Supergiant star in Cygnus Heart

Nights in July are short, and long time deep sky exposures must be split into several days to achieve decent result with many-hours images. However with fast lens it is possible to fairly quickly collect some decent result. The picture above presents centre of Cygnus constellation. Large star in the left image part is Sadr – Gamma Cygni. There are plethora of deep sky objects in this frame – you can see famous Crescent NGC6888 nebula in the bottom part, few dark Barnard objects, well known Butterfly Nebula that surrounds Gamma Cygni, whole lot of open clusters and red hydrogen clouds. There is annotated image below.

HaRGB composite of Cygnus constellation centre.

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Annotated image

Among many stars in this area I annotated one – KY Cygni (next to M29 cluster in the lower left part). This is red supergiant star, one of the largest known stars. According to different estimations its size between 6.6 and 13.3 astronomical units. So if we place this giant in the Solar System centre it would extend beyond the Jupiter orbit, or maybe even Saturn orbit. It is also very luminous star with luminosity of 300 000 or more times the Sun’s luminosity. However in the picture it is pretty faint – there are two reasons for it. First – it is very far, about 5000 light years away. Secondly, and more important, its light is absorbed by large amount of interstellar matter. Due to this extinction KY Cygni is 7.75 mag fainter (so over 1000 times fainter) than if not light was lost.

These image were made at my backyard in July, 2017 with Samyang 135/2 lens on Smart EQ mount. RGB is 40×3 minutes with QHY163C camera, hydrogen alpha is 24×5 minutes with QHY163M camera. Lens was stopped down to f/2.8.

Gamma Cygni region in hydrogen alpha band.

Large version

Clear skies!  

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