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NGC 6888, The Crescent Nebula in Cygnus

Background information and spectra

aka: Sharpless 105, Caldwell 27

The Crescent nebula, discovered in 1792 by William Hrschel, is an emission nebula. It arises from the stellar wind from the
Wolf-Rayet star WR 136. This star has a surface temperature of over 70,000 K and is emitting a strong stellar wind.

The energetic wind is interacting with material blown off the star when it was in the red giant phase about 300,000 years ago.
This interaction, together with the intense radiation from the star, is causing the gases to fluoresce.

Image of NGC6888 is here

Spectra of various regions of NGC 6888


Region 1 - Bright red reqion in north


Spectrum shows weak oxygen, strong nitrogen and traces of heliom and sulphur.
Blue region weak, probably due to dust.

Region 2 - Bright bluer region


Stronger oxygen, weaker nitrogen.
Less dust?

Region 3 - Fainter knot in lower area


Stronger nitrogen and sulphur.

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