Ophiuchus is a large constellation straddling the celestial equator.
Its name is from the Greek Ophioukhos; “serpent-bearer“, and it is commonly represented as a man grasping a snake.
The serpent is represented by the constellation Serpens. Ophiuchus was one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one of the 88 modern constellations. It was formerly referred to as Serpentarius and Anguitenens.
Ophiuchus lies between Aquila, Serpens, Scorpius, Sagittarius, and Hercules, northwest of the center of the Milky Way. The southern part lies between Scorpius to the west and Sagittarius to the east.
In the northern hemisphere, it is best visible in summer. It is opposite Orion. Ophiuchus is depicted as a man grasping a serpent; the interposition of his body divides the snake constellation Serpens into two parts, Serpens Caput and Serpens Cauda.
In contrast to Orion, from November to January (summer in the Southern Hemisphere, winter in the Northern Hemisphere), Ophiuchus is in the daytime sky and thus not visible at most latitudes. However, for much of the Arctic Circle in the Northern Hemisphere’s winter months, the Sun is below the horizon even at midday.
Stars (and thus parts of Ophiuchus, especially Rasalhague) are then visible at twilight for a few hours around local noon, low in the south. In the Northern Hemisphere’s spring and summer months, when Ophiuchus is normally visible in the night sky, the constellation is actually not visible, at those times and places in the Arctic when midnight sun obscures the stars. In countries close to the equator, Ophiuchus appears overhead in June around midnight and in the October evening sky.
History and mythology
There is no evidence of the constellation preceding the classical era, and in Babylonian astronomy, a “Sitting Gods” constellation seems to have been located in the general area of Ophiuchus.
However, Gavin White proposes that Ophiuchus may, in fact, be remotely descended from this Babylonian constellation, representing Nirah, a serpent-god who was sometimes depicted with his upper half human but with serpents for legs.
The earliest mention of the constellation is in Aratus, informed by the lost catalog of Eudoxus of Cnidus (4th century BCE):
To the Phantom’s back the Crown is near, but by his head mark near at hand the head of Ophiuchus, and then from it you can trace the starlit Ophiuchus himself: so brightly set beneath his head appear his gleaming shoulders. They would be clear to mark even at the midmonth moon, but his hands are not at all so bright; for faint runs the gleam of stars along on this side and on that. Yet they too can be seen, for they are not feeble. Both firmly clutch the Serpent, which encircles the waist of Ophiuchus, but he, steadfast with both his feet well set, tramples a huge monster, even the Scorpion, standing upright on his eye and breast. Now the Serpent is wreathed about his two hands – a little above his right hand, but in many folds high above his left.
To the ancient Greeks, the constellation represented the god Apollo struggling with a huge snake that guarded the Oracle of Delphi.
Later myths identified Ophiuchus with Laocoön, the Trojan priest of Poseidon, who warned his fellow Trojans about the Trojan Horse and was later slain by a pair of sea serpents sent by the gods to punish him. According to Roman era mythography, the figure represents the healer Asclepius, who learned the secrets of keeping death at bay after observing one serpent bringing another healing herb.
To prevent the entire human race from becoming immortal under Asclepius’ care, Jupiter killed him with a bolt of lightning but later placed his image in the heavens to honor his good works. In medieval Islamic astronomy (Azophi’s Uranometry, 10th century), the constellation was known as Al-Ḥawwaʾ, “the snake-charmer“.
Aratus describes Ophiuchus as trampling on Scorpius with his feet. This is depicted in Renaissance to Early Modern star charts, beginning with Albrecht Dürer in 1515; in some depictions (such as that of Johannes Kepler in De Stella Nova, 1606), Scorpius also seems to threaten to sting Serpentarius in the foot.
Ophiuchus is one of thirteen constellations that cross the ecliptic. It has therefore been called the “13th sign of the zodiac“. However, this confuses sign with the constellation.
The signs of the zodiac are a twelve-fold division of the ecliptic, so that each sign spans 30° of celestial longitude, approximately the distance the Sun travels in a month, and (in the Western tradition) are aligned with the seasons so that the March equinox always falls on the boundary between Pisces and Aries.
Constellations, on the other hand, are unequal in size and are based on the positions of the stars. The constellations of the zodiac have only a loose association with the signs of the zodiac and do not, in general, coincide with them.
In Western astrology, the constellation of Aquarius, for example, largely corresponds to the sign of Pisces. Similarly, the constellation of Ophiuchus occupies most (November 29 – December 18) of the sign of Sagittarius (November 23 – December 21).
The differences are due to the fact that the time of year that the sun passes through a particular zodiac constellation’s position has slowly changed (because of the precession of the equinoxes) over the centuries from when the Greeks, Babylonians, and Dacians through Zamolxis originally developed the Zodiac.