Ophiuchus

The Serpent Holder

GenitiveOphiuchi
AbbreviationOph
Right Ascension15h58 to 18h42
Declination+14.3° to -30.1°
Area (sq deg)948
Brightest StarRas Alhague
Optimum VisibilityJune
Map of Ophiuchus
Relative Galactic Position of Ophiuchus

In combination with its neighbour Sagittarius, the constellation of Ophiuchus encloses the central regions of our Milky Way Galaxy.

Derivation

The group of stars has been known by the name Ophiuchus for two thousand years or more. What is not known, though, is why the name 'Serpent Holder' was assigned to them. Some suggest that the constellation represents Asclepius or Aesculapius, the healer of Greek myth whose cult was closely associated with serpents. This identification is by no means certain.

Stars

Ophiuchus is a large constellation (the eleventh largest in the sky), and contains a number of bright stars. The star designated Alpha Ophiuchi is Ras Alhague, a fairly nearby star with a name that means 'Head of the Serpent Holder'. There are four other stars above third magnitude: in descending order of brightness, these are Sabik, Zeta Ophiuchi, Yed Prior and Kelb Alrai.

More famous than any of these is Barnard's Star, which lies just under six light years from Earth, and is one of the Sun's closest neighbours. It is a very small and faint red star of the type known as subdwarfs, so that despite being so nearby, it is invisible to the naked eye.

Star Clusters

Ophiuchus abounds with Globular Clusters, and though none can be seen with the naked eye, Messier 10 is quite easy to make out with even a small telescope. Other similar star clusters in this constellation are M12, M19, M62 and M107.

These Globular Clusters are very distant objects, with the nearest (M10) being more than 14,000 light years from Earth. Nearer to home, at just 1,000 light years, a bright open cluster can be seen near Ophiuchus' border with Serpens Cauda. This is NGC 6633.

The Thirteenth Sign of the Zodiac

When the zodiac was first delineated by the ancients, it consisted of twelve 'houses', each associated with one of twelve constellations that lay along the Ecliptic: Aries, Taurus, Gemini, Cancer, and so on. Since that time, gravitational effects on the orbit of the Earth, known as 'precession', have caused the line of the Ecliptic to change slightly. Specifically, it now passes through thirteen constellations, with Ophiuchus being the new addition. Where the Sun once passed directly from Scorpius into Sagittarius, it now spends nineteen days each year, from 30 November to 18 December, in the new 'house' of the Serpent Holder.

Indexes

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