Spiral galaxy NGC 247 in Cetus (The Whale) is one of several galaxies gravitationally bound to the well-known and nearby Sculptor Galaxy (NGC 253). Whilst large in apparent size at 20 arc min, it has relatively low surface brightness (magnitude 9.9) and needs a fair bit of integration to bring out the details.

Almost of as much interest in the frame is the Burbidge's Chain of 5 galaxies which were "discovered" in 1963. They are designated PGC2796, PGC2794, PGC2798, PGC2791 and PGC842319 (being the dimmest and furthest in angular separation from NGC 247). The chain of galaxies (300 Mly distant) has no physical interaction with NGC 247 (11 Mly distant) but makes an interesting backdrop. Galaxies PGC2798 and PGC2791 are known to have bridging material and this can be seen in integrated subs but remains a future project to get more data to reveal this clearly.

The data was collected over about 15 sessions and 6 weeks and rather late in the season for this object. The observations were hampered by high clouds (not to mention, dodging the Moon and neighbor's sprinkler) on most nights and many frames (including whole nights) were discarded — hence the wacky mismatch in the number of exposures in the different channels. The result is way better then I expected and I'm really looking forward to going deeper later this year. I might even properly focus some subs next time.

Additional Capture Info

The Celestron RASA 8" Astrograph (focal length of 400mm) can actually operate at the seeing limited resolution when coupled with the tiny 2.4 μm pixel ZWO ASI183MM Pro — at a sweet spot of 1.245 arcsec/pixel (which is the same resolution you'd get at a focal length of 633mm with an ASI1600MM Pro). So it is adequate on smaller DSO objects such as galaxies theoretically without compromise (but oversampling with a longer focal length like 1000mm would be better).

During capture every frame high dithering was used and during processing 2x drizzle was employed. For publishing here the drizzled images (0.623 arcsec/pixel) were resampled back to the original native 1x1 resolution (1.245 arcsec/pixel). Dithering probably isn't strictly justified but in processing it seemed to help.

Finally, due to the fast F ratio, the wavelength shift for the geometry of the RASA 8" theoretically averages Δλ = -4.7 nm across the clear aperture (assuming the substrate refractive index is 1.5); so the shifted baseband of the Astronomik Ha 1.25" 12 nm narrowband filter still easily passes the Ha emissions.