NGC 2404 NE of the core is the most prominent HII region. It is round and much better defined visually than even the core of the galaxy. This was the only feature noticeable at 125x in the 12” SCT. Coincidentally NGC 2404 was discovered by Bigourdan with a 12" refractor.
With time, at 225x, the threshold companion of the star to the S of the core becomes visible along with the large nebulosity that seems to surround the pair. I spent some time watching the shifting appearance of this region, and concluded that both the nebulosity and the threshold companion were real. Subsequent inspection of CCD images confirmed the companion and the general enhancement in that area, which involves the prominent star association 41 (Hodge, PASP 1985), the weaker association 35, and a semicircle of small HII regions. It is not clear from the comparison with the photos why the nebulosity as seen visually seemed to concentrate around the fainter star, but this of course is not impossible. The region deserves a closer inspection.
The NW “branch” suddenly popped into view later. It is interesting how inconspicuous this feature was, considering that it was described by Herschel. The other apparent arm fragment along the SE edge of the halo was even more ephemeral at 225x.
NGC 2403 is Herschel's V.44 (a "very large nebula") and belongs to the M81 group. It is a Herschel 400 object and as such I observed it previously with my 4", the Comet Halley Renaissance. It is also on the Caldwell list as #7.
NGC 2403 is Herschel's V.44 (a "very large nebula") and belongs to the M81 group. It is a Herschel 400 object and as such I observed it previously with my 4", the Comet Halley Renaissance. It is also on the Caldwell list as #7.
