Ophiuchus is usually associated with Asclepius, in Greek mythology son of Apollo and god of medicine. The attribute of Asclepius was the snake, a symbol of rejuvenescence because the snake sloughing his skin was thought to renew his youth. Asclepius was slain by Zeus with a thunderbolt and turned into Ophiuchus the snake-holder where he holds the serpents /constellations “Serpens Cauda” to the east and Serpens Caput to the west.
Pluto at magnitude 13.8 is currently on the southern border of Serpens Cauda and Ophiuchus.
Ophiuchus is one of the large constellations currently in our Northern sky. The southern region of the constellation marks the direction of the Galactic Centre towards which globular clusters tend to concentrate. Therefore Ophiuchus has at least 20 globular star clusters, more than any other constellation.
The globulars M 9, 10, 12, 14, 19, 62 and 107 should all be faintly visible in a dark sky with binoculars. However a 150mm to 200 telescope will make observations more interesting.
M10 and M12 with 3° 16’ angular separation are easily located in the central portion of the constellation (see map).
M10 magnitude 6.6, size 15.10’, 14,000 ly away is brighter, more dense and easily resolved with my 128 mm scope.
M12 mag 6.6, size 14.50’ , 18,000 ly away, was fainter and more loosely scattered.
Take time to compare these with M4 near Antares in Scorpius.
M 19 is more oval and M 62 has an irregular outline.
How many globular clusters can you find in Ophiuchus?
The brightest star α (alpha) Ophiuchi, mag 2.1, marks the head of the serpent holder.
The most celebrated star in the constellation is Barnard’s Star discovered by E.E. Barnard in 1916. Only 6 ly away it is the nearest star after Alpha Centrauri. It is a 9.5 magnitude red dwarf star which has the greatest proper motion (apparent motion across the sky) of any known star, 10.4 arc seconds per year.
RS Oph usually around 12 th mag is a recurrent nova. It has flared up to naked eye brightness in 1898, 1933, 1958, 1967 and 1985.
Sydney amateur astronomer Peter Williams discovered another nova, Nova Ophiuchi 2006 No. 2 in April this year on the southern border of the constellation near the globular cluster NGC 6304.
(Notes on novas and supernovas: a nova is an existing star, usually quite faint whose brightness suddenly increases by 10 magnitudes or more then slowly returns to pre- nova state. Novae occur in close binary systems where one component is a white dwarf and the other a giant. Matter drains from the surface of the giant where gravity is weak and to the surface of the white dwarf, where gravity is strong. Nuclear reactions involving the infalling material cause a violent explosion on the surface of the white dwarf. The energy of the explosion is about the same as the sun emits in 10,000 years.
A supernova is a stellar explosion where almost an entire star is disrupted. A supernova is 1000 times brighter than a nova and may outshine all other stars in the galaxy for a week or more).