Credits: NASA & ESA
M9 (also designated NGC 6333) is a globular cluster in the constellation of Ophiuchus.
It is positioned in the southern part of the constellation to the southwest of Eta Ophiuchi, and lies atop a dark cloud of dust designated Barnard 64.
The cluster was discovered by French astronomer Charles Messier on June 3, 1764, who described it as a "nebula without stars".
In 1783, English astronomer William Herschel was able to use his reflector to resolve individual stars within the cluster.
He found the cluster to be 7−8′ in diameter with stars densely packed near the centre.
M9 has an apparent magnitude of 7.9, an angular size of 9.3′, and can be viewed with a small telescope. It is one of the nearer globular clusters to the center of the Milky Way Galaxy with a separation of around 5,500 light-years from the Galactic Core. Its distance from Earth is 25,800 light-years.
The total luminosity of this cluster is around 120,000 times that of the Sun, the absolute magnitude being -8.04. The brightest individual stars in M9 are of apparent magnitude 13.5, making them visible in moderately sized telescopes.
Facts about M9 by Keith Turnecliff
Located only 25,000 light-years away in the constellation Ophiuchus, M9 is one of the closest globular clusters to the center of our Milky Way galaxy.
The stars in the globular cluster are gravitationally bound to each other, with most of the stars concentrated at the cluster’s center.
This large central mass pulls outer stars inward and causes globular clusters to have a spherical shape.
M9’s proximity to the much greater mass at the center of the Milky Way has warped the cluster’s shape, though, so it appears less spherical than other objects of its kind.
M9 was discovered by Charles Messier in 1764. It has an apparent magnitude of 8.4 and can be observed using a small telescope. The best time of year to spot the cluster is during the month of July.
This Hubble image of M9’s core was created from exposures taken in visible, infrared and ultraviolet light. The stars in the image have different colors based on their properties. Red stars have lower surface temperatures, while blue stars are extremely hot.