Hello everyone.
I think I might go back and add a few more hours luminance and some Ha to this galaxy but for now I have accumulated 20.5 hours on this LRGB image of NGC 1808.
Taken with the 12.5" RCOS and SBIG STL11K at Yass.
I just love the galaxy pair you can see at the 5 o'clock position on the edge of the image.
I must say that I am really pleased to find that you have done a really high quality image of this galaxy, as previous amateur images of this galaxy have been of modest quality.
This is actually one of the most unusual members of the population of bright galaxies.
If one assumes that the outer portions of this galaxy are essentially circular (in real three-dimensional space), then one is forced to conclude that the bright body of this galaxy is not intrinsically round;
this is therefore an example of a galaxy with an intrinsically oval inner disk (yes, not all spiral galaxies are round!)
(another example of an oval galaxy is NGC 1566)
In my view (and I have pondered the morphology of this galaxy over many years....), the inner oval disk of this galaxy actually forms a bar within the faint outer spiral arms, and there is another bar within the bright inner oval disk!
The well-behaved radial dust "spokes" coming from the central starburst region are very rare (or absent) in the other members of the population of bright galaxies.
I have searched tens of thousands of galaxy images for this sort of feature...... and it is either very rare, or absent.
I believe (from memory) that Dr William Keel (an expert in active galactic nuclei) did a similar search for low entropy radial features in the central parts of galaxies, and that he came to the same conclusion.
cheers,
Robert
P.S. the central starbust region in galaxies usually has high extinction in front of it, but this is emphatically not the case in this galaxy.
"Just for fun and profit", I attach here - for comparison purposes - the Far Ultraviolet + Near Ultraviolet image of NGC 1808, taken with the GALEX satellite.
FUV is displayed as blue and NUV is displayed as yellow.
In general, FUV is an excellent tracer of the distribution of massive hot OB stars ( and thus, it is a tracer of current star formation), but with the qualification that FUV light is highly subject to severe extinction from dust within a galaxy.
Last edited by madbadgalaxyman; 16-12-2012 at 11:35 PM.
Reason: more
Stunning work yet again Martin, this galaxy has a very interesting structure and you have really captured it well. Beautiful colours too and all those background galaxies look fascinating, there are so many shapes and sizes. Thanks for the view.
Had some good seeing during this data capture also and I started collecting some additional lum and Ha last night. The seeing was particularly good last night, as evidenced by the exquisite guiding that was going on through the night. Check out the thumbnail attached.
Thanks all, especially for the detail there Robert.
cheers
Martin
Hello Martin,
I actually got Professor Kenneth Freeman (the recent winner of the Prime Minister's Prize for science) interested in this galaxy by referring him to your image of N1808.
[[ Freeman is a leading authority on just about every aspect of extragalactic astronomy; in fact, the totality of Professor Kenneth C. Freeman's work would probably earn him a Nobel, if nobels were awarded for the total of a lifetime's work (which they aren't).
Ken Freeman has made fundamental contributions to stellar astronomy, Milky Way structure, galaxy evolution, the modelling of the 3D shapes of elliptical galaxies, kinematics & morphology of spirals and ellipticals, dark matter distributions, the study of disk galaxies, etc. etc.
He is in every way comparable to the other great extragalactic astronomers of the last 100 years. ]]
[[ like John von Neumann, Freeman has had less recognition than he should have had due to the great diversity of his work]]
It is uncommonly hard to get Professor Freeman fired up about something, because he knows much much more than the average extragalactic astronomer!!(hard to say something new to him, as he is the Renaissance Man of extragalactic astronomy)
cheers, Robert
Last edited by madbadgalaxyman; 18-12-2012 at 12:24 PM.
Reason: typos, and more info
Next month I'll take a look. 
