For a glance at a planetary nebula we may turn with the five-inch to No. 4234.
Its visual appearance in the great telescope was now also that of a planetary nebula.
A star has actually, under our eyes, become a planetary nebula, and the cycle of which he gave the first terms is complete.
A nebula consisting of a rapidly expanding shell of glowing gas, mostly hydrogen, ejected from a red giant upon its collapse into a white dwarf. Ultraviolet radiation from the hot, luminous white dwarf ionizes the expanding gas and causes it to glow. The nebula disappears once the cooling dwarf can no longer ionize it, and its material eventually returns to the interstellar medium. See more at white dwarf.