Ophiuchus, The 13th Zodiac Sign

Image Credit: Wikimedia Commons

The constellation Ophiuchus is Greek for ‘serpent-bearer’ and is depicted as a man grasping a snake, represented by the nearby constellation of Serpens. It is sometimes known as the Zodiac’s 13th or forgotten constellation as together with the other 12 zodiac constellations, it lies on the ecliptic, or the imaginary circle that marks the Sun’s annual path through the sky. Ophiuchus’ brightest star is a blue giant called Rasalhague, which is 47 light years away, and shines with a magnitude of 2.07.


Ophiuchus is a southern sky constellation, that can be seen by observers located between +80° and -80° of latitude. The constellation is the night sky’s 11th largest, and can be found between Scorpius and Sagittarius, where it takes up 19 degrees worth of the ecliptic.  Other neighbouring constellations include Aquila, Hercules, Libra, and Serpens.

Hercules Constellation Family

Ophiuchus is a member of the Hercules family of constellations, together with Aquila, Ara, Centaurus, Corona Australis, Corvus, Crater, Crux, Cygnus, Hercules, Hydra, Lupus, Lyra, Sagitta, Scutum, Sextans, Serpens, Triangulum Australe and Vulpecula.

The Forgotten Zodiac Sign

Ophiuchus, The 13th Zodiac Sign

Despite the fact that between November 30th to December 17th, the Sun spends around nineteen days of the year in Ophiuchus, astrologers haven’t formerly accepted the constellation into their wheel of zodiacal signs. A possible explanation for its omission is that when the zodiacal signs were introduced in Mesopotamia between 3,200 and 500 BC, the 360 degree sky was divided neatly up into 12 equal parts of 30 degrees widths. Since the idea of 12 zodiac signs ruling over 12 months was much more appealing for early astrologers, they still use the system today, despite Ophiuchus’ being included in Ptolemy’s Almagest around 150 AD.

Principal Stars

– Rasalhague (Alpha Ophiuchi), the constellation’s brightest star, is actually a binary system consisting of a white giant (A5 III) being orbitted by an orange main sequence dwarf (K5-7 V) once every 8.62 years. The system is 47 light years from Earth, and shines with a combined visual magnitude of 2.07.

Image Credit: Mike Simonsen

– Sabik (Eta Ophiuchi), the second brightest star in Ophiuchus, is found 88 light years from our solar system and shines with a magnitude of 2.43. It is, however, a binary star system consisting of two white main sequence dwarfs with an orbital period of 87.58 years.

– Zeta Ophiuchi, the constellation’s third brightest star, is a blue main sequence star situated 366 light years distant of magnitude 2.569. This Beta Cephei variable star is around 3 million year’s old, and has 8 times our Sun’s radius, and 19 times its mass. It also spins at an incredibly fast rate of 400 km/s.

Other stellar objects of interest in Ophiuchus includes Barnard’s Star, a red dwarf (M4Ve) found just 6 light years away, making it the 4th nearest star to our own solar system, with only the Alpha Centauri system consisting of Alpha Centauri A (4.3ly), Alpha Centauri B (4.3ly), and Proxima Centauri (4.2ly) closer. Ophiuchus also includes the blue-white supergiant 67 Ophiuchi; the white main sequence dwarf Gamma Ophiuchi; the yellow giant star Yed Posterior (Epsilon Ophiuchi); the orange giant stars Celbalrai (Beta Ophiuchi) and Sinistra (Nu Ophiuchi); the red giant Yed Prior (Delta Ophiuchi); and the red dwarfs GJ 1214 and Wolf 1061.

Notable Deep Sky Objects

Ophiuchus contains an impressive seven Messier objects, which are all globular cluster situated between 14,300 and 30,300 light years from Earth. These include M9, M10, M12, M14, M19, M62, and M107. It also contains NGC 6240, an ultraluminous infrared galaxy; as well as several colorfully named nebulae, such as the Dark Horse Nebula, Little Ghost Nebula, Snake Nebula, Pipe Nebula, and the Twin Jet Nebula.

The well documented supernova explosion of 1604 was observed by Johannes Kepler in the constellation of Ophiuchus, and was later used by Galileo to counter the Aristotelian dogma of the changeless nature of the heavens. Kepler’s Supernova took place 20,000 light-years away, and at magnitude −2.5 was seen during the day for almost one month.

The Mythology

OphiuchusThe 13th constellation on the zodiac belt Ophiuchus, honours the ancient medical healer known by the Ancient Greeks as ‘Aesclepius’ and Egyptians as Imhotep. Aesclepius, the son of Apollo and the mortal princess Coronis, was raised and mentored by the centaur Chiron, who instructed him in the art of medicine. In time, Aesclepius became famous as a miracle-working medicine man, and was later given a magical healing potion by the goddess Athena made from the blood of the snake-haired Gorgon. However, Aesclepius offended Zeus by using the potion to raise the dead for money, and therby upsetting the natural order of the universe. He was subsequently killed by a thunderbolt from Zeus, who later acknowledged the good Asclepius had achieved during his life, and so placed him among the stars as the constellation Ophiuchus.

Today, the symbol for the field of medicine is depicted by Aesclepius’ snake-entwined staff  although a staff with two snakes known as a caduceus, is sometimes mistakenly used instead. The origin of the ancient serpent and rod symbol probably relates to the practice used at the time by physicians, for curing infection by “guinea worm,” or Dracunculus medinensis. The filarial worm would crawl around under the skin of the victim’s body,  but could be removed by the physician by cutting a slit in its path, before carefully winding the worm around a stick until the pest had been removed. It is believed that a sign with the worm on a stick is how physicians advertised their services at the time. Interestingly, Ophiophobia is the name used to describe the fear of snakes or other reptiles.

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