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Originally Posted by madbadgalaxyman
An interesting experiment, Steven! The neb may look the same as at longer wavelengths, but the dust lanes are enhanced!
As you know, a Johnson-Cousins (or similar) U -band filter is potentially useful for emphasizing OB stars..... but the extinction is high in this regime, so the reduction of starlight by interstellar dust can greatly negate the impact of the better isolation of hot young stars when using this filter.
Short wavelength filters greatly emphasize the dust distribution within an object or in a galaxy image, and this seems to be the case in your M42 image, which shows the dust distribution in the nebula extremely obviously. Perhaps deep Ultraviolet imaging of this region can show the cold & dark and dusty Orion Molecular Cloud from which stars are forming, as seen against a stellar or nebular background?
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You are correct the dust lanes are much more pronounced, more so in M43 than M42. I think I suffered from "mind blindness" by concentrating on differences in the highlight areas and failing to note changes in the shadow or dust areas.
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Here is a "fun" collection of images of M51, using several individual filters of progressively longer wavelengths, in order to illustrate the effect of isolating progressively longer wavelengths with specific filters. In order, the images are taken with the following filters:
B -band ("blue")
V -band (approximately "visual")
I band (very near infrared, around 800nm)
Near-Infrared (image is a composite of J+H+K bands)(all filters in this composite are >= 1.0 microns)
Given that each colour filter gives a unique image, I will repeat a comment I made in a previous post.... that we actually lose information by adding the images together that are taken with various filters. Your experiments with imaging in various filters are a good illustration of the usefulness of not "adding everything together"!
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Note added in later Edit
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A most interesting comparison.
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NGC 253 is noted for being particularly red in its optical colours, compared to the color that would be expected for its optical-wavelengths derived Hubble type; because the the dust screen is so heavy within NGC 253, it does not surprise me that very little ultraviolet light got through to your CCD!!
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The moral of the story here is that UV imaging requires far more preparatory work than simply finding the RA and Dec of the object you want to image.
The dust lane detail in NGC 5128 is making it a far more interesting proposition to image in UV.
Clear skies
Steven