At the end of August I collected some more light to extreme classic – NGC6888 Crescent nebula in Cygnus. It is emission nebula placed about 5000 light years away that has been formed from massive stellar winds that comes from Wolf Rayet star WR136. To see it visually you would need proper filter and an instrument with aperture at least 80-90mm under good conditions. But here at the long exposed image we can investigate a bit better its sophisticated structure. Image is a composite made with RGB filters and narrowband hydrogen alpha and oxygen iii filters. Total exposure time was near 20 hours – it is 8.5 hours of Ha, 8.5 hours of Oiii and 3×30 minutes of RGB. I had two main goals in mind – first, to catch nebula oxygen envelope, and second – to register Soap Bubble nebula. This last one is faint, circular shaped gas bubble, that has been discovered only ten years ago. And fortunately even under suburban skies both goals have been achieved, although I left Soap Bubble and oxygen envelope not well defined – I wanted to keep right proportions between relative luminance. They are pretty faint.
Picture was made with my current setup – 130mm refractor, QHY163M camera and EQ6 mount over few August nights. Here is hydrogen channel only, this usually provides the most detailed image:
And last but not least RGB image – this is only 3×30 minutes of exposure, but it gives an idea on how the “natural” colored Crescent would look like: