It was a great observing experience last weekend spending two days/nights in a pristine Sierra setting under remarkably dark skies with several deep sky addicts. Over the weekend of August 21-22 observing partner Jim Shields as well as Mark Wagner, Marsha Robinson, Richard Navarette and Ray Gralak caravaned up to the Sierra Buttes above the Gold Lakes basin in Plumas County. Packer Saddle is the official observing site of the week long "Introduction to Observational Astronomy" class offered at the Sierra Nevada Field Campus of S.F. State University which Jim and I have been teaching assistants for over 10 years. So we were well aware that except for a small glow low in the southeast towards Reno and another low in the southwest from Grass Valley/Nevada City this was a startling dark site at 7200' elevation with a great vista of the Sierras in all directions!
Taking advantage of the observing conditions, I bypassed the brighter NGC fare and went to work on lesser known targets which require transparent skies. Here's a rundown of most of the objects I observed with my 17.5" -
Globulars:
Palomar 11 is located in southern Aquila just 5' southeast of a mag 9 star. At 100x it appeared as an irregular diffuse glow nestled to the SW of a group of mag 12/13 stars. At 220x, it appeared nearly 4' in diameter and obviously mottled. Several faint stars were resolved (or superimposed) with averted vision over a ragged glow.
Palomar 12 was also easy to track down as it is situated close NNW of a distinctive trio of mag 11-12 stars. The globular was an irregular 3' glow at 220x, with very three very faint mag 15 stars superimposed on the diffuse background glow.
Mayall II is the brightest globular in M31 and really the only globular I've observed in M31 (of about 20) which is clearly nonstellar. It appears as a fuzzy mag 13.5 object ~10" diameter with a bright quasi-stellar nucleus. The view is confused by a mag 14.5-15 star at the SW end and a fainter star at the NW edge of the halo.
Planetaries:
Abell 39 is a large but little-known 3' planetary in Hercules the was picked up 100x using an OIII filter sweeping the field. Once identified it was visible continuously with direct vision as a round, sharp-edged disc which was slightly brighter on the following edge. The planetary was even faintly visible without a filter and several faint stars were seen to be superimposed.
Next on my observing list was Abell 65, one of the relatively bright Abell planetaries situated in Sagittarius. The oval glow (about 1.5' major axis) was noticeably elongated NW to SE with a mag 13.5 star placed at the SE tip. The surface brightness seems to fade into the background as you move towards the NW end. Again this planetary was visible without a filter at 140x, although the view was more pleasing with an OIII filter.
A little later in the evening I tracked down a much more difficult low surface brightness planetary, Abell 74, in Vulpecula. Of special interest is a tiny mag 15 galaxy (CGCG 471-2) which shines through the dim disc of the planetary. The planetary itself is just an extremely weak glow in the milky way using an OIII filter at 100x, at least 10' in diameter.
Sharpless 2-71 (originally catalogued as an HII region) was immediately picked up 100x using an OIII filter just casually sweeping the area. This is definitely a "showpiece" obscure planetary in dark skies and I pulled the rest of the observing group over for a look. 140x provided an excellent view as this 2' planetary (elongated N-S with a brighter northern end) appeared mottled with a noticeably irregular surface brightness.
The final treat was one of my favorite planetaries, Jones 1, which is located in Pegasus. This huge annular planetary (nearly 5' diameter) has a distinctive "C" shape open at the E end with a very dark center. The planetary is dominated by two relatively narrow bright arcs in the rim along the NNW and SSE sides which are faintly connected along the W side.
Bright Nebula:
Minkowski 1-92, the "Footprint Nebula", has a bipolar appearance and was originally classified as a reflection nebula. More recent investigations of the central star has reclassified it as a young planetary or protoplanetary category. Visually, this object appears as slightly out of focus mag 12 star at 220x, located just 2' SSW of a mag 9 star. The "Footprint" nickname is from the very small (4"-5") bright knot (the "Sole") which is attached to a very faint and small extension to the east (the "Heel"). This object is very difficult to find at low power due to its small size and rich milky way field.
IC 5146, the "Cocoon Nebula", is a fascinating object due to structure in the emission nebula and the long dark lane (Barnard 168) which extends a full degree to the west. The Cocoon is also in a small group of objects which benefits from an H-Beta filter. It has an irregular round shape ~10' diameter with a very irregular surface brightness (dark mottling and brighter regions) and an extension or stem on one end. Several stars are superimposed including a couple of mag 9.5 stars.
The "Elephant's Trunk" (vdB 142) is an unusual cometary globule (associated with star formation) on the west side of the huge but faint HII complex, IC 1396. The most contrasty view was at 100x using a UHC filter, where a 15'x5' lane was evident, particularly by rocking the scope. The "tail" of the globule or elephant's "trunk" trails to the west and is weakly illuminated on the edges, particularly on the south side. A pretty double star is embedded in the lane which shows variations in width and opacity.
Barnard's galaxy (NGC 6822) is a well-known amateur target in Sagittarius but lesser known are two prominent HII knots which easily showed up at high power on the north edge of the galaxy. These are catalogued as IC (or Hubble X) and Hubble V. Much more difficult was Hubble III which appeared as a stellar spot off the NW side of the galaxy.
Galaxies and groups of galaxies:
Abell 76 was original catalogued as a regular, symmetrical planetary in Aquarius but it was shown in 1971 to have a radial velocity of ~3425 km/sec and more recent analysis has shown it to be an unusual collisional ring galaxy with line emission. At 220x a very faint oval glow was picked up 2.5' W of a mag 9 star, perhaps 30" in diameter but there was no indication of a ring.
The WLM system (dwarf member of local group discovered by Max Wolf, Knut Lundmark and P.J. Melotte) is a difficult low contrast galaxy in Cetus, but in these dark skies was picked up without much difficulty while sweeping at 100x. This unusual galaxy is large, ~10'x5', elongated N-S without the usual central concentration and with a very low surface brightness. Jim and I had hoped to observe a 16th magnitude globular cluster which was situated just off the west side near a 15th magnitude star. The star was clearly visible but the globular was only suspected for fleeting moments.
ARC (Abell Rich Cluster) 3744 in Capricornus contains three faint NGC galaxies - 7016, 7017 and 7018 within 3'. Much more challenging was 16th magnitude MCG -4-49-16 to the NE of NGC 7018.
ARC 2593 in Pegasus contains only one NGC member - 7649, but with averted vision Jim Shields and I picked out three anonymous members within a few arc minutes. These all appeared less than 20" in diameter and required averted vision to confirm.
Hickson 81 is a very compact quartet of 16th and 17th magnitude galaxies, also catalogued as UGC 10319. The combined glow of one or more of these galaxies was just visible as a very soft glow - at steady moments it appeared double but just detecting this distant cluster was satisfying.
Zwicky's Triplet or Arp 103 is an interacting trio with a thin bridge connecting a close pair of galaxies (UGC 10586) with a companion 2.5' northeast. The brightest member was not difficult, appearing as a 30" round glow with a small brighter core. The companion NE was much more difficult, requiring averted vision and appearing as a 15" weak glow. On closer inspection, the main component was noticed to be elongated and with concentration a faint companion was just resolved at times off the WSW side.
After tracking down these challenging but satisfying targets, I crawled into my sleeping bag at 3:00 AM both nights happily exhausted.