NGC 6939 (also Collinder 423, Melotte 231 and OCL 217) is a magnitude +7.8 open star cluster located in the constellation Cepheus.
The open cluster was discovered by German-British astronomer William Herschel using a 47.5 cm (18.7 inch) f/13 speculum reflector at Observatory House, Windsor Road, Slough, Berkshire on the 9th September 1798.
Right Ascension 20h 31m 30.0s, Declination +60° 39' 42"
