M14 is a globular cluster located in the southern constellation Ophiuchus. It lies at a distance of 30,300 light-years from Earth at right ascension 17h 37m 36.15s and declination: -03°14’45.3” and has an apparent magnitude of 7.6. It has the designation NGC 6402 in the New General Catalogue and is also known as BD-03 4142, C 1735-032, GCl 72, HD 159974, GCRV 10179, MWSC 2643. Messier 14 is elongated in shape and contains about 150,000 stars. It occupies an area about 100 light-years across in size. The brightest star in the cluster has a visual magnitude of 14 and the average apparent magnitude of the cluster’s 25 brightest stars is 15.44. The cluster has only about 5 per cent of the Sun’s heavy elements. Its estimated age is about 13 billion years. Messier 14 is a class VIII globular cluster, which means that its stars are not particularly densely concentrated in the central region. The cluster’s bright main portion spans only 3 arc minutes in angular diameter, but the outermost regions give M14 a total angular diameter of 11.7 arc minutes. Astronomers have discovered about 70 variable stars in M14. Many of these are classified as W Virginis variables, a subclass of Type II Cepheids commonly found in globular clusters. M14 also contains a considerable number of RR Lyrae variable stars, which are used to calibrate distances to objects within the Milky Way. A nova occurred in M14 in 1938 and reached a visual magnitude of +9.2, but was not discovered until 1964, when astronomers surveyed a series of photographic plates from that period. The photographs were taken by the American astronomer Helen Sawyer Hogg between 1932 and 1963 with a 72-inch reflector at the Dominion Astrophysical Observatory in British Columbia. This was the first nova ever photographed and the second to be discovered in a globular cluster after the 1860 nova observed in Messier 80. A carbon star was discovered in the M14 cluster in 1997. CH stars are a very specific type of Population II carbon stars that can be identified by CH absorption bands in the spectra. Middle-aged and metal-poor, these under-luminous suns are known to be binaries. The star’s carbon-enriched core likely reached up to the surface after the star had lost its outer layers in close encounters with other stars in the cluster. Messier 14 has an absolute magnitude of -9.12 and a total luminosity about 400,000 times that of the Sun. While it appears fainter than Messier 10 and Messier 12, the other two famous globular clusters in Ophiuchus, M14 is the largest of the three and has a significantly greater intrinsic luminosity than the other two. It is almost twice as distant as M12 and more than twice as distant as M10.
The cluster was discovered by Charles Messier, who described it as a nebula without stars and catalogued it on June 1, 1764. William Herschel observed the cluster in 1783 and was the first to resolve it into individual stars.
Messier 14 is located 0.8 degrees north and 10 degrees east of Messier 10 and about 21 degrees east and 0.4 degrees north of the star Delta Ophiuchi. It can be found about one-third of the way from Beta to Eta Ophiuchi. The cluster can also be located along the imaginary line from Cebalrai, an orange giant with an apparent magnitude of 2.76 and the fifth brightest star in Ophiuchus, to Antares, the bright red supergiant located in Scorpius. The much fainter globular cluster NGC 6366 can be found just over 3 degrees to the southwest of M14. The best time of year to observe the cluster is in the months of May, June and July. Credits: Messier Objects, NASA, Universe Today, Wikipedia.