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“Horse Head Nebula”
 The horse-head-shaped dark nebula silhouette against the deep-red glow of the background hydrogen cloud definitely become the iconic deep-sky object. There is hardly any popular astronomy book missing its image and Horse Head Nebula many times occurred on front pages of all popular astronomy magazines.

It is very difficult to see the Horse Head by eye even when looking through a powerful telescope Ė rather large telescope under pretty dark sky is needed and the help of visual Hβ filter to enhance contrast is also necessary. This is because humanís eye is quite insensitive to the dark-red wavelength of the Hα line, on which the background cloud mainly shines (the eye sensitivity to the bluish Hβ color is much better and this is why humans see Horse Head better in Hβ, despite the background nebula shines with approximately six-times less intensity in Hβ compared to Hα line). This is why the nebula was discovered in 1888 by Scottish astronomer Williamina Fleming on photographs taken at the Harvard College Observatory.

Low nebula brightness and low sensitivity of humanís eye are no obstacles for highly sensitive CCD cameras, capable to accumulate light for many hours, so the Horse Head was imaged countless times by virtually every astro-photographer. But only a few of them achieve quality rivaling images from large observatory telescopes and the CielBoreal ( and CielAustral ( group of astro-photographers definitely belongs among them. Their incredibly detailed and exceptionally deep image of the Horse Head, acquired with G4-16000 camera on 50cm CDK telescope at their observatory in Chile, shows the Horse Head not as a silhouette only, but also the cloud structure is perfectly visible. Exactly 100 hours of total exposure time in red, green and blue filters as well as narrow-band SII, Hα and OIII filters were necessary to create this fantastic image.

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