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Planetary Nebulae


The first planetary nebula ever seen by a human was the Dumbbell Nebula, M27 in Vulpecula, which was discovered on July 12, 1764 by Charles Messier when searching for comets and compiling a list of nebulous objects to be avoided by comet hunters. It was subsequently followed by Darquier's discovery of the Ring Nebula, M57 in Lyra in January 1779, shortly before Messier found this same object when tracing the same comet. Darquier was the first to compare the appearance of these objects with that of a fading planet. Following were the discoveries of M76 in Perseus, the Little Dumbbell Nebula, in September 1780 and the Owl Nebula, M97 in Ursa Major in February 1781 by Pierre Méchain.

These four planetaries were all which were known before William Herschel started his comprehensive scanning of the deep sky with large telescopes. One of his first findings within this survey was that of another famous planetary nebula, the Saturn Nebula NGC 7009 (his H IV.1) in Aquarius, in September 1782.

Within subsequent years, Herschel classidied 79 of his deep sky objects as planetary nebulae, of which 20 have been found to really belong to this class of objects. Besides the Saturn Nebula mentioned above, these are:

  • NGC 6369 (H IV.11) in Ophiuchus (Little Ghost),
  • NGC 6894 (H IV.13) in Cygnus,
  • NGC 6772 (H IV.14) in Aquila,
  • NGC 6905 (H IV.16) in Delphinus (Blue Flash N),
  • NGC 7662 (H IV.18) in Andromeda (Blue Snowball),
  • NGC 1535 (H IV.26) in Eridanus,
  • NGC 3242 (H IV.27) in Hydra (Ghost of Jupiter),
  • NGC 2022 (H IV.34) in Orion,
  • NGC 2610 (H IV.35) in Hydra,
  • NGC 6543 (H IV.37) in Draco (Cat Eye N),
  • NGC 2438 (H IV.39) in Puppis (overlaying M46),
  • NGC 2392 (H IV.45) in Gemini (Eskimo N),
  • NGC 6818 (H IV.51) in Sagittarius (Little Gem),
  • NGC 1501 (H IV.53) in Camelopardalis,
  • NGC 40 (H IV.58) in Cepheus,
  • NGC 2440 (H IV.64) in Puppis,
  • NGC 2346 (H IV.65) in Monoceros,
  • NGC 1514 (H IV.69) in Taurus,
  • NGC 6826 (H IV.73) in Cygnus.
  • Moreover, he found 14 planetaries which he misclassified in other categories:
  • NGC 246 (H V.25) in Cetus,
  • NGC 1985 (H III.865) in Auriga,
  • NGC 2371-2 (H II.316-7) in Gemini,
  • NGC 4361 (H I.65) in Corvus,
  • NGC 6058 (H III.637) in Hercules,
  • NGC 6445 (H II.586) in Sagittarius,
  • NGC 6629 (H II.204) in Sagittarius,
  • NGC 6742 (H III.742) in Draco,
  • NGC 6781 (H III.743) in Aquila,
  • NGC 6804 (H VI.38) in Aquila,
  • NGC 6857 (H III.144) in Cygnus,
  • NGC 7008 (H I.192) in Cygnus,
  • NGC 7139 (H III.696) in Cepheus,
  • NGC 7354 (H II.705) in Cepheus.
  • Also, he denoted one part of M76 with an own designation, H I.193, which later found its way in Dreyer's NGC as NGC 651 (so M76 has the two NGC numbers 650 and 651).

    The reason for Herschel's misclassifications is that he had only the appearance of the objects as a criterion, i.e. sorted them according to what they looked like, and little knowledge on their nature.


    Origin: late stage of stellar evolution of medium-weight stars like our Sun.

    PN Mimics

    A considerable number of objects of other nature are not easily distinguishable from planetary nebulae, and has been misclassified because of this. Of William Herschel's 79 objects classified by him as of class IV, planetary nebulae, only 20 are now still considered as such objects, most others being galaxies misclassified as planetaries due to a similar appearance. On the other hand, Herschel classified some planetaries in other of his classes.

    With the invention of spectroscopy, most of these errors could be corrected and avoided in forthcoming work, but a considerable number of misclassifications still occurred. So, Dreyer's NGC in its 67 objects classified as planetaries, contains still 10 errors. At a 1983 IAU symposium, Lubos Kohoutek gave 14 different classes of objects which were mistaken for planetaries more recently (adopted here from Hynes): Emission line galaxies, Supernova remnants, Reflection Nebulae, Classical H II regions, Compact H II regions, Nebulae associated with Wolf-Rayet stars, Symbiotic stars, Slow novae, Be and related stars, Late-type stars with emission lines, Pre-main sequence emission objects, T Tauri stars, Herbig Ae and Be stars, and Herbig-Haro objects. According to Agnes Acker (Astron. Astrophys. Supp. Ser. 71, 163, 1987) who found 206 such errors, the most abundant error sources are symbiotic stars, followed by reflection nebulae, H II regions, and galaxies.


  • Hynes, Steven J., Planetary Nebulae, A Practical Guide and Handbook for Amateur Astronomers. Willmann-Bell, Inc., 1991. Includes 253 finder charts and a catalog of 1340 objects.


    Hartmut Frommert [contact]