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Ophiuchus (known as the serpent holder) is one of the 88 constellations, and was also one of the 48 listed by Ptolemy. Of the 13 zodiac constellations (constellations that can contain the Sun during the course of a year), Ophiuchus is the only one which is not counted as an astrological sign - see below for more information.
Ophiuchus is depicted as a man supporting a snake, Serpens; the interposition of his body divides the snake into two parts, Serpens Caput and Serpens Cauda, which are nonetheless counted as one constellation.
The brightest stars in Ophiuchus include α Ophiuchi, called Rasalhague, at the figure's head; and λ Ophiuchi, a triple star, at his elbow.
RS Ophiuchi, a star too faint to interest amateur skywatchers, is part of a strange class called recurrent novas, whose brightness increases at irregular intervals by hundreds of times in a period of just a few days.
Notable deep-sky objects
Ophiuchus contains several star clusters, such as IC 4665, NGC 6633 , M9, M10, M12, M14, M19, M62, and M107, as well as the nebula IC 4603-4604 . The unusual double galaxy NGC 6240 is also in Ophiuchus.
The figure is supposed to represent the legendary physician Asclepius, who learned the secrets of life and death from one serpent bringing another some herbs which healed it (Asclepius had previously tried to kill it). In order to avoid the human race becoming immortal under Asclepius's care, Zeus eventually killed him with a bolt of lightning, but placed him in the heavens to honour his good works. The involvement in the myth of Chiron may be connected to the nearby presence of the constellation Sagittarius, which was in later times occasionally considered to represent Chiron (who was more usually identified as the constellation Centaurus).
It is not, however, easy to find the figure of a man in these stars without some diligence, since Ophiucius is intersected by Serpens, parts of which some people identify as the base of Ophiucius' torso (making identification of other parts quite difficult), rather than a snake below it.
This constellation, known from antiquity, is one of the 48 constellations described by Ptolemy. It has also been known as Serpentarius, a Latin form of its name.
The most important historical event in Ophiuchus was the Supernova 1604, also named Kepler's Supernova, whose explosion was first observerd on October 9, 1604, near θ Ophiuchi. Johannes Kepler saw it first on October 16, but studied it so extensively that the supernova was subsequently named after him. He published his findings in a book entitled De stella nova in pede Serpentarii (On the New Star in Ophiuchus's Foot). Galileo used its brief appearance to counter the Aristotelian dogma that the heavens are changeless.
It occurred only 32 years after another supernova in Cassiopeia that had been observed by Tycho Brahe; the last supernova before then had occurred in 1054 (see Crab Nebula), and after Kepler's no further supernovae were observed until 1987 (see Supernova 1987a.)
In the 2nd century, Ptolemy listed 29 stars in Ophiuchus. He recognised that most of those stars were north of the ecliptic (the path of the Sun through the sky) - however, 4 of them (today known as 36 Oph, 42 θ Oph, 44 Oph and 51 Oph) he recognised as being south of the ecliptic. Therefore, the Sun passed through the constellation of Ophiuchus as it was recognised by Ptolemy. Many astrologers (incorrectly) state that the phenomenon of the Sun passing through Ophiuchus dates from a decision by the International Astronomical Union to adopt constellation boundaries in 1930 - in fact, the phenomenon predates that decision by over 1,700 years.
The reason why Ophiuchus isn't a part of the western astrological zodiac is because that zodiac is defined on the basis of the sun spending an equal amount of time in twelve astrological signs starting at the vernal equinox - this is called the tropical zodiac. There is also, for instance, a sidereal zodiac, which is based on the actual location of the stars in the sky.
- Ophiuchus the Zodiac Sign this is a pro-astrology link
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