NGC 6639 (also OCL 57) is a magnitude +9.2 open star cluster located 2283 light-years away in the constellation Scutum.
The cluster was discovered by British astronomer John Herschel using a 47.5 cm (18.7 inch) f/13 speculum reflecting telescope at Windsor Road in Slough, Berkshire on the 31st July 1826.
Right Ascension 18h 30m 57.8s, Declination -13° 10' 14"
