George Abell's examination of the Palomar Observatory Sky Survey in the mid 1960's yielded 86 planetary nebulae which have proven to be an observer's dream challenge, for many of these celestial objects are not only very faint in magnitude even under very dark skies but are also relatively large with dimensions often measured in minutes in lieu of seconds. Later analysis of Abell's catalog revealed that at least four of these objects, namely Abell 11, 32, 76 and 85, are not planetary nebulae at all. For the avid observer, an O-III filter is highly recommended in order to have any hope of visually detecting these elusive wonders.

An even greater number of planetary nebula can be found within the NGC and IC catalogs and are available elsewhere on this site (see here). As is evident from the images below, planetary nebulae are beautiful to look at thanks to the glowing and colourful gaseous shrouds which make their planetary appearance and colouration possible as a result of stars having exhausted their nuclear material and having reached the last stages of their life. Some of the more exotic planetary nebulae include the Cat's Eye (NGC 6543), the Saturn Nebula (NGC 7009), the Ghost of Jupiter (NGC 3242) and the Owl Nebula (M97).

Note: Abell 61 in Cygnus is a relatively large ancient planetary nebula spanning 200" in apparent diameter. However, it is quite dim with a mean surface brightness of only 15.4 mag/arc-min². Similarly, the central star responsible for the impressive circular and smooth nebulosity is also very dim (mag 17.39) and is binary in nature. According to Chu et al, a white dwarf star is involved (WD 1917+461) and whose effective temperature is 88,000 degrees Kelvin. Abell 61 is expanding at about 30 km/sec and its kinematics suggest a stellar explosion about 22,000 years ago (see Tweedy and Kwitter). Abell 61 lies approximately 4600 light-years away and has been confirmed to be interacting with the ISM (interstellar medium). As indicated by the image below, the inner envelope is quite smooth and even in brightness with no indication of an outer shell.