M9 is a globular cluster located in the southern section of the large sprawling constellation of Ophiuchus. It was discovered by Charles Messier on May 28, 1764, who described it as a "nebula without star of 3 arc minutes in diameter". With an apparent magnitude of +8.4, it's one of the fainter objects of its type in Messier's catalogue. Since not particularly bright, M9 is a challenging object for binocular observers appearing at best as a slightly out of focus faint "star" that can be difficult to pick out against the surrounding Milky Way. The cluster is much easier to spot with larger 15x70 or 20x80 binoculars, but again not much detail is discernible.
M9 is located 25,800 light-years from Earth. At a distance of 5,500 light-years, it's one of the nearer globular clusters to the center of the Milky Way Galaxy. The globular lies adjacent to a prominent dark nebula called Barnard 64, which significantly dims the light of the cluster due to intervening interstellar dust.
To find M9 start by locating Sabik (η Oph - mag. +2.4) the second brightest star in Ophiuchus. About 3 degrees southeast of Sabik is M9, which is best seen during the months of May, June and July.
When viewed through a small 80mm (3.1-inch) telescope, M9 appears as a small faint diffuse non-stellar patch of light. Even at high magnifications the cluster is not resolvable. A 200mm (8-inch) scope displays a concentrated core about 8 arc minutes in diameter surrounded by a small faint halo. At best a few stars are resolved around the edges, especially when using averted vision. Large amateur telescopes of aperture 300mm (12-inch) or greater resolve the cluster much better. Observers may be able to notice that M9 appears slightly flattened due to the gravitational pull of our own galactic core. The brightest member stars are about mag. +13.5.
In total, M9 has an apparent diameter of 12 arc minutes, which corresponds to an actual diameter of 90 light-years. It's estimated to be 12 billion years old and contains at least 100,000 stars. The globular is receding from us at a speed of 224 km/sec.
M9 Data Table
|Object Type||Globular cluster|
|RA (J2000)||17h 19m 12s|
|DEC (J2000)||-18d 30m 59s|
|Apparent Size (arc mins)||12 x 12|
|Age (years)||12 Billion|
|Number of Stars||>100,000|
|Notable Feature||One of the closest globular clusters to the centre of the Milky Way|