"Certain people have said that he holds the snake for the following reason. [N.B. The following myth is usually told of the seer Polyidos rather than Asklepios.] When he was commanded to restore Glaucus, and was confined in a secret prison, while meditating what he should do, staff in hand, a snake is said to have crept on to his staff. Distracted in mind, Aesculapius killed it, striking it again and again with his staff as it tried to flee. Later, it is said, another snake came there, bringing an herb in its mouth, and placed it on its head. When it had done this, both fled from the place. Whereupon Aesculapius, using the same herb, brought Glaucus, too, back to life.
And so the snake is put in the guardianship of Aesculapius and among the stars as well. Following his example, his descendants passed the knowledge on to others, so that doctors make use of snakes." [Pseudo-Hyginus, Astronomica 2. 14 from Theoi website]
The astrological influences of the constellation given by Manilius:
Ophiuchus [the '13th sign'] - Dates: 30th November to 17th December
Definition: [Sun Signs - Solar Zodiac] Ophiuchus, the sign of the Serpent Bearer, is the 10th sign of the Real Solar Zodiac.
However, although it lies on the Ecliptic it is not one of the signs of either the Tropical Zodiac of standard Western Astrology, or the Sidereal Zodiac of standard Vedic astrology.
This problem is one of the most contentious issues in modern astrology. I know the subject of Ophiuchus causes us lots of grief as astrologers. But it's up there in the heavens. It exists. We can't ignore it.
The Thirteenth Sign? Ophiuchus is often mistakenly called the 'thirteenth sign of the zodiac' because the sign is thought of as an additional sign to the the twelve Tropical or Sidereal signs.
In fact, Ophiuchus is a Sun-sign in the Real Solar Zodiac, i.e. the Sun can be seen against the stars of Ophiuchus between 30th November and 17th December each year. [The dates of the cusps move a little from one year to the next, so sometimes they are quoted as 1st December to 18th December.] Aquarius, the Water Carrier, is the actual 13th, and last, sign of the Real Solar Zodiac.
Northern celestial hemisphere constellation map showing the sun sign of Ophiuchus between Scorpius and Sagittarius
The Centaur object, the minor planetoid Chiron, was visible against the stars of Ophiuchus until November 2001, after which it passed over the border into Sagittarius. Venus and Mercury can be found in Ophiuchus for a time each year. Shown right is an example of a star chart for Pluto in Ophiuchus in June 1999.
So why isn't Ophiucus in the Commonly-Used Western Zodiac? Ophiuchus is an Ancient Greek constellation. The Serpent Bearer is one of the original Ptolemy constellations, appearing in Al Magest Star Catalogue [c 130 - 170 AD]. He also appears on the Farnese Globe, a Roman copy of a circa 2nd century BC depiction of Atlas holding the Celestial Sphere above his head. So why isn't Ophiuchus a member of the standard astrological zodiac - the Tropical Zodiac?
