning stars. Some examples of constellations are Ursa Major, Orion, and Andromeda.
People used constellations to tell the difference in the colors. Different places in the world may have different constellations, but today astronomy has a fixed set of 88 constellations. This set is based on the Greek set and later some southern constellations were added, for example Antlia - the air pump. Most constellations have names that come from Greek mythology, like Orion or Andromeda.
There are 12 constellations in the Zodiac. The Sun travels through the Zodiac once each year. There is also a thirteenth constellation Ophiuchus - the carrier of a serpent, which the Sun goes through. However, most people do not think that it is in the Zodiac.
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In modern astronomy, a constellation is an area of the celestial sphere, defined by exact boundaries. The term "constellation" can also be used loosely to refer to just the more prominent visible stars that seem to form a pattern in that area.
The 88 official constellations defined by the IAU (International Astronomical Union) are mostly based upon those of the ancient Greek tradition, passed down through the Middle Ages, which includes the 'signs of the zodiac,' twelve constellations through which the sun passes and which thus have had special cultural significance. The rest consist of constellations which were defined in the early modern era by astronomers who studied the southern hemisphere's skies, which were invisible to the Greeks.
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 the 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 pseudo-Eratosthenes and an early Roman writer styled pseudo-Hyginus.
In the 2nd century AD, the Greek astronomer Ptolemy described the constellations in great detail in his influential work the Almagest.
Chinese constellations are the way the ancient Chinese grouped the stars. They are very different from the modern IAU recognized constellations. This is due to the independent development of ancient Chinese astronomy.
In Vedic (Indian) astrology, the 12 zodiac constellations are called raasis. The twelve raasis along the ecliptic correspond directly to the twelve western star signs. These are however divided into 27 Nakshatras, or lunar houses.
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