In this article, we’ll be sharing with you everything you need to know about the constellation of Ophiuchus, including how to find it, deep space objects contained within it, and how to use it to find other night sky objects more easily.
The Constellation of Ophiuchus
Ophiuchus is one of the constellations that Greek astronomer Ptolemy cataloged over 2000 years ago. It was known to several ancient cultures, including the Babylonians who associated it with the serpent god Nirah.
Ophiuchus is pronounced “Oaf-ih-YOU-kus” or “off-ee-YOO-cuss” and means ‘serpent bearer’ in Greek.
The Greek myth most often associated with this constellation is that of Asclepius. Asclepius was the son of Coronis, who was either a mortal woman or a nymph, and the god Apollo.
Apollo killed Coronis because he thought she was unfaithful and gave the infant to the wise centaur Chiron to raise. Asclepius learned the art of healing from Chiron and discovered how to resurrect people by observing a living snake bringing healing herbs to a dead snake to revive it.
Hades, god of the Underworld, was concerned that souls would stop coming to the Underworld so he complained to Zeus about Asclepius. Zeus killed Asclepius with a bolt of lightning and placed him (and the Serpent) in the night sky to honor his good deeds.
To help you spot Ophiuchus, here’s what SkySafari 6 shows. Note that the snake in the picture belongs to the constellation of Serpens, which runs southwest of the snake bearer. Note the star Nunki in the Teapot of Sagittarius in the bottom left and Arcturus of Boötes in the top right of the image.
Ophiuchus has an area of 948 square degrees making it the 11th largest of the 88 recognized constellations.
Ophiuchus is usually depicted as a man holding the snake of the neighboring constellation, Serpens. In terms of bright stars, the constellation resembles a pentagon or barn silo. The Milky Way passes through Ophiuchus.
In the next section discover how to find Ophiuchus.
How To Find Ophiuchus In The Night Sky
Ophiuchus is visible to observers at latitudes between +80° and -80°. Northern Hemisphere observers can see it from May to October in the evening sky. It is best viewed on an evening in August when it dominates the mid-third of the southern sky.
Southern Hemisphere observers can see higher in the sky during winter.
The constellation of Ophiuchus is bordered by the constellations Aquila, Hercules, Libra, Sagittarius, Scorpius, and Serpens. Serpens is split into two separate sections by Ophiuchus, these are the head to the west – Serpens Caput – and the tail – Serpens Cauda.
There are a couple of ways to locate the constellation of Ophiuchus. Firstly, try using the Keystone asterism of Pegasus to point towards the brightest star of Ophiuchus, Rasalhague. A line joining the corner stars Eta Herculis and Epsilon Herculis can be extended onwards 20° to reach it. See the guide below for details.
Alternatively, do a naked-eye search for Arcturus, in Boötes. Connect a line southeastwards from there to the ‘lid’ of the Teapot asterism in Sagittarius. The bottom of Ophiuchus’s ‘barn’ lies on this line. See below for a guide.
You can measure the distances set out in degrees by using different hand shapes when held at arm’s length.
The Brightest Stars in Ophiuchus
Ophiuchus contains around 40 stars of magnitude 5.0 or brighter. The brightest star is Rasalhague, which shines at magnitude 2.1. There are another four stars brighter than magnitude 3.0, which is why this is an easier constellation to see for urban astronomy.
The more interesting stars are shown on the SkySafari 6 star chart below and, underneath that, you can find out more details about them.
Alpha Ophiuchi (Rasalhague) – This double star is the brightest in Ophiuchus. The magnitude 2.08 white giant primary and magnitude 5.00 secondary components are 0.2 arcseconds apart. We can’t see them as separate with a regular backyard telescope.
Rasalhague is one of the stars within 100 light-years of Earth, at only 47 light-years away. Its name is derived from the Arabic phrase for ‘the Head of the Serpent Collector’, which is appropriate as this star marks the top of the pentagon and represents Asclepius’s head.
Beta Ophiuchi (Cebalrai) – is an orange giant star shining at magnitude 2.76. Although cataloged as the beta star, it is actually only the fifth brightest star in Ophiuchus.
Cebalrai is 82 light-years away and marks the northeast corner of the pentagon. Its name means ‘shepherd’s dog’ in Arabic.
Gamma Ophiuchi (Muliphen) – is 103 light-years away from us. It is a white main-sequence star with a magnitude of 3.75.
Delta Ophiuchi (Yed Prior) – This is the fourth brightest star in Ophiuchus. The magnitude 2.73 orange-red giant primary and its magnitude 13.40 secondary component are 64.8 arcseconds apart.
Yed Prior is 170 light-years away and marks the southwest corner of the pentagon. ‘Yed Prior’ is derived from the Arabic for ‘leading hand’.
Epsilon Ophiuchi (Yed Posterior) – This double star is 106 light-years away. The primary shines at magnitude 3.24 and is a yellow-orange giant, the secondary is magnitude 12.27 and is 119.4 arcseconds from its companion.
Yed Posterior is also located near the southwest corner of the pentagon and ‘Yed Posterior’ is derived from the Arabic for ‘following hand’.
Zeta Ophiuchi – This magnitude 2.57 white main-sequence star is the third brightest in the constellation. It is 460 light-years away and marks the midpoint of the bottom of the ‘barn’.
Eta Ophiuchi (Sabik) – Marking the southeastern corner of the pentagon, or ‘barn’, this double star is the second brightest star in Ophiuchus, shining at magnitude 2.42. The primary star is a white main-sequence type, the secondary shines at magnitude 3.27 and is 0.4 arcseconds away. These are too close to be split in a backyard telescope.
Sabik is 88 light-years away and its name refers to the one that ‘precedes’ or ‘comes first in Arabic.
Theta Ophiuchi – South of Sabik, this variable double star is 436 light-years away. The magnitude 3.25 blue-white subgiant primary and magnitude 6.20 secondary components are 0.1 arcseconds apart.
The primary is a pulsating variable star ranging in magnitude from 3.25 to 3.31 with a period of 0.14 days (three hours and 22 minutes).
Kappa Ophiuchi – Marking the northwest corner of the pentagon, this magnitude 3.19 orange giant variable star is 91 light-years away. It’s a pulsating variable ranging in magnitude from 4.10 to 5.00.
Iota Ophiuchi – One degree northwest of Kappa Oph. this star shines at magnitude 4.36. It is a blue-white main-sequence star that is 245 light-years away from us.
Lambda Ophiuchi (Marfik) – This variable double star is 173 light-years away. The primary is a magnitude 3.90 white main-sequence star, while the secondary is 1.4 arcseconds away and shines at magnitude 5.15 magnitude.
Marfik means ‘elbow’ in Arabic.
Mu Ophiuchi – This magnitude 4.61 white giant is 750 light-years away. Its mass is 7.0 Solar masses, its diameter is 6.6 Solar diameters, and it is 2.6 times hotter than the Sun.
Nu Ophiuchi (Sinistra) – This magnitude 3.31 orange giant star is 151 light-years away. Its mass is about the same as the sun’s but its diameter is 16.5 times larger. Sinistra means ‘the left side’ in Latin.
Xi Ophiuchi – This double star is 57 light-years away. The yellow-white giant primary shines at magnitude 4.38, the secondary star is 3.5 arcseconds away and shines at magnitude 8.89 magnitude. This may be a multiple system.
Rho Ophiuchi – Only just inside the boundary with Scorpius, this double star is 360 light-years away. The magnitude 4.57 yellow-white subgiant primary and magnitude 5.74 magnitude main-sequence, secondary components are 2.8 arcseconds apart.
Sigma Ophiuchi – Inside the northeastern end of the pentagon, this magnitude 4.32 bright orange giant is 900 light-years away, making it one of the most distant bright stars in the constellation.
It is a huge star with a diameter 77 times larger than the sun’s. However, it has the same mass as our star and is 24% cooler than the Sun.
Tau Ophiuchi – Practically part of the tail of Serpens, this double star is 167 light-years away. The two stars in the system shine at magnitude 4.76 and 5.86 and are only 1.5 arcseconds apart. The primary is a yellow-white main-sequence star.
Upsilon Ophiuchi – Three degrees northwest of Zeta Oph. is this double star, which is 134 light-years away.
The magnitude 4.63 yellow-white primary and its magnitude 8.85 secondary component are a huge 776.2 arcseconds (almost 13 arcminutes) apart.
Phi Ophiuchi – This double star is 244 light-years away. The two components are 41.3 arcseconds apart and shine at magnitude 4.28 (the yellow-orange primary) and 12.90.
Chi Ophiuchi – Just missing out on being a star in Scorpius, this magnitude 4.26 yellow-white giant is 525 light-years away. It’s an eruptive variable whose magnitude ranges from 4.17 to 5.00.
Psi Ophiuchi – Also skirting incredibly close to Scorpius is this magnitude 4.48 orange giant. It is 199 light-years away and has a similar mass to the sun. Its diameter is equivalent to 13.4 solar diameters but the star is 19% cooler than the sun.
Omega Ophiuchi – This magnitude 4.44 white main-sequence star is 169 light-years away. It’s a rotating variable whose magnitude ranges from 4.44 to 4.51 over 2.99 days.
36 Ophiuchi – This is a triple star system just 19.5 light-years away from Earth. The magnitude 4.32 yellow-orange main-sequence primary and magnitude 4.33 yellow-orange dwarf secondary components are 5.1 arcseconds apart.
The third component, an orange-red dwarf, is 700 arcseconds away from the primary and secondary.
51 Ophiuchi – This magnitude 4.80 white main-sequence star is 406 light-years away. It is 3.3 times greater than the sun’s, its diameter is equivalent to 4.6 solar diameters, and it is 1.8 times hotter than our local star.
67 Ophiuchi – This double star is 1200 light-years away from our solar system. The magnitude 3.98 blue-white supergiant primary and magnitude 13.70 secondary components are 6.7 arcseconds apart. This may be a multiple-star system.
Star Hopping From Ophiuchus
Ophiuchus is the starting point for three well-known star hops that land at Messier objects. Star hopping is the process of using brighter objects, such as obvious stars in constellations, to find fainter ones that can’t be seen with the naked eye. Find out more about star hopping (opens a new tab).
M9 – Identify Sabik at the southeast corner of Ophiuchus’s pentagon. The globular cluster, M9, is about 3.5° southeast of the star.
M10 & M12 – These two globular clusters are both inside the pentagon of Ophiuchus.
To find them, draw an imaginary line from Zeta Ophiuchi to Yed Prior (~9°) then imagine it’s the base of a right angle triangle ~9° tall and extending toward the center of Ophiuchus.
The magnitude 4.8 star, Ophiuchi 30, is at the third corner of this triangle. M10 is ~1° west of Ophiuchi 30 and M12 is ~3° northwest of M10.
M14 – This is also a globular cluster. We can find it by drawing an imaginary line between Gamma Ophiuchi and Sabik (~20°). Magnitude 4.61 Mu Ophiuchi and magnitude 4.63 HR 6493 are near the midpoint of this line.
Draw an imaginary line between them (~4°) then imagine it’s the base of a triangle ~3° tall and pointing toward Gamma Ophiuchi. M14 is at the third corner of this triangle.
Objects To See Within Ophiuchus
Ophiuchus contains seven Messier objects and some other deep sky objects suitable for small telescope users.
Most of these objects are globular clusters and the reason there are so many is that we are looking out into the plane of the Milky Way when we look at Ophiuchus. The density of stars, and clusters, in particular, is much higher in this direction.
M9 (NGC 6333)– This globular cluster has a magnitude of 7.71 and an apparent size of 12.0 arcminutes. It’s 26,000 light-years away and is at right ascension 17h 19m 11s and declination -18° 30’ 57” (J2000.0).
M10 (NGC 6254)– This globular cluster has a magnitude of 6.59 and an apparent size of 20.0 arcminutes. It’s 14,300 light-years away and is at right ascension 16h 57m 27s and declination -04° 06’ 01”.
M12 (NGC 6218)– This globular cluster has a magnitude of 6.69 and an apparent size of 16.0 arcminutes. It’s 16,000 light-years away and is at right ascension 16h 47m 14s and declination -01° 56’ 58”.
M14 (NGC 6402)– This globular cluster has a magnitude of 7.59 and an apparent size of 11.0 arcminutes. It’s 30,000 light-years away and is at right ascension 17h 37m 36s and declination -03° 14’ 45”.
M19 (NGC 6273)– This globular cluster has a magnitude of 6.76 and an apparent size of 17.0 arcminutes. It’s 29,000 light-years away and is at right ascension 17h 02m 38s and declination -26° 16’ 04”.
M62 (NGC 6266)– This globular cluster has a magnitude of 6.44 and an apparent size of 15.0 arcminutes. It’s 22,000 light-years away and is at right ascension 17h 01m 13s and declination -30° 06’ 49”.
M107 (NGC 6171)– This globular cluster has a magnitude of 7.92 and an apparent size of 13.0 arcminutes. It’s 21,000 light-years away and is at right ascension 16h 32m 32s and declination -13° 03’ 14”.
NGC 6304– This globular cluster has a magnitude of 8.22 and an apparent size of 8.0 arcminutes. It’s 19,000 light-years away and is at right ascension 17h 14m 32s and declination -29° 27’ 43”.
NGC 6572– This planetary nebula has a magnitude of 8.00 and an apparent size of 0.3 x 0.2 arcminutes. It’s 2,600 light-years away and is at right ascension 18h 12m 07s and declination -06° 51’ 25”.
NGC 6633– This open cluster has a magnitude of 4.59 and an apparent size of 20.0 arcminutes. It’s 1,226 light-years away and is at right ascension 18h 27m 15s and declination +06° 30’ 00”.
IC 4665– This open cluster has a magnitude of 4.19 and an apparent size of 70.0 arcminutes. It’s 1,100 light-years away and is at right ascension 17h 46m 18s and declination -05° 43’ 00”.
Barnard 59 (Pipe Nebula)– This dark nebula has an apparent size of 50.0 x 50.0 arcminutes. It’s ~450 light-years away and is at right ascension 17h 11m 07s and declination -27° 23’ 38”
Barnard 68– This dark nebula has an apparent size of 5.0 x 3.0 arcminutes. It’s 522 light-years away and is at right ascension 17h 22m 39s and declination -23° 50’ 04”.
Barnard 72 (Snake Nebula)– This dark nebula has an apparent size of 27.0 x 15.0 arcminutes. It’s 650 light-years away and is at right ascension 17h 23m 38s and declination -23° 35’ 30”.
Rho Ophiuchus Dark Nebula Complex (IREC 500)– This dark nebula has an apparent size of 670.0 x 230.0 arcminutes. It’s 391 light-years away and is at right ascension 16h 32m 30s and declination -24° 05’ 00”.
Rho Ophiuchus Nebula Complex (IC 4604)– This bright nebula has a magnitude of 5.09 and an apparent size of 60.0 x 25.0 arcminutes. It’s 390 light-years away and is at right ascension 16h 25m 36s and declination -23° 26’ 00”.
Ophiuchus is a large, pentagon-shaped constellation that lies on the line of the ecliptic – which should make it a zodiac constellation, but it in face belongs to the Hercules family.
The stars of Ophiuchus lay in the direction of the plane of our galaxy, the Milky Way, which makes it rich with star clusters and dark nebula.
Enjoy exploring its many wonders this summer.
Written by Tanya C. Forde