Degree of difficulty 3 (of 5)

Minimum aperture 30mm

Designation NGC 6402

Type Globular cluster

Class VIII

Distance 55,620 ly (R2005)

Size 180 ly

Constellation Ophiuchus

R.A. 17h 37.6min

Decl. −3° 15′

Magnitude 7.6

Surface brightness –

Apparent diameter 11′

Discoverer Messier, 1764

History M 14 was discovered by Charles Messier on the 1st of June 1764, within days of finding its neighbors and fellow globular clusters M 9, M 10, and M 12. Messier wrote: “Nebula without star; the nebula is not large, its light is faint, it is round. Near it is a small star of the 9th magnitude; 7′ diameter.” By contrast, 19 years later, William Herschel found M 14 “extremely bright, easily resolvable” and wrote: “With 300× I can see the stars. The cluster is considerably behind the scattered stars, as some of them are projected upon it.” For John Herschel, too, M 14 was “a striking object.” In 1833 he noted: “Very large; 8′ or 10′ diameter; the stars so excessively minute as to be scarcely discernible.” Admiral Smyth described a “lucid white color.” Heinrich d'Arrest saw M 14 as “elegant, comet-like, almost round, irregularly terminated, resolved with 226×.”

Astrophysics While M 14 appears over a magnitude fainter than its neighbors M 10 and M 12, and is on a par with M 9, it is in fact the most luminous of these four globular clusters in Ophiuchus, in absolute terms. M 14 suffers as much as two magnitudes of extinction due to its much greater distance and interstellar absorption by dust in the Milky Way. This puts its brightest stars at magnitude 14 instead of 12, as with M 10 and M 12. With an estimated 1.2 million solar masses, M 14 exceeds its neighbors by a considerable factor.

The distance of M 14 is still debated. Until recently, it was given as about 25,000 light-years, much like its two brighter neighbors. But the Recio-Blanco catalog (2005) now puts it at over 55,000 lightyears.