In contemporary astronomy, the sky is divided into 88 regions called constellations, generally based on the asterisms (which are also called “constellations”) of Greek and Roman mythology. The number of 88, along with the contemporary scientific notion of “constellation”, was convention in 1922 by the International Astronomical Union in order to establish a universal pattern for professional astronomers, who defined constellations from then on as regions of the sky separated by arcs of right ascensions and declinations and grouped by asterisms of their historically most important stars, which cover the entire celestial sphere. The constellations along the ecliptic are called the zodiac.
The ancient Sumerians, and later the Greeks (as recorded by Ptolemy), established most of the northern constellations in international use today. When explorers mapped the stars of the southern skies, European and American astronomers proposed new constellations for that region, as well as ones to fill gaps between the traditional constellations. Not all of these proposals caught on, but in 1922, the International Astronomical Union (IAU) adopted the modern list of 88 constellations. After this, Eugène Joseph Delporte drew up precise boundaries for each constellation, so that every point in the sky belonged to exactly one constellation.
Some constellations are no longer recognized by the International Astronomical Union
a constellation is a group of stars that are considered to form imaginary outlines or meaningful patterns on the celestial sphere, typically representing animals, mythological people or gods, mythological creatures, or manufactured devices. The 88 modern constellations are defined regions of the sky together covering the entire celestial sphere.
Origins for the earliest constellations likely goes back to prehistory, whose now unknown creators collectively used them to relate important stories of either their beliefs, experiences, creation or mythology. As such, different cultures and countries often adopted their own set of constellations outlines, some that persisted into the early 20th century. Adoption of numerous constellations
The traditional Western constellations are the 48 Greek classical patterns, as stated in both Aratus’ work Phenomena or Ptolemy’s Almagest, though their existence probably predates these constellation names by several centuries. Newer constellations in the far Southern Sky were added much later since the 15th century until the mid-18th century
In 1928, the International Astronomical Union (IAU) ratified and recognized 88 modern constellations, with contiguous boundaries defined by right ascension and declination. Therefore, any given point in a celestial coordinate system lies in one of the modern constellations. Some astronomical naming systems give the constellation where a given celestial object is found along with a designation in order to convey an approximate idea of its location in the sky. e.g. The Flamsteed designation for bright stars consists of a number and the genitive form of the constellation name.
Former constellations are old historical Western constellations that for various reasons are no longer recognized or adopted as official constellations by the International Astronomical Union (IAU). Prior to 1930, many of these defunct constellations were traditionally identified by one or more countries or cultures. Some only lasted several decades but others continued over many centuries. All are now only
Some of the northern sky’s former constellations were often placed in the less populated stellar regions between the traditional brighter constellations just to fill any unassigned gaps. In the southern skies, new constellations were often created from about the 15th Century by voyagers who began journeying south of the equator. European countries like England, France, the Netherlands, German or Italian states, etc., often supported and popularised their constellation outlines. In some cases, differing constellations occupied areas using the same shared stars. Most of these former constellations can often be found mentioned in older books, star charts or star catalogs.
Standardisation of all the modern eighty-eight constellations names and boundaries was finally made by Eugene Delporte for the IAU in 1930, under a ratified international agreement, successfully removing any possible astronomical ambiguities between the nations. Nearly all former or defunct constellations mostly differ in their designated boundaries inasmuch as they have outlines that do not follow the exacting defined lines of right ascension and declination.
The 88 constellations depict 42 animals, 29 inanimate objects and 17 humans or mythological characters.
Each of the IAU constellations has an official 3 letter abbreviation. They are actually abbreviations of the genitive form of the constellation names, so some letters appearing in the abbreviation may come from the genitive form without appearing in the base name (as in Sge for Sagitta/Sagittae, to avoid confusion with Sagittarius, abbreviated Sgr).
The majority of the abbreviations are just the first three letters of the constellation, with the first character capitalised: Ori for Orion, Ara for Ara/Arae, Com for Coma Berenices. In cases where this would not unambiguously identify the constellation, or where the name and its genitive differ in the first three letters, other letters beyond the initial three are used: Aps for Apus/Apodis, CrA for Corona Australis, CrB for Corona Borealis, Crv for Corvus. (Crater is abbreviated Crt to prevent confusion with CrA.)
When letters are taken from the second word of a two-word name, the first letter from the second word is capitalised: CMa for Canis Major, CMi for Canis Minor.
The abbreviations are unambiguous, with two exceptions. Leo for the constellation Leo could be mistaken for Leo Minor (abbreviated LMi), and Tri for Triangulum could be mistaken for Triangulum Australe (abbreviated TrA).
For help with the literary English pronunciations, see the pronunciation key. There is considerable diversity in how Latinate names are pronounced in English. For traditions closer to the original, see Latin spelling and pronunciation.
Various other unofficial patterns exist alongside the constellations. These are known as “asterisms”. Examples include the Big Dipper/Plough and the Northern Cross. Some ancient asterisms, for example, Coma Berenices, Serpens, and portions of Argo Navis