The constellation Orion is one of the most recognized in the sky. The name is associated both with a set of stars in the sky, and a bounded region of the sky, marked in yellow.
In modern astronomy, constellation refers to 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.
Human perception versus reality
Constellations are normally the product of human perception rather than astronomical realities. 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, there are some exceptions. The famous star pattern known as the Big Dipper in North America or the Plough in the UK is almost entirely created by stars that are genuinely close together in astronomical terms; they are known as the Ursa Major moving club.
The grouping of stars into constellations is essentially arbitary, as different cultures have seen different patterns in the sky, although a few of the more obvious ones tend to recur frequently, e.g., Orion and Scorpius.
Official constellations
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 hermisphere's skies, which were invisible to the Greeks.
Boundaries
The constellation boundaries now used by the International Astronomical Union were drawn up in 1930 by Eugene Deporte. 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 this early date is that due to precession of the equinoxes, the borders on a modern star map (e.g., 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.
A star pattern may be widely known but may not be used by the International Astronomical Union . One famous example is the asterism known as the Big Dipper in North America or the Plough in the UK; this term is not used by the IAU as the stars are considered part of the larger constellation of Ursa Major.
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. 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 .
Identification of stars within a given constellation includes use of Bayer designation such as Alpha Centauri, Flamsteed designation 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 stars catalog) 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.
Western
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 Erastosthenes 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. The 48 constellations he described are still used by astronomers today.
Chinese
Chinese constellations are different from the Western constellations due to the independent development of ancient Chinese astronomy, although there are also similarities. One difference is that the Chinese counterpart of the 12 western zodiac constellations is the 28 "Xiu" or "mansions" (a literal translation).
Indian constellations
In Vedic 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.
Dark cloud constellations
In the southern hermisphere, it is possible to discern dark patches in the Milky Way. 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.
Phenomena of Constellation
Some stars can’t be seeing by some people on certain area in this earth. For example, people in Australia can’t see Polaris, which close with North Pole. Crux or south cross star is a star at south side sky that can’t be seeing from United Kingdom. Night sky that has constellations, which we see from Indonesia absolutely different with night sky in Netherland.
Sumber:
http://en.wikipedia.org/wiki/Constellation
http://langitselatan.com/2007/05/17/penghuni-langit-malam/
www.google.com
Nama: Monica Audina Sugiharto
XH/20
