Planetary ring nebula in the Lyra constellation (May 20, 2003)

The white arrow points to the position of the central star of this planetary nebula, whose former shell is now visible as a ring of ionised hydrogen (green) and oxygen gas (red). Yet a "white dwarf", the star is so extremely hot that its radiation can only be detected within the ultraviolet range of the light spectrum. Therefore, the star does not seem very bright, eventhough it emits a high amount of radiation.