There are many ring-shaped planetary nebulae in the sky but only one Ring Nebula. One of the most striking objects to see visually by telescope, the Ring Nebula is unusually bright. In fact, it is one of the few planetary nebulae that I have to image narrowband at 1 minute subs (instead of 5 minute) with this camera to avoid oversaturating.
The planetary nebula is located 2300 light years away in the northern constellation of Lyra. The bright region of the nebula is 1.5 arc-minutes in apparent length, which corresponds to a true span of about 1 light year.
Similar to the much larger Helix Nebula (NGC 7293), this nebula is a bi-polar nebula and our view is aligned at about 30 degrees from the bi-polar axis. Around the center of the nebula, a torus of dense dust creates the bright white region by constraining the bi-polar outflow into a dense ring, which we see at a slight angle that presents an apparent oval shape instead of a circle. In addition to constraining and concentrating the gas, the torus directs the outflow into two large opposing end-on lobes, which are the faint outer regions that we see in the image.
To help visualize the description above, in Revision C I have attached a schematic from the paper,
Studies of NGC 6720 with Calibrated HST WFC3 Emission-Line Filter Images–I: Structure and Evolution. Revision D shows an approximate view of what M57 might look like from an exact end-on view.
The galaxy at upper right is IC 1296, a face-on barred spiral galaxy. This galaxy is far in the background, at 220 million light years away, and has a true diameter of about 40,000 light years.
Although this is one of my favorite objects for the eyepiece, it is one of my least favorite to image. It is very hard and frustrating to capture and process all of the beautiful aspects of this object into one image - the bright detailed inner region, the faint outer region, and the colorful starfield.
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