The constellation Ophiuchus contains seven globular clusters with Messier designations, including this one, M9. Credit: AURA/NSF/NOAO
Summer is drawing to a close here in the Northern Hemisphere, and with it the summer constellations are disappearing from view. Ophiuchus is one of the constellations setting in the southwestern sky: Get out and observe it while you can.
Ophiuchus is a unique constellation in that it lies in the plane of the ecliptic, yet it is not counted as one of the traditional zodiacal constellations. Ophiuchus lies between Sagittarius to its lower left with its telltale teapot shape, and the curving form of Scorpius with its bright and reddish star Antares, which lies below and to the right of Ophiuchus.
The constellation of Ophiuchus is supposed to represent a serpent bearer. The snake that Ophiuchus is holding lies on either side of him and is named Serpens. The main stars in Ophiuchus range from magnitude 2.0 to 3.3, and the nine brightest form a difficult-to-decipher form of a man with his legs toward the southern horizon.
Because of Ophiuchus’s location along the edge of the Milky Way and near the center of the galaxy (which is located in the direction of its neighbor Sagittarius), it contains a large number of globular clusters. Globular clusters are massive groupings of stars, like miniature satellite galaxies, that orbit around the core of the galaxy. The Milky Way has more than 100 globular clusters located in its halo that formed along with its parent galaxy; thus, globular clusters are some of the oldest stars that can be observed. Stars in globular clusters are called Population II stars and have very low amounts of metal.
The seven globular clusters named by Charles Messier in Ophiuchus are:
All the globular clusters are between magnitudes 6.6 and 8.1, which should be within reach of binoculars or a small telescope from a dark-sky site.
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