 Some of the knots do exhibit well-developed tails which are often detectable in optical thickness from the visual spectrum.The central PNN was discovered by Hungarian astronomer Jenő Gothard on September 1, 1886, from images taken at his observatory in Herény, near Szombathely.Within the last two thousand years, the central star of the Ring Nebula has left the asymptotic giant branch after exhausting its supply of hydrogen fuel.