I sat in the shade of Mark W.'s car and we chatted as I ate my dinner. Once the sun set I started to set-up: 4-inch refractor paired with a C8 on an alt/az mount. It was the first time using the C8 and I spent around 15 minutes getting the collimation done, and felt it was pretty good but probably not perfect. I also brought my mirror mount. Transparency was hurt by some wildfire smoke which came over just at dusk. SQML read 21.4 at midnight. I observed until 3am before packing in and getting a couple hours sleep until morning.
With Scorpio high in the sky, I spent the about half an hour observing Sivan 8, a large circular structure at the western curve of the bottom of Scorpio's tail. It contains RCW 113 (=Gum 55), which GalaxyMap describes as "a huge region of diffuse nebulosity surrounding the Sco OB1 association and its core ionising cluster, NGC 6231". RCW are Alex Rodgers, Colin Campbell, and John Whiteoak, who, working at Australia's Mount Stromlo observatory under the direction of Dutch-American astronomer Bart Bok, published a catalog of 182 nebula in the southern skies in 1960. They used a Meinel-Pearson 8-inch f/1 flat-field Schmidt with various filters, including Ha. RCW 113 is described in the catalog as a "Large loop of ionization in region of fainter emission." Gum says it is "A large roughly semicircular loop, whose ragged appearance is due in part to overlying obscuration. At its centre is the galactic cluster NGC 6231, which is the nucleus of an O-Association". I used the Sivan and RCW boundary descriptions to indicate the extent of the nebula delineated by their designations.
I have been engrossed with this area since observing the Sivan nebula this last fall and spring. Astrophotos show the giant circular structure but also a couple dark, Elephant Trunk-like cometary nebula, particularly one cataloged as SFO 82 (nicknamed "The Dark Tower of Scorpius"), along with several Horsehead-like dark nebula intrusions into the brighter wispy nebula. Using my 4-inch with PVS-14 and 3nm Ha, SFO 82 was seen faintly as a cone-shaped dark nebula with bright nebular sides; the 3nm Ha filter cut the brightness of the star at its tip quite a lot. The elephant trunk extends approximately 30' to the WNW into the surrounding nebula. The paper I referenced above indicates SFO 82 is part of Sco OB1 and that the trunk is likely being shaped by radiation and gas pressure interactions with NGC 6231. When observing this area with Mark W., I pointed out the two wedge-shaped dark nebula along the southern rim, in line with the star chain formed from IC 4628 through NGC 6231. The 4-inch gives a 5° TFOV, so some panning of the scope is needed to take in all of Sivan 8, which is 7°x7°.
Image from the SuperCMOS explorer via GalaxyMap, with my annotations of the designation diameters according to the dimensions given in the respective discovery papers.
Panning the telescope 9° to the southwest we arrive at the center of RCW 114, a very large, wispy nebulous area. GalaxyMap says "This huge but very faint nebula is probably a ring nebula surrounding the Wolf-Rayet star WR 90, expanding into a pre-existing cavity created by the supernova remnant SNR 343.0-06.0." Distance estimated at 1500pc, so it might not be related to Sivan 8 / RCW 113, which has distance estimates between 1640-2000pc, even though the wisps between the two regions appear to connect them. Called the "Dragon's Heart" nebula by astrophotographers, it appeared as a giant "C" filling a 5°x5° area, with the brightest thin wisps to the east and south, and much fainter nebula filling in the open part of the "C." Here it is in relation to Sivan 8:
I panned around the sky a bit aimlessly after that. I tried viewing with the PVS attached to a 3x lens using the mirror mount, but the filters placed in between the PVS and the lens are very vignetted, with the outer ~20% dark. The view is too distracting and I think I prefer the 60mm f/6 refractor's view better, even if it is a smaller FOV.
I then tried out the C8. Fortunately, it came to focus even with the filter wheel, so I could, with some awkwardness, move the NV stack to this scope, but would need to rebalance the whole. And to my surprise, the view was not grainy as I feared, given the long focal length. I proceeded to observe a series of globular clusters in the central Milky Way, and also dark nebula, all of which reminded me of what I could see with my 20-inch in a dark sky. The FOV is a little more than 1°, which is big enough the object doesn't move too fast out of the FOV (though a tracking mount would be better). I can see the 4-inch refractor and the C8 as a "lightweight" portable set-up, for times when I need something smaller, rather than the Ayers scope which is heavy and awkward. I think the Ayers scope is more versatile (no swapping of stacks), but I have yet to test how it looks barlowed. In any case, it was pleasantly surprised with the C8.
I decided to see what the C8 could do with some smaller, fainter nebula, so I pulled out Vogel's "Large Planetary Nebula" Observing guide. These are "large" in the context of viewing with his 22-inch telescope, with a similar 1° FOV. I had some very good results with my smaller scope:
Yerkes McDonald 16: =PN G038.7+01.9, 18 54 57.30 +06 02 31.1. At 30x with the C8 with a dual band Ha+OIII filter, I saw a very faint, weak, small oval sky brightness change off the base of a distinctive "L" shaped asterism, somewhat brighter on the eastern side, but no defined edge and no detail within the oval. The nebula is roughly 5'x3' with PA NE-SW. Vogel was unsuccessful visually with 22-inch scope, 7mm exit pupil, and H-beta filter. Kent Wallace was also unsuccessful visually with 20-inch, but he notes Jack Marling had the first known visual observation sometime in 1990 (with an 18-inch?). DSS Image:
Capellaro-Turatto-Salvadori-Sabbadin (CTSS) 3: =Sh2-78. 19h 03 08 +14 06 57. 11'x9' PA NE-SW. Extremely vague oval nebulosity in between two near equal magnitude stars, with dual band filter only. Vogel reports "extremely faint" with 22-inch.
IPHASX J205013.7+465518: 20 50 05 +46 52 48. 6' diameter. Brighter knot in and irregular, curved glow orientated N-S, with mottling in the glow and a brighter southeastern rim. Seen only careful matching of the star field with the finder chart. Vogel successful with 22-inch 100x and OIII. INT/WFC Photometric H-alpha Survey extended sources.
Abell 74: PK 72-17.1 2 21:16.9 +24 09 15.8 871, 791': Extremely weak, subtly mottled round glow, soft edges. C8 & dual band. Wallace unsuccessful with 20-inch, Vogel successful with 7mm exit pupil and UHC, "large and extremely faint glow. Some parts of the edge were well defined."
Motch-Werner-Pakull (MWP) 1: 21h 17 07 +34 12 40, 13'x9': Very small, very faint, curved glow, lying at the center of a trapezium asterism which guided me to the correct location in the field. Vogel successful with 22-inch, " 200x with OIII, an extremely faint, very diffuse and oval patch could be observed at the location that appears brightest on the blue POSS. Other OIII emission regions in the E and W lobes are somewhat fainter."
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