Ophiuchus

by Tammy Plotner on December 12, 2008

Ophiuchus

Ophiuchus

The sprawling constellation of Ophiuchus sits on the celestial equator and was one of the 48 original constellations charted by Ptolemy and later adopted by the IAU. Of the 13 zodiacal constellations (constellations through which the Sun passes during the course of the year), Ophiuchus is the only one not designated as an astrological sign. It covers 948 square degrees of sky and ranks 11th in size. Ophiuchus contains 10 main stars in its asterism and has 62 Bayer Flamsteed designated stars within its confines. Ophiuchus is bordered by the constellations of Hercules, Serpens Caput, Libra, Scorpius, Sagittarius, Serpens Cauda and Aquila. It is visible to all observers at latitudes between +80° and ?80° and is best seen at culmination during the month of July.

There is one well documented annual meteor shower associated with the constellation of Ophiuchus which peaks on or about June 20 of each year – the Ophiuchids. The radiant – or point of origin – for this meteor shower is near Sagittarius border. The fall rate varies from average 8 to 20 meteors per hour, with occasionally many more. Watching on a Moonless night when the constellation is at its highest will greatly improve the amount of meteors you see!

At one time, the constellation of Ophiuchus was referred to as “Serpentarius”, whose name literally meant the “serpent bearer”. In most mythology representations, you’ll see Ophiuchus represented as a man grappling with a large snake; his body representing the division of the snake “Serpens” into two parts – Serpens Caput and Serpens Cauda. Even though divided by Ophiuchus, they still are only one constellation. It is possible the mythological figure could represent the healer Asclepius, placed close to Chirion (Sagittarius), his mentor. The man could also be the Trojan priest Laocoön, who was killed by a pair of sea serpents after warning about the Trojan Horse. It could even be Apollo wrestling with the Python to take control of the oracle at Delphi…. But no matter which figure you choose, this huge constellation holds a vast number of deep sky riches just waiting to be explored!

Let’s begin our binocular tour of Ophiuchus with its brightest star – Alpha – the “a” symbol on our map. Located about 47 light years distant from Earth, Rasalhague is an A-type giant star that’s recently exhausted its core hydrogen reserves. But, “the Head of the Serpent Collector” isn’t alone, but Rasalhague is a binary star. Power up in a telescope to look for a faint, very close companion only 0.5″ away.

Head on next to Beta Ophiuchi, the “B” symbol on our map. This K-type giant star is located about 82 light years from our solar system and its proper name is Cheleb. Also known as 44 Oph, we have something of a mystery star here. Precise radial velocity measurements taken over 8 consecutive nights in 1992 June and 2 nights in 1989 July revealed the presence of a 0.255 +/- 0.005 day period. A pulsing variable star! It’s easy to catch in binoculars, but you might want a telescope for what’s nearby…

It’s called Barnard’s Star and found due east of Beta (RA 17:57:48.5 Dec +04:41:36). Located approximately 6 light-years away from, Barnard’s Star is a very low-mass red dwarf star. In 1916, American astronomer E. E. Barnard measured its proper motion as 10.3 arc seconds per year, which remains the largest known proper motion of any star relative to the Sun. Even though it’s an ancient star at 7 to 12 billion years old, there are still possibilities of flare events – such as one that occurred in 1998. The flare was surprising because intense stellar activity is not expected around stars of such age.

Now have a look at Eta Ophiuchi – the “n” symbol on our map. This time you’ll want a telescope because Sabik is a difficult to split binary star system. Here we have two fairly unremarkable A class main sequence stars – close to equal in magnitude and not anything special if taken apart. However, together the Eta binary is strange because they orbit around a common center in a very fast and highly elliptical path.

Now put your binoculars on Deta – the “8” symbol on our map. Known as Yed Prior, you’ll quickly notice it is an optical double star with Epsilon whose name is Yed Posterior. Delta Ophiuchi is a red giant star located 170 light years from our solar system, while Epsilon is 108 light years away and a G-class giant star. These two are important, because they’ll guide you to our next two objects to the east.

For binoculars and telescopes, it’s time to enjoy some of Ophicuhus many Messier Catalog riches and we star with the giant globular clusters, M10 and M12. You’ll find Messier 10 located at RA 18:57:0 Dec -04:05:57. Discovered by Charles Messier on May 29, 1764 this awesome globular cluster hangs out about 4,300 light-years and spans about 23 light years of space. You can see it easily in binoculars, but it will require a telescope to begin resolving stars. Nearby, Messier 12 (RA 10:47:14 Dec -01:58:52) is also an all instruments type of globular cluster, but with a much looser structure. Why? A study published in 2006 revealed that M12 may have lost as many as one million of its low mass stars to the gravitational influence of the Milky Way!

Large telescopes will love Messier 19 (RA 17:02.6 Dec -26:16). It’s one of the most oblate globular clusters in the sky and thanks to the work of Harlow Shapely, we’ve learned to take a better look, because he estimated there are twice as many stars along M19’s major axis than along its minor. This rich, dense globular cluster was one of Charles Messier’s original discoveries, but Sir William Herschel was the one to resolve it into “countless stars of mag 14, 15, 16″.

Try your hand with Messier 107 (RA 16:32.5 Dec -13:03). This 20,000 light year distant globular cluster is full, too! Discovered by Pierre Méchain in April, 1782 and later added to Messier’s catalog by Helen Sayer Hogg, this one is also a resolution delight in larger telescopes. Look for some dark obscured regions. According to SEDS: the star distribution is called “very open” by Kenneth Glyn Jones, who points out that this cluster “enables the interstellar regions to be examined more easily, and globular clusters are important `laboratories’ in which to study the process by which galaxies evolve.”

Don’t forget Messier 63 (RA 17:01.2 Dec -30:07)! It’s another globular cluster whose distortion by our own Milky Way’s influences are easily apparent in a telescope. Thanks to studies by the Chandra X-Ray Observatory, we know it contains a large number of X-ray binaries, proving that M63 has undergone core collapse.

How about Messier 14 (RA 17:37:36.1 Dec -03:14:45). Spanning across 101 light years of space and located about 30,000 light years away, this magnificent globular cluster is often overlooked. Discovered by Charles Messier on June 1, 1764, this bright ball of stars is near magnitude 7 and well within range of binoculars and small telescopes. M14 had a nova occur in 1948, but it wasn’t discovered until 1964 when the photographic plates were being surveyed. It wasn’t done with surprises either… In an area where all stars should be about the same age, a carbon star was discovered in 1997!

For challenging large telescope studies, take a look at three planetary nebulae. NGC 6309 (RA 17:14.1 Dec -12:55) is often referred to as the “Box Nebula”, for its unique structure. Far brighter NGC 6572 (RA 18:12.1 Dec +06:51) has the wonderful nickname of the “Blue Racquetball”. In his observing notes, Walter Scott Houston writes: Walter Scott Houston wrote, “My old 10-inch reflector showed the vivid green color of the object with any power more than 50x. It is interesting to note that older observers have described NGC 6572 as green, while the younger ones tend to call it vivid blue.”. I see blue… Do you? And don’t forget to try NGC 6369 (RA 17:29:20.4 Dec -23:45:35)… the “Little Ghost” is a seasonal favorite!

There’s many, many more wonderful objects just waiting in Ophiuchus for you to explore. Be sure to get a good star chart and you’ll see why the “Serpent Bearer” still stands grasping the stars… There’s so much to do!

Sources:
SEDS
Chandra Observatory
Chart Courtesy of Your Sky.

About 

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

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