Browsing the Hubble Legacy Archive, I was intrigued by a small ring shaped nebula NGC 6369. It is also known as the Little Ghost. Discovered by 18th century astronomer Sir William Herschel, it lies over 2000 lt-yrs away in the constellation Ophiucus. The sun-like star at the center explosively blasted away its outer layers creating the ring of glowing gases. The star radiates strongly in ultraviolet causing the glow of the nebula. The blast also reduced the star to a white dwarf. For this color image, I combined three blue, green, and red filtered grey-scale Hubble images. The colors illustrate the presence of ionized oxygen, hydrogen, and nitrogen atoms.
Fellow amateur astronomer Roger captured an image of his own recently of a different ring-shaped nebula NGC 7293 in his southern hemisphere sky. It is published here in his blog Cosmic Focus.
Astronomy fans are likely familiar with Messier 57 high in the summer sky of the northern hemisphere. It is another fine example of a ring nebula. Follow the link for a beautiful image and description.