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Left hand down a bit


AusGuy
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Old enough to recognise the heading to this post? Leslie Philips' catch phrase in The Navy Lark a radio program which ran from 1959 to 1976.

If you start at the Lagoon Nebula showing in its usual orientation and move about a degree to one side and down a bit you'll come to this very interesting patch of sky. Located in the Sagittarius arm of the Milky Way and floating in front of the myriad background stars there is this mix of dark, emission and reflection nebulae.

Last night the Moon was waxing gibbous being 78% lit. Normally I wouldn't have bothered to view this kind of object in such conditions but I wanted to see what difference a new Baader Neodymium (Moon and Skyglow) filter could make and it sure didn't disappoint. With the camera set to bin-2 mode, gain set to 400 and exposure set to 60 seconds the 8 inch Newt picked up quite a respectable on-screen view. Not a patch on long exposure images of course but satisfying nevertheless. This is one more target to add to the public outreach viewing list when, one day, we can once again get out among the public.

This was the last target viewed for the night and after shutting down I noticed that the main mirror was slightly dewed over, Did that affect the quality of the image? Hard to say. I'll try again and compare in a few weeks time when the object will be higher in the early evening sky at a time that is less prone to dew. What was certain was the the outside of the observatory's dome was quite literally streaming with dew run-off. It's quite remarkable how the dome creates its own favourable mini-climate even 'though it has an extremely wide up-and-over viewing slot.

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The later processed image better displays the emission and reflection nebulae.

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The labelled version identifies some of the many distinct objects in view and gives some background information as to distance and size. The main part of the diffuse nebula is IC 4685 across which you can see dark nebula segments snaking their way. One of them is catalogued as Barnard 303. I couldn't find catalogue numbers for the other parts. NGC 6559 is given to both the bluish reflection nebula surrounding a small group of stars and the bright red shell-like emission nebula close by, probably because the same stars are making both nebulae visible. The separation of the two lobes IC1274 and IC1275 is caused by the superimposition of the dark nebula Barnard 91 which is simply part of the much larger cloud of cold dark gas and dust that runs from top to bottom through the frame. Clearly this is closer to us than most of the background stars unlike the smaller and fainter dark streak further over to the right. That is at least partly covered by the background stars. IC 4684 near the bottom of the frame is another reflection nebula.

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As to distance and size, it was somewhat difficult to find out precisely how far away these objects are. Most internet sources quote either 4,000 ly or 5,000 ly but they were not what I would regard as authoritative typically being postings of amateur images. One outlier was an image taken from Namibia and that quoted 5,800 ly. Given the excellent nature of that image and the painstaking care that must have gone into creating it, it is reasonable to give more credence to the distance value it quotes. So it seemed reasonable to use a distance of 5,000 ly here with this image. On that basis the image spans 121 x 82 ly. The size of IC1274 is 11 ly, the length of the red emission nebula part of NGC 6559 is 13 ly and IC4684 is 4 ly across ( Sol to Alpha Centauri).

Vixen R200SS; SW AZ-EQ6 Pro, ZWO ASI294MC Pro bin-2; Baader MPCC; Baader Neodymium (Moon and Skyglow) filter, Bortle 4.5

SharpCap livestack 17 x 60 seconds exposures at 400 gain. Later adjustment in Photoshop.

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Hi, wonderful shot and as you know I do enjoy the added information - makes it so much more worthwhile and informative. Interesting to note your use of the  Baader filter - I have never thought to try that.

Mike

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  • 3 weeks later...

Mike - based on past experience when using an uncooled Sony IMX178 camera I bought a 2” version of the Baader filter to go with the then new ZWO ASI294MC Pro. But in the hurly-burly of getting to grips with the new camera and new (to me) software SharpCap I never could quite get things to work properly when using the filter and eventually I put it aside. Some 8 months later I thought that I'd try it again and after creating some new flats it immediately worked like a charm. As they say, “go figure”. The consequence has been that for the last few months I have mostly avoided viewing when more than an eighth Moon is up due to the sky glow it creates but now I'm quite comfortable getting out under most Moon conditions. So using the filter allows me to greatly extend my viewing time. And even on moonless nights in my Bortle 4.5 area it does quite a good job of suppressing the effect of the light dome that rises over my neighbouring city. Also, I haven't noticed that it adds the need for much, if any, extra exposure time when viewing. So, although a bit pricey, I do recommend using the filter as a very productive unit.

David

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