A system for classifying planetary nebulae
according to their visual appearance. It recognizes the following main types:
More complex structures are characterized by combinations such as "4+2"
(ring and disk), or "4+4" (two rings). The scheme was devised by the Russian
astrophysicist Boris Vorontsov-Velyaminov (1904-1994).
- Stellar image (I).
- Smooth disk (II) (a, brighter toward center; b, uniform
brightness; c, traces of a ring structure).
- Irregular disk (III) (a, very irregular brightness distribution;
b, traces of ring structure).
- Ring structure (IV).
- Irregular form, similar to a diffuse nebula (V).
- Anomalous form (VI).
AND STAR CLUSTERS