NGC 6638 (also ESO 522-SC30 and GCL 95) is a magnitude +9.2 globular star cluster located 30,600 light-years away in the constellation Sagittarius.
The cluster was discovered by German-British astronomer William Herschel using a 47.5 cm (18.7 inch) f/13 speculum reflector at Datchet, Berkshire, on the 12th July 1784.
Right Ascension 18h 30m 56.2s, Declination -25° 29' 45"
