Ophiuchus is a constellation lying on the celestial equator. It was originally listed by the Greek astronomer Ptolemy in the 2nd century. Its name means "snake-holder" in Greek and it is usually depicted as a man holding a huge snake with both hands. The snake is represented by the neighbouring constellation Serpens
The position of Ophiuchus splits the constellation Serpens
into two parts, Serpens Caput and Serpens Cauda (considered to be one constellation). Ophiuchus was previously known by its Latin name, Serpentarius, which also means "snake-holder."
It is uncertain which mythical figure the constellation represents, but it is usually associated with the healer Asclepius, the son of the Greek god Apollo, and, alternately, Asclepius' mentor, the centaur Chiron (who is usually associated with the constellation Centaurus
). Asclepius was said to have learned the secrets of healing after seeing one snake bring healing herbs to another. He became so skilled that he could even raise the dead. Zeus was worried by his ability and struck him dead with a bolt of lightning to make sure that the entire human race did not become immortal, but honoured him nonetheless by placing his image in the sky, to appease his son Apollo.
Ophiuchus occupies an area of 948 square degrees and contains five stars with known planets. It can be seen at latitudes between +80° and -80° and is best visible at 9 p.m. during the month of July. The Sun passes through the constellation between November 30 and December 17, which is why some astrologers consider Ophiuchus to be the thirteenth sign of the zodiac. It is, however, not included in most astrological zodiacs and belongs to the Hercules family of constellations.
Ophiuchus contains a number of notable stars. The brightest one is 
alpha Ophiuchi or Rasalhague ("the head of the serpent collector"), an A-type giant that marks the head of Ophiuchus.
eta Ophiuchi or Sabik is a binary system comprised of two main sequence stars. It is the northern pole star to Uranus. Together with 
zeta Ophiuchi, a hot blue giant that appears reddish because of interstellar dust, it marks the knees of Ophiuchus.
delta Ophiuchi (Yed Prior), a red giant 170 light-years distant, and 
epsilon Ophiuchi (Yed Posterior), a class G giant 108 light-years distant, form a naked eye optical double and mark Ophiuchus’ left arm. (Yed means "hand" in Arabic.)
beta Ophiuchi is a K-type giant star, also known as Cebalrai ("shepherd dog"), Cheleb, Kelb Alrai or Alrai.
kappa Ophiuchi or Helkath ("battlefield") is a magnitude 3 variable star approximately 85 light-years distant.
theta Ophiuchi is another magnitude 3 variable, lying approximately 565 light-years away from Earth. It is also known as Imad ("pillar") and Kaki ("lower leg").
nu Ophiuchi or Sinistra ("left" or "left hand") marks the right hand of Ophiuchus and has a brown dwarf for a companion.
RS Ophiuchi is a recurrent nova, produced by a white dwarf and a red giant in close orbit, approximately 5,000 light-years distant.
Two other stars in the constellation are notable for their proximity to the Sun. Barnard's Star, a low-mass red dwarf, is only 5.96 light-years away and the fourth closest star to the Sun, after the three stars in the alpha Centauri system in Centaurus
. It cannot, however, be seen by the naked eye because its apparent visual magnitude is about nine. The star was discovered by Edward E. Barnard in 1916. It is also notable for being a flare star, displaying sudden changes in light, which is unusual for old red dwarfs.
Barnard's Star is believed to be 11 to 12 billion years old, with a mass only 16 percent that of the Sun. It is approaching the Sun at 140 kilometres per second and will be only about 3.8 light-years away around the year 11,800.
The other star located relatively close to our Sun, approximately 13.8 light-years away, is Wolf 1061, another red dwarf.
Another significant feature in Ophiuchus is Supernova 1604, better known as Kepler’s Supernova or Kepler’s Star. It is a supernova that German astronomer Johannes Kepler observed in Italy in 1604 and Galileo later used to dispute the dogma that the heavens are changeless. The supernova remnant is still an object of interest in astronomy studies.
Ophiuchus contains several notable deep sky objects. IC 4665 is an open cluster with about 30 member stars, approximately 1,400 light-years distant. NGC 6633 is another open cluster with 30 stars, almost the size of the full moon.
NGC 6333 or Messier 9 is a globular cluster, one of the nearest ones to the centre of the Milky Way. It is about 25,800 light-years distant from Earth. NGC 6254 or Messier 10 is another globular cluster about 14,300 light-years distant. NGC 6218 or Messier 12 is a loose globular cluster that lies close to Messier 10. It contains at least 13 variable stars. NGC 6402 is also a globular cluster, one that has several hundreds of thousands of stars and at least 70 variables among them. A nova was observed in the cluster in 1938. NGC 6273 or Messier 19, originally documented as a comet-like object by Charles Messier, is an oblate globular cluster lying very close to the Galactic Centre.
NGC 6240 is an ultraluminous infrared galaxy, formed as a result of a merger between two smaller galaxies, with two distinct nuclei that can be observed in it.
Finally, IC 4603-4604 is a diffuse nebula in Ophiuchus, located near 
alpha Scorpii, Antares.
Ophiuchus belongs to the Hercules family of constellations, along with Hercules
, Corona Australis
, Triangulum Australe
Constellations directly bordering Ophiuchus are Hercules
, Serpens Cauda
, Serpens Caput