Old photographs show no evidence of the above nebula. In 1992, a white dwarf star toward the constellation of Cygnus blew off its outer layers in a classical nova explosion: an event called Nova Cygni 1992 . Light flooded the local interstellar neighborhood , illuminated this existing gas cloud, excited the existing hydrogen , and hence caused the red emission . The only gas actually expelled by the nova can be seen as a small red ball just above the photograph's center. Eventually, light from the nova shell will fade, and this nebula will again become invisible!
Media Credits & Attribution
Credit: Peter Garnavich ( Notre Dame ), 1.2-m Telescope , Whipple Observatory