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| | Diffuse Nebulae |
 | | Diffuse nebulae, sometimes inacurately referred to as gaseous nebulae, are clouds of interstellar matter, namely thin but widespread agglomerations of gas and dust. |
 | | Diffuse emission nebulae are often called H II regions because they are mainly consisted of ionized hydrogene, H II - the roman number after the element symbol (here H) designating the ionization level: `I' would stand for neutral atoms, the `II' here means first ionization, i.e. |
 | | Diffuse nebulae were longly be considered as distant, unresolved star clusters or star clouds, until in the 1860s spectroscopy revealed their gaseous nature by showing line spectra, in particular due to the pioneering research of William Huggins. |
| www.seds.org /messier/diffuse.html (547 words) |
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