"dim astronomical objects" . "star formation" . "Nebula" . "gas-cloud" . "gas cloud" . "nebulous" . "interstellar nebulae" . "interstellar nebula" . . . "Crystal Nebula" . . . . . "reflection nebula" . . . . . "bright nebula" . "Nebula" . "spiral nebulae" . "nebula" . . "N" . "nebulosity" . "Nebulae" . . "extended objects" . . "dust cloud" . . "Nebula#Diffuse nebulae" . "gaseous nebulae" . "nebulous objects" . "clouds of gas" . "Nebul\u00E6" . . . . "diffuse nebulae" . "Nebula#Observational history" . "nebulae" . . "nebul\u00E6" . . .