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by Jay Reynolds Freeman
A group of local observers had a late afternoon pot-luck before our observing session at Henry Coe State Park, near Morgan Hill, California, on 2 October, 1999. The food was a great success -- lots to eat, and plenty of variety, even for vaguely vegetarian types like me. Sky conditions were not encouraging; California had several active forest fires, so many that we could not decide which one was causing all the smoke. With an hour to sunset, the solar disc was already reddened, and was surrounded by the sparkly scattering of fine particulate matter. Gray-white clouds visibly lifted ten or fifteen degrees above the horizon in all directions, and milky, washed-out sky indicated the presence of smoke at higher elevations as well. Several of us, including me, were out mainly for deep-sky work, and did not set up. Yet there were telescopes and good company, so we stayed.
As twilight deepened, the smoke made itself felt in astronomical terms: The greater Sagittarius star cloud was all but invisible to the naked eye, and even the lesser one, at higher altitude, was far less bright than the Scutum cloud. Nearby cities made the smoky cover a source of light pollution as well as of reduced transparency, too.
Early evening gave us a chance to look at smoke of a different kind. At 7:01 PM, local time, there was a solid-fueled ICBM launched from Vandenburg Air Force Base -- a test vehicle for an anti-missile system at Kwajalein Island in the Pacific. Its brilliant white exhaust trail climbed rapidly out of the murk at the southern horizon, showing puffs and occasional sparks with staging and other events. The trail remained visible for many minutes, twisting in the high-altitude winds.
Jupiter had not cleared the tree line to the east, and Mars was well down in the last of dayglow, so many observers killed twilight time looking at double stars. I don't think any of us would have bothered with eta Cas if local champion of astronomical whimsy Jane Houston had not dubbed its noticeably reddish companion "The Pink Bunny", but now we all know where it is and will inflict this delightful perversion of IAU naming conventions on many generations of curious public yet to come. There are eight stars in this busy multiple system, but the obvious pair is the two brightest components, magnitudes 3.4 and 7.5, now separated by about 13 arc seconds, easy and colorful in just about any telescope. Of course, now that we have a Pink Bunny, political incorrectness demands that we also have a blue one. I recommend epsilon Boo. Jane, are you listening?
Seeing was very good, even for the largest telescopes present, so we turned to a more difficult target, gamma Andromeda. The AB pair is an easy 10 arc-second separation, but B is itself a double -- its companion is C -- and a tough one for amateurs. The magnitudes are 5.5 and 6.3, and the separation is now about 0.4 arc seconds. I split it last month in my C-14, but rather unsatisfyingly; seeing had broken the image up into several slowly moving speckles, and each one was systematically double. On this night, seeing was much better. An Astro-Physics 180 convincingly elongated the star at about 500x, even while it was still rather low, and somewhat later we snuck up on it in an 18-inch Obsession. At 400x (5 mm Vixen Lanthanum LV) the most I could say was that BC was elongated and occasionally necked, when seeing settled. One enthusiast had a 4.8 mm Nagler stuck into a 3x Barlow, and since the mood of the hour was whimsy, we decided to see what 1250x would show. It was too much magnification for the seeing -- the image was quite active. Nonetheless, gamma And BC was in fact split, and we all had the experience of using over 1000x usefully in an amateur-sized telescope.
The I-can't-believe-it part of this occasion was not separating it, nor even tracking it -- Dobsons do require a rather light touch at 1250x -- but finding it! I had thought that someone had dropped in a lower-magnification eyepiece, and naively stepped to the TelRad and lined up gamma. The star was centered when I got to the eyepiece, and though I thought the seeing looked jittery for 400x, it was several minutes before I realized we still had the Barlowed Nagler in use.
A little later we tried some interim magnifications. The 5 mm LV with a 2x "Big Barlow" yielded a cleaner split at 800x than the one at 1250x. Best of all, in my opinion, was the view at 670x, using an old Celestron 6 mm Orthoscopic with a Celestron 2x Ultima Barlow. Seeing settled frequently at these magnifications, and when it did, there was plenty of dark space between B and C.
With good seeing and poor transparency, planetary targets were the vogue, and as Jupiter and Saturn climbed up the eastern sky, we turned more and more to them. Even the large Dobsons were performing well, and a late-model Astro-Physics 180 mm f/9 EDT was on the field, so many of us were eager to reopen the vexing and inconclusive can of century-old worms labeled "refractors versus reflectors". We did not run a formal comparison, but there were lots of observers taking alternate looks through lots of telescopes, and talking about what they saw. This is always an emotionally-charged topic, since we are all good friends, yet we all like our own telescopes, so let me review some of the problems in making these comparisons before I discuss my own observations. And let me also stress that the fact that I report here doesn't mean that I am particularly qualified; it merely means that I am particularly verbose.
The main problem, of course, is scanty data. Everyone agrees that larger telescopes are more adversely affected by seeing, and more often so, than smaller ones, and that even in coastal California, it is uncommon for 18-inch telescopes to encounter seeing conditions which do not continuously limit them. On this night, seeing was good for the big iron, but not completely constant. Thus even with rapid alternation of views between the different telescopes, we could not be sure of having had equally good seeing with each, and therefore the comparison results may be more erratic than if constant excellent seeing had obtained. Furthermore, in such conditions, there is a statistical bias in favor of whatever telescope you observed with most, for you are more likely to get an interval of fine seeing at whatever eyepiece you look through longest. In such conditions, it would not be remarkable if two equally skilled observers, using absolutely identical telescopes, looking at the same object, each occasionally looking through the other's instrument, both reported that their own telescope was better.
Several of us did a lot of alternate viewing, going back and forth from one of the several 18-inch Obsessions to the AP 180, trying many magnifications. Both telescopes seemed to deliver the best views of Jupiter at 400x or 500x, using the eyepiece combinations I have already mentioned. (We did try 1250x in an 18-inch on Jupiter -- it was *not* an improvement over 400x, but it was fun to try.)
The AP owner had a Zeiss binoviewer almost constantly in use. The 18-inch used single eyepieces. Most observers report that binoviewers markedly improve ability to see detail, but I have never had that experience. Yet on this night, I fussed with interpupillary distance, and jiggled the eyepieces up and down in the focus tubes, and reached a point where the binoviewer was at least not a disadvantage. Chatting with other observers suggested I could see all the detail they could, but even so, my reaction to the binoviewer clearly puts me in a minority, and may bias my observations in some way I do not understand. (Part of my problem may be that the Zeiss binoviewer, like most others, is a difficult design to use, in that it provides no precision adjustment for differential focus between the two eyepieces. Zeiss's optical and mechanical fabrication is first-rate, which makes it all the more inexcusably incompetent that this thousand-dollar-plus unit lacks a feature standard on tacky third-rate mass-market binoculars.)
The planet cooperatively offered fine detail at many contrast levels. There were white spots and streaks in both equatorial belts, providing relatively high contrast against the darker and obviously reddish-brown belts themselves. The equatorial zone -- spanning Jovian latitude zero between the belts -- was strewn with much lower-contrast features, white-on-cream gyres (or perhaps cream on white) suggesting the view down through several layers of swirling terrestrial clouds.
To my eye, the best views of the high-contrast features through the 18-inch were a great deal better than the best views of the same features through the AP 180, and those views came often. Through the 180, I could see the spots and streaks, but the 18-inch gave me a much more detailed view of the scallops and filamentous structures at their edges and in between them. I believe that one or two observers agreed with me on this point, but several did not.
On the other hand, to my eye, the views of the low-contrast stuff through the two telescopes were about equal; I refer in particular to the swirls in the equatorial zone. I didn't hear anyone express the opinion that the Obsession was outdoing the AP in this regard, and I recall that the AP owner believed that the AP was doing better.
We all saw different Jupiters: Often the question, "Did you see ___?", would be answered "No", not because the feature was undetectable, but because the observer had been looking at some other part of the planet. Thus talking with one another much enriched the observations. When I first started looking at Jupiter, my eye was drawn to the high-contrast stuff simply because high contrast made it easy to see, and it was some time before other folks reminded me that I ought to compare low-contrast features as well. If I had not done so, I might have gone home thinking the 18-inch Obsession outperformed the AP 180 across the board. Yet that was not the case.
So to my eye, on this night the big Obsessions were rather the preferred telescopes for planetary viewing, because they did outperform the smaller, high-end refractor at least on high-contrast detail. Your mileage may vary, particularly if you are looking at a target which does not have any high-contrast detail, or if you seriously miss a sidereal drive, or if your observing conditions do not permit a wide split of gamma Andromeda BC, or perhaps just because you are not me.
Later in the evening, the attention of many turned to Saturn. I am most greatful to the owner of the AP for the opportunity to make a long observation at 600x (Zeiss binoviewer, 3x Barlow, 10 mm Zeiss Abbe Orthoscopic eyepieces -- the binoviewer itself increases magnification 20 or 25 percent). I will report it here, quoting from my log, as an example of what one may see with a superb instrument in superb conditions. (And I won't identify the owner, out of long tradition of not broadcasting to the Internet the names of folks whose garages contain lots of expensive stuff. But thanks anyway.)
The A ring is brightest just outside the Cassini division, then its intensity declines to a minimum at about the 50 % position, the division formerly known as Encke's, which I see as a not quite sharp line. Brightness increases radially outward again, but the outer periphery of the A ring is not as bright as the inner. There is a hint of another fine gap or division at 80 or 90 %, which would be the Keeler Gap if seen, but I can at most log it as suspected and cannot rule out a diffraction effect at the outer edge of the A ring.
I cannot see the planet -- disc or edge -- through the Cassini division.
The outer portion of the B ring is the brightest part of the ring system. Its brightness holds roughly constant in till about the 60 % or 70 % position, (taking 0 % as the B/C edge), then shoulders off and declines smoothly to the B/C interface. The C ring is markedly dimmer than any part of the B ring. B-ring brightness variations are most apparent in the ansae. I looked for B-ring "spokes" but saw none.
The Planet's disc has a wide, nearly homogeneous brown band that covers most of the south temperate latitudes. The band appears slightly more intense on the morning side of the central meridian, at least at about 0600Z 3 October 1999 it did. The south polar cap is set off from the south temperate band by a lighter zone. The cap appears darker and more neutral in hue than the band.
The shadow of the planet on the rings is prominent.
We tried 1000x in the AP 180 on Saturn, too -- using 6 mm Zeiss Abbe Orthos instead of the 10 mm units. That magnification made the suspected Keeler gap a little more easily seen, but improved no other feature, at least, not to my eye.
The 18-inch Obsession, at 400x and 570x, also offered good views of Saturn. I did not spend nearly as much time looking at Saturn with it as with the AP 180, but I did note the suspected Keeler gap with the Obsession. A C-11 at perhaps 300x was not doing as well on Saturn as either the 18-inch Obsession or the AP 180, though it did show the 50 percent minimum in the A ring.
Still later in the evening, some of us looked at a few Messier objects in the Obsessions. I went home not long after Moon rise. It had been a surprisingly interesting night for so much sky obscuration.