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 39 in Hercules is one of the most recognized entries within the Abell catalog owing to the fact it is perfectly spherical and with a dominant blue central star (both of these characteristics typify the classical planetary nebula). Images of Abell 39 using much greater aperture will reveal at least one galaxy visible "through" the turqoise disk between the two and three o'clock positions and which is also visible in the image below. The brighter perimeter of the spherical bubble is believed to be a second and larger halo encompassing a smaller internal bubble. The central star at magnitude 15.69 is a white dwarf which is believed to have exploded 22,000 years ago based on its kinematics and current rate of expansion (35 km/sec). Abell 39 lies approximately 7,000 light-years away and spans another five to six light-years across and represents one of the largest such spherical nebulae known. With an integrated magnitude of 13.7, Abell 39 is quite dim and requires large aperture instruments and/or extended exposures to be captured. Perhaps the most recognized image of Abell 39 is the one taken using a special blue-green filter by the 3.5-meter telescope at Kitt Peak National Observatory at Tucson, Arizona (click here).