Details: . M57 was discovered by Charles Messier in January of 1779. While searching for comets, objects like M57 often confused Messier’s efforts since they might resemble a comet, therefore he made a catalog of permanent, non-moving objects like M57 so as to not confuse them with comets. Visually M57 is a bit larger than Jupiter, resembling a fading planet, and may have contributed to the term "planetary nebula" for these types of objects. Messier incorrectly assumed this nebula was a group of tightly integrated stars, so far away but so close to each other, that they were unresolvable through his telescope.
A couple decades later, German astronomer, Count Friedrich von Hahn, discovered the central star, clearly visible in the image above, but then noted that he later could no longer see it, presumably due to changes in the ring nebula. Later as astronomers began to more closely study planetary nebulae, they discovered that their spectra emitted bright emission lines similar to florescent gasses and concluded that these were glowing clouds of gas, not groupings of distant stars!
M57 one of the nearest planetary nebulae at about 2500 light years from Earth, meaning the light we see today left the nebula about 500 years B.C.!  Images of M57 taken over more than 5 decades show it is expanding slowly at 1 arc second (1/3600th of a degree) every 100 years or about 30 km/s. It is estimated to have been expanding for 1600 years, thereby it started expanding roughly 4100 years ago (i.e. 2500+1600 years). The diameter of M57 is between 1 and 2 light years, that is, over 1000 times the distance to Pluto. The light of M57 reaches us as both reflected and emitted light. The central star is a white dwarf that illuminates the shell of material, but it also exciting the ionized gasses causing them to emit different light frequencies. The blue light is from doubly ionized oxygen and the red light from ionized nitrogen.
The structure of the nebula appears spheriod, that is a stretch sphere resembling a football. It was initially thought that as we looked through the spheroid, the ring shape was caused by seeing through more material at the edges than at the center, making the edges look more dense. Modern studies, however, have indicated that it is more likely to be cylindrical and shape like that of a lidless tin can, with the top of the can facing us. Therefore, we are looking almost through the top of the lidless can with its walls forming the ring.

Annotations. In the image above, hover a mouse or curser over the image to show annotations of M57, with several enlarged insets identifying interesting features! The central star can be clearly seen in the middle of the blueish center. Note also there are three visible shells of material – the inner ring itself, a first reddish shell outside the ring and a 2nd very faint reddish shell outside the first. Also note four different galaxies highlighted beginning with PGC 62532 at the left side. While this galaxy appears visually smaller than M57, it is likely 100,000 times bigger because it is so much further away and outside our own Milky Way galaxy. Also note even more distant galaxies as annotated next to the insets. Two galaxies are even visible through the outer shells of M57.

Below Images: In the first image below, the same image has been processed to remove all foreground stars as these stars are all within our own galaxy. This is what the view would appear like if no stars existed along our line of sight. Using a mouse to hover over the image, brings all the stars back. Of course the central star is still visible, it has not been removed! The second image below shows an enlarged and cropped version of M57 and this time hovering a mouse makes the stars disappear. Finally, the third image below is the same image, same data with my previous pre- and post- processing workflow. Hovering over the third below image shows a direct comparison to the current processing workflow using PixInsight software for the majority of stacking and sharpening, with Photoshop used for final touch-up. Note the improved color throughout the image from object to stars, as well as a visually and more natural look of very faint stars and very enhanced object details.

Object Statistics: Constellation: Lyra, Right Ascension: 18h 53m 53s, Declination: +33° 01' 48”, Magnitude: 8.8, Size: 10.3'x8.1', Distance 2500 ly, Size 1-2 ly.