Propeller Nebula (Simeis 57) in HSTrgb by Jose Carballada Via Flickr: www.astrobin.com/368569 The peculiar nebula Simeis 57. Simeis 57 (also known as HS 191 and C 191) is a high surface-brightness nebula in the constellation Cygnus. The distance nor the source of excitation of Simeis 57 are known.