1	0	Stars
2	1	Nebulae
3	2	Bipolar Nebulae
4	2	Bright Nebulae
5	2	Compact Nebulae
6	2	Dark Nebulae
7	6	Bok Globules
8	2	Dense Clouds
9	2	Dense Matter
10	9	Diffuse Nebulae
11	9	Dust Nebulae
12	2	Emission Nebulae
13	12	H II Regions
14	13	Compact H II Regions
15	12	Herbig Haro Objects
16	12	Planetary Nebulae
17	2	Filamentary Nebulae
18	2	Gaseous Nebulae
19	18	Emission Nebulae
20	19	H II Regions
21	20	Compact H II Regions
22	19	Herbig Haro Objects
23	19	Planetary Nebulae
24	2	Planetary Nebulae
25	2	Reflection Nebulae
26	2	Ring Nebulae