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by Matt Tarlach
Another great Lassen weekend! I went up with my friend Ken Sablinsky this time, as the wife got her fill of cold high altitude nights in July. We observed Thursday and Friday nights - the first offered very good sky conditions, the second was trying yet satisfying. Here's a recap, as brief as I can make it:
Thursday evening clouds threatened to the South, yet never advanced to the observing site at Bumpass Hell. It's impossible to A-B compare nights a month apart, but I don't think skies were quite as dark as either of the nights I observed from Bumpass in July. Still fine, though, and very good seeing that got better as the night went on! As twilight deepened, I started with some double stars. Antares split easily in my 12.5" f6 Astrosystems dob with Swayze mirror. At 315x (6mm Radian) there was plenty of black space between the brilliant orange-red primary and the faint, drab, greenish-white companion. Alpha Herculis was a tight, pretty double, with a coppery primary and sapphire blue companion.
As the darkness deepened, I visited some old favorites along the summer Milky Way before turning to the "hit list" that I'd prepared for the weekend. One of the most enjoyable objects I'd targeted was a dark nebula, Barnard 142-143, which was featured recently in one of the magazines. Known as Barnard's "E," it really does look just like a black capital "E" superimposed on the bright Milky Way field near Altair. We enjoyed the view several times over the two nights, in 8x42, 16x80, and 25x125 binoculars.
I revisited Seyfert's Sextet, which I had first detected back in July. This time I sketched the tight, mottled glow, and comparison to photos shows I detected 4 of the member galaxies. Then followed a galaxy hop through Draco to one of my priority objects for the weekend: Markarian 205. This quasar, with an estimated distance of 1.3 billion light years, is the first such object I've observed, and by orders of magnitude the most distant object I've detected. I used the finder chart in the Night Sky Observer's Guide to track it down: at 212x in the 12.5" it was held with averted vision, and glimpsed directly.
As the night progressed we took time out to watch the Perseids, and paid visits to (among others): NGCs 7009 (the Saturn Nebula), 7293 (the Helix), 253 (the bright, dusty galaxy in Cetus), 6888 (the Crescent), and the beautiful edge on galaxy NGC891. The view of the Saturn Nebula was especially remarkable - the ring-like extensions were quite easy to see, and when the seeing steadied bulb-like swellings at the ends of the extensions became visible (at 212x w/ Ultrablock filter). We finished up the deep sky agenda for the evening with the Bubble Nebula, NGC 7635. This was a fairly easy detection as an approximately round mass of nebulosity encasing a fairly bright star, but none of the exquisite spherical structure apparent in photographs was detected.
Perhaps the most interesting observation of the night came late, at about 3 AM, when we turned the scope to Saturn. We had looked at Saturn and Jupiter earlier in the evening, when they were low in the East, and while they were pretty then the best viewing was reserved for those who stayed late enough to catch the planets high in the sky. On Saturn, we started at 315x (6mm Radian) which is the highest power I generally use at lower altitude sites. The view was steady and filled with detail, so I switched to a borrowed 4mm Radian for 475x. We also tried a 3mm for 630x, and Ken preferred that view, but I stuck with 475x for the higher contrast and easier hand tracking. I didn't think any more detail was visible at 630 than at 475.
And what detail was visible! The Crepe ring was obvious, and Ken commented on the apparent "hardness" of its inner edge. Cassini's Division was easily visible all the way 'round. A thin, brown equatorial band was detected, with a thickening or possible festoon-like feature curling southward from the band toward the following side of the planet. The brown color was the richest that either of us had ever seen on Saturn.
A darkening was noted in the outer half of the "A" ring. I sketched it as beginning at about the middle of the "A" ring, and continuing out to about 70% of the ring's radius. Not a black gap like Cassini's, but more of a subtle darkening, it was clearly seen by both of us when the seeing was steady. Encke's Minima, perhaps? I'd glimpsed or suspected this feature before, but never seen it so easily or certainly.
At the outer edge of the "B" ring, next to Cassini's, we noted several bright whitish markings. At least three were visible to the preceding side of the planet, and one to the following side. They were difficult, visible perhaps 20% of the time in the moments of steadiest seeing, but we both agreed on their general appearance and location: right up against Cassini's, whitish, and small, only extending a few arc seconds into the "B" ring.
Since making the observation I've looked at many pictures of Saturn, mostly by the Voyagers or the HST, and haven't found any features resembling these bright areas. I have seen images of dark, diffuse markings in approximately the same location. Now I'm wondering whether our observation was really a contrast effect, as our attention was drawn to the bright segments of the "B" ring between these dark markings. If that's the case, then the indirect observation of the dark markings on the "B" ring was my first sighting of these features.
Has anyone observed similar features on Saturn's rings? Are the dark markings what are known as the "spokes" of Saturn's rings, or if not is there another name to hang on them?
We stared at Saturn until first light, then packed up and headed down to our motel room at Childs' Meadows. The next day (Friday) we hiked down to the Bumpass Hell thermal area. As we returned to the parking lot/observing site, we braced for an even better night, as there was no sign of clouds in the sky and jet contrails were short, suggesting less high altitude moisture and potentially darker skies. Alas, as darkness fell some kind of clouds (perhaps orographic in nature?) began forming above, and the night became touch-and-go.
Among the highlights for me on Friday were M2-9 (Minkowski's Butterfly), seen in Mark Wagner's 18". The two long lobes were visible, clearly separated from the central star (thanks for the view, Mark!). As the clouds overhead thickened, I turned to the only area of the sky open for observation...which luckily was the rich Milky Way of Sagittarius! I checked off several NGC clusters and planetaries that I might not have troubled with otherwise, and wound up with a renewed appreciation of the density and variety of objects in that part of the sky.
As the clouds thickened, most TACos returned to camp. Yet it seemed that every time someone would depart, the clouds would open to reveal their hidden treasures. During the clear intervals I moved up the Milky Way searching out planetary nebulae, including NGCs 6210, 6772, 6778, 6852, and 6804. The last object I logged was the faint but fascinating planetary Abell 70. Viewed through an O-III filter, this nebula appears faint but fairly easy at 212x, round and hoop-like. Viewed without a filter, the nebula nearly disappears into the sky background, but one edge (forgot to log which edge) stands out brightly. This brightness is actually the light of a distant galaxy, which shines through the nebula! It is a unique and remarkable object, and a fine way to close out the night and another great weekend of Lassen observing.