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 image 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: The Medusa Nebula (or Abell 21) in Gemini is one of the largest planetary nebulae and yet is very difficult to observe due to a very low surface brightness. Measuring 12.67 by 10.25 arc-minutes in size, the nebula has a surface brightness of magnitude 11.3 and which is concentrated on one side. The nebula lies at a distance of approximately 1000 light-years away with the 16th magnitude bluish star in the middle of the image below being responsible for this stunning and colourful display. Abell 21 is best observed during winter when it lies overhead and a few degrees north of Procyon (mag 0.40).
Please click on either image below to display in higher resolution (1200 x 900)
RA / Dec:
07h 28' 59.5" /
+13° 15' 38"
760" x 615"
Nov 13-14, 2009
02:00 - 05:25 UT+2 (Ç-á)
02:15 - 05:20 UT+2 (RGB)
AP 160 f/7.5 StarFire EDF
AP 1200GTO GEM
Baader 7nm Ç-á
SBIG LRGB + IR-block
1.17" per pixel