Constellation
(astronomy)
Constellation (astronomy), in astronomy,
any of 88 imagined groupings of bright stars that appear on the celestial
sphere (see Ecliptic) and that are named after religious or mythological
figures, animals, or objects. The term also refers to the delimited areas on
the celestial sphere that contain the named groups of stars.
The oldest known drawings of
constellations are motifs on seals, vases, and gaming boards from the Sumerians,
indicating that constellations may have been developed as early as 4000 bc. The constellation Aquarius was named
by the Sumerians after their god of heaven An, who pours the waters of
immortality upon the earth. The division of the zodiac into 12 equal signs was
known around 450 BC by the Babylonians. The northern constellations known today
are little different from those known by the Chaldeans and the ancient
Egyptians, Greeks, and Romans. Homer and Hesiod mentioned constellations, and
the Greek poet Aratus of Soli (circa 315-c. 245 bc)
gave a verse description of 44 constellations in his Phaenomena. The
Alexandrian astronomer and mathematician Ptolemy, in his Almagest, described 48
constellations, of which 47 are known today by the same name.
In the past many other peoples have
grouped stars in constellations, although their arrangements usually did not
correspond to those of the ancients. Some Chinese constellations, however,
resemble those of the ancients, indicating the possibility of a common origin.
At the end of the 16th century the first
explorers of the South Seas mapped the southern sky, which was largely unknown
to the ancients. New constellations were added by a Dutch navigator, Pieter
Dirckz Keyser, who participated in the exploration of the East Indies in 1595.
Subsequently, other southern constellations were added by the German astronomer
Johann Bayer, who published the first extensive star atlas in the Western
world, the Uranometria; by Johannes Hevelius; and by the French
astronomer Nicolas Louis Lacaille. Many others proposed new constellations, but
astronomers finally settled on a list of 88. The boundaries of constellations,
however, remained a matter of discussion until 1930, when definitive boundaries
were fixed by the International Astronomical Union.
The genitive forms of the names of
constellations, preceded by a Greek letter, are used to designate about 1300
bright stars; this system was introduced by Johann Bayer. The famous star Algol
in the constellation Perseus, for example, is called Beta Persei. The
accompanying table lists the constellations on which separate articles appear
in this encyclopedia.
People have grouped stars into
imagined patterns, called constellations, since ancient times. Ancient people
created these patterns to remember important people and events. Click on the
arrows to learn more about some of the constellations that appear in the skies of
the Northern Hemisphere.
Ursa Major is made up of many
stars that appear to form the shape of a bear. Ursa Major contains the Big
Dipper, a group of seven stars in the shape of a large cup with a long handle.
The handle of the dipper forms the bear’s tail and the cup is located near the
bear’s rear end. Ursa Major is best seen in the summer months.
Orion, named for a famous hunter
in Greek mythology, is the brightest constellation in the winter sky. It
includes eight bright stars in the shape of an hourglass. According to legend,
three stars in a row form the belt of Orion.
The constellation Pegasus is
named for the winged horse of Greek mythology. The constellation is made of a
group of stars that appear to form the front half of an upside-down horse.
Pegasus is best seen in the fall.
Cygnus is made of two rows of
stars that appear to form the shape of a flying swan. The two rows of stars
intersect, so they are also known as the Northern Cross. Cygnus is easiest to
see during the month of September.
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