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 74 in Vulpecula is a very large ancient planetary nebula spanning 15 arc-mins by 13 arc-mins in apparent diameter and which translates to a physical size of 16.0 by 13.7 light-years (Table 3, Tweedy and Kwitter). However, it is quite dim with a mean surface brightness of only 17.6 mag/arc-min2. As indicated by the image below, the envelope is quite smooth and generally even in brightness with no indication of an outer shell. Abell 74 has been confirmed by Tweedy and Kwitter to be interacting with the ISM (interstellar medium) and with its mag 17.11 degenerate white dwarf central star, WD 2114+239, to have an effective temperature of 66,000 degrees Kelvin and to lie 1,120 light-years away (see Table 4). An alternate study characterizes WD 2114+239 with an effective temperature of 108,000 degrees Kelvin and to lie at a distance of 2,450 light-years away (see Table 1). As suggested by the image below, the overwhelming proportion of the signal is in the h-alpha emission line with additional signal available in NII (Plate 51, Tweedy and Kwitter) and much weaker signal in OIII restricted to the central portion of Abell 74.
Please click on the image below to display in higher resolution (1200 x 900)
RA / Dec:
21h 16' 52" /
+24° 08' 51"
871" x 791"
Aug 22-23, 2011
21:45 - 04:05 UT+3
AP 305/f3.8 Riccardi-Honders
AP 1200GTO GEM
Baader H-a 7nm
SBIG LRGB filters
1.25" per pixel