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Published online by Cambridge University Press: 27 June 2016
The emission nebulae, as more or less compact gaseous or gas-and-dust formations, belong to a rather widespread type of population in our Galaxy. Though, for well-known reasons, we are able to penetrate into the depth of the Galaxy no further than 2–3 kpc for H 11 regions, several hundred nebulae have already been recorded (predominantly in the spiral arms). Sometimes the emission nebulae almost entirely occupy large regions of the sky, as, for instance, in the region of ρ, γ and o1 Cygni. In addition, in the area within latitudes ± 5°, we observe a nearly continuous faint emission background.