Ophiuchus

Ophiuchus depicts a healer gripping a huge serpent in both hands. It isn't one of the 12 astrological signs, yet every year from late November to mid-December the Sun really does pass through it.

How to find it

Ophiuchus is visible in the evening sky from June to September and climbs high in the south in the early evening in July. The constellation is very large, but its 2nd–3rd magnitude stars are widely scattered, so its shape can be hard to make out at first.

There are two signposts. One is the red star Antares (in Scorpius), low in the south; the other is the pair Vega and Altair, near the zenith. The wide area above Antares and to the west of Vega and Altair is Ophiuchus. Its northernmost 2nd-magnitude star is Rasalhague, the Serpent Bearer's head. Just to the west is Rasalgethi, the head star of Hercules, so the two giants appear to be standing head to head.

Connecting stars southward from Rasalhague traces a tall pentagon, or a big house with a pointed roof: the Serpent Bearer's body. On either side stretches Serpens, the Serpent, with its head to the west and its tail to the east. The Serpent Bearer's feet rest just above Scorpius, near the ecliptic.

The myth: Asclepius, god of medicine

In Greek mythology, Ophiuchus is Asclepius, god of medicine. A son of Apollo, god of the Sun and the arts, he learned the healing arts from the wise centaur Chiron. His skill grew so great that he could do more than cure the sick: he could even bring the dead back to life.

Hades, ruler of the underworld, complained that fewer souls were arriving in his realm, and Zeus also worried that the order of the world would collapse if mortals could escape death. In the end, Zeus struck Asclepius down with a thunderbolt, but in recognition of all the good he had done for people, he placed him in the sky as a constellation.

Because snakes shed their skin and seem to be reborn, they have long symbolized healing and renewal. The "Rod of Asclepius," a staff with a single snake coiled around it, is still used as a symbol of medicine, including on the flag of the World Health Organization (WHO). The serpent he holds became a separate constellation, Serpens, the only constellation split into two parts, head and tail, by another constellation, Ophiuchus.

In ancient Chinese astronomy, stars of Ophiuchus, Serpens and Hercules formed the walls of the Heavenly Market Enclosure (天市垣), a marketplace in the sky.

Main stars

Ophiuchus lies close to the direction of the Milky Way's center, so it's rich in globular clusters. All seven of its Messier objects, M9, M10, M12, M14, M19, M62 and M107, are globular clusters. North of Antares, about 460 light-years away, is the Rho Ophiuchi cloud complex, a huge cloud of gas where new stars are being born.

Birthday sign dates: why isn't it in astrology?

Ophiuchus isn't one of the 12 astrological signs, so in astrology nobody has an "Ophiuchus birthday." But every year from about November 30 to December 17, roughly 18 days, the Sun really does pass through the boundaries of Ophiuchus. That's three times longer than its stay in Scorpius just before (about 6 days). People born in this period are Sagittarius in astrology (November 22 – December 21).

The 12 astrological signs are a system that began in ancient Babylon and passed to Greece, dividing the ecliptic into twelve 30-degree slices to match the twelve months of the year. Only the feet of Ophiuchus reached the ecliptic, so it didn't make it into those twelve slots.

But in 1930, when the International Astronomical Union (IAU) set the boundaries of the 88 constellations, a section of the ecliptic officially fell inside Ophiuchus. So astronomically, the Sun passes through 13 constellations. On top of that, precession, the slow wobble of Earth's axis over about 26,000 years, moves the vernal equinox point by about 1 degree every 72 years, so over the past 2,000 years or so, astrological dates and the real sky have drifted almost a month apart. That's why news stories about a "new 13th zodiac sign" pop up from time to time.

In Planetica

Planetica places systems by the astrological sign of your birthday, so nobody's system lands in Ophiuchus because of their birthday alone. Instead, Planetica also shows the constellation the Sun was really in on your birthday as your "real sky" constellation, and if you were born between November 30 and December 17, that's where Ophiuchus appears. For example, someone born on December 5 is a Sagittarius in astrology but an Ophiuchus in the real sky.

Systems created without a birthday can also end up next to a star in Ophiuchus. The candidates are the 2,091 stars in the HYG catalog that lie within about 3,000 light-years of Earth and inside the IAU boundaries of Ophiuchus. One of them is picked at random, and the system settles about 1–6 light-years from it.

Fun facts

• The supernova that appeared in Ophiuchus in 1604 was observed in detail by Kepler and is known as "Kepler's Supernova." It's the last supernova in our own galaxy to be seen with the naked eye.
• Barnard's Star moves about 10 arcseconds across the sky each year, so in about 180 years it shifts by the width of a full Moon.

Other constellations

← ScorpiusSagittarius →

• Aries
• Taurus
• Gemini
• Cancer
• Leo
• Virgo
• Libra
• Scorpius
• Ophiuchus
• Sagittarius
• Capricornus
• Aquarius
• Pisces