Witch Headache

The Witch Head Nebula above is a target I’ve wanted to capture for a long time now.  It is a very large, and very diffuse reflection nebula, and therefore very dim, and must be captured with broadband (RGB) filters – from a dark sky site.  In the Winter.  Back home in the Pacific Northwest I never venture out to dark sky sites in the Winter because it’s too risky.  That is, even if you don’t get caught in a storm or stuck in a snow drift, there’s a good possibility that the weather will change and the whole trip will be a waste of time.  So I was excited about the possibility of capturing the Witch Head from the observatory in Australia.

The location of the observatory is not exceptionally dark, but better than any place that I could get to easily.  The problem was that this nebula is too large to fit in the field of view of the telescope/camera combination there.  The above image is a mosaic of 2 panels, and it barely fits in that.  But it turned out that doing it as a mosaic created its own problems.  There was some background gradient (gradual change in brightness) in both frames, and they didn’t match.  This problem was exacerbated by the need to use a lot of stretching to reveal the faint nebulosity.  The result is that it took hours of additional work to put the two images together, and it is still quite obvious that the upper and lower halves don’t match.

Of course, I could attempt to capture this target during my vacation here in southern California using my wide-field system to get it in a single shot.  Ideally, this would mean making some long trips to the darkest places around here and collecting many hours of exposure, which doesn’t seem very realistic.  Or fun.  So maybe I’ll just see what I can get close by.  And maybe it would make more sense to start over again with the raw data from Australia and see if I can’t get a better match between the upper and lower halves.


About Greg Marshall

I am a retired electronics engineer and after a few months of enjoying my leisure I began to miss doing product development. My astronomy hobby always needed new solutions to unique problems, so I decided that whenever I came up with a good solution I would try to make it available to others.

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