I. Galactic nebulae: Symbol Example
A. Planetaries P N.G.C. 7662
B. Diffuse D
1. Predominantly luminous DL N.G.C. 6618
2. Predominantly obscure DO Barnard 92
3. Conspicuously mixed DLO N.G.C. 7023
II. Extra-galactic nebulae:
A. Regular:
/ N.G.C. 3379 E0
1. Elliptical En / 221 E2
(n = 1, 2, ..., 7 indicates the \ 4621 E5
ellipticity of the image \ 2117 E7
without the decimal point)
2. Spirals:
a) Normal spirals S
(1) Early Sa N.G.C. 4594
(2) Intermediate Sb 2841
(3) Late Sc 5457
b) Barred spirals SB
(1) Early SBa N.G.C. 2859
(2) Intermediate SBb 3351
(3) Late SBc 7479
B. Irregular Irr N.G.C. 4449
Extra-galactic nebulae too faint to be classified are designated
by the symbol “Q.”