Posted 07 July 2013 - 01:42 PM
Just to check:
Using WinJUPOS I have determined my transit for the SP feature as L3 = 311.5. Schmude’s drawing CM3 = 128 deg; eye-estimating his feature at L3 = c.170 deg. I make our obs. as 10 days apart – you said 2 months so wondering if a mistake somewhere?? A second feature is a possibility assuming no error of course; even a lighter stretch of the SSTZ defined p. & f. by similar dusky features but nothing catches my eye in a rather hasty check; but a fair number of SSTB darker sections etc. However my int. sketch for 1999 Feb. 24 18:20 UT shows two n.edge undulations on the SPB and indicated “!!” and eye-estimated at L3 = c.290 deg.
From all this we might assume that certain SST/SPR activity might delude us into a hexagon interpretation. Then coming to this apparition I have seen a few comments claiming lighter patches in the already lighter NPR. So, turning things around, are the broader NPR (NPCs to NPBn) parts twixt the hexagon vertices being (mis)interpreted as discrete NPR features – seeing and lack of resolution possibly compounding things??
Posted 07 July 2013 - 07:43 PM
Just to check:
Using WinJUPOS I have determined my transit for the SP feature as L3 = 311.5. Schmude’s drawing CM3 = 128 deg; eye-estimating his feature at L3 = c.170 deg. I make our obs. as 10 days apart – you said 2 months so wondering if a mistake somewhere??
Of course, on my part. I read the "2013 07 07", so I thought "July 7th", but of course it was 1998! Apologies, I always have to do these things on the run and this morning it was no exception.
Posted 09 July 2013 - 01:32 PM
Possible? I have had several fair sightings this apparition so I would say yes - at least incipiently definable I venture to say! The current light surroundings (NPR) of the NP Cap perhaps giving rather unusually ideal circumstances. Details with attached recent observation.
Superb sketch, David. I'm glad you made it out. As you say, the primary problem seems lack of contrast, not resolution (since even 8-inchers have resolved it in images). Saturn is so low now that it's hard to make out even Cassini from my latitude (47-d). I'm amazed that you can see so much from the UK though you do apparently have a giant custom made aperture.
Posted 10 July 2013 - 06:13 AM
Yes I am pretty well persuaded that the NPC hexagon is definable in apertures less than my 415mm D-K in the very best conditions, especially given the contrasts prevailing this apparition. I had hoped to use a 152mm off-axis stop in such circumstances but now I’ve just about lost Saturn over the rooftops by good darkness. Had it occurred to me: as the D-K has only a 19% CO (optical window – no vanes) I could have constructed some 200mm – 300mm on-axis masks and still had a CO fairly close to commonly used SCTs etc, and which might have proved informative!
A pity to lose Saturn as we have a stable high pressure over the UK now. But yes I do fairly often get good seeing low down with my apparently ‘anomalous’ local microclimate at this latitude of +54.7 deg.! In fact of late I have seen Antares B (3 nights) with ease and its at an altitude of 9 deg. here and Antares is usually just a >5” blur – the atmospheric dispersion is always gross however and have no means of reducing it below c. 15 deg.( dec.-20 deg.)- apart from stopping down of course.
I perhaps can give another indicator of a hexagon effect as on July 8 with the seeing not quite up to it I got the effect of a dark spot on the NPC which, pending checking, may well be a vertex of the hexagon – somewhat past the CM at 21:20 UT.
Yes the 415mm f/16 D-K is custom made (1977/78): optics by James Muirden, mechanical by Peter Drew. Guests have described it as giving refractor-like performance without the chromatic drawbacks, some of whom have used large/r refractors. It was last recoated in 1989 by the late David Sinden himself (formerly of Grubb Parsons). I was with him to watch the process; thanks to his skill (and the optical window) the coating still looks fresh and continues to go well past mag. 16 on a decent night (15 with the binovu). This tribute-site shows him in the very workshop where he coated my mirrors: https://sites.google...me/david-sinden - the casual ease the way he handled my mirrors actually caused me some concern which amused him greatly when he saw the look on my face!!
Posted 11 July 2013 - 02:26 PM
Posted 20 July 2013 - 11:35 PM
Correct me if I'm mistaken, but isn't the hexagon about half the diameter of the cap (or hood) itself? So any apparent faceting of edges of the cap itself could be chalked up to the power of suggestion?
Our club has a 32" Cassegrain (812mm) and I plan to try for the Hexagon at my next opportunity. As others have noted, the best seeing may have to wait until next year, when Saturn is in the early morning sky. Right now the evening seeing is terrible from my area.
Posted 21 July 2013 - 09:14 AM
Posted 21 July 2013 - 01:36 PM
I'm not going to disagree, I hope to see it myself, but it's a lofty goal.
Saturn is only about 20 arc seconds in diameter (rings are about 49 arc seconds) so the hexagon is probably less than 1.5 arc seconds across, at best, probably closer to 1 arc second, so any telescope used would have to be able to resolve sub-arc-second features. Saturn is nowhere near opposition now so the hex may be even smaller. It's also a low-contrast feature, being buried in the polar hood, both darkish features.
Secondary obstructions will work against us when trying to discern low-contrast planetary details. Fast Newtonians and most Cassegrains have very largish secondary obstructions, and it's a rare large-aperture light-bucket Newtonian mirror that is considerably better than diffraction-limited. And unfortunately extremely large APO refractors are non-existant. Even our club 32" Cassegrain has a 10" secondary, and fairly thick steel support vanes.
I'm thinking that a large Mak may have the best chance of seeing the hexagon, along with superb transparency and a very steady atmosphere. Large Maks (say 12" and higher) are a rare breed as well.
But let's keep trying, I plan to.
Posted 21 July 2013 - 03:55 PM
Saturn is only about 20 arc seconds in diameter (rings are about 49 arc seconds) so the hexagon is probably less than 1.5 arc seconds across, at best, probably closer to 1 arc second,
With respect I have to differ with these dimensions for the NPC/Hexagon. Attached is a graphic to scale after some recent imagery (rather than use my drawings with any inherant innaccuracies!).
Here this is based on an equatorial Saturn diameter of 17.2" and Jupiter at 35" (Equatorial). As I suspected the NPC comes out similar angular size to the GRS.
Posted 21 July 2013 - 08:36 PM
Posted 21 July 2013 - 09:11 PM
So the hexagon is certainly large enough, but I think the trick is to detect how far the vertices of the hexagon project vs. what would be the edge of a hypothetical 'smooth' polar region, and of course those are only fractions of an arcsecond. But the contrast between the dark hexagon and it's brighter immediate surroundings is strong, which certainly helps. I believe this within the range of David's scope and his visual skills. Possibly even with a somewhat smaller scope in excellent conditions.
Posted 21 July 2013 - 10:19 PM
Posted 22 July 2013 - 06:05 AM
Over the years there has been a lot of confusion with the polar regions: e.g. a very dark S/N Polar region being described as a very large S/NPC (or Hood); particularly if the Cap-proper is not detected. In general the edges of the NPR & NPC are near latitudes +60 & +75 repspectively.
Pete, Polar Vortexes: the NPC one may well be beyond visual - being similar in size to Rhea’s shadow which is often difficult against a much lighter background than the NPC usually offers. The SPC Vortex I believe has been spotted, perhaps at least as far back as Lassell in the mid 19th century. Several, including me. have drawn dark (and sometimes light) spots centred on the S Pole: this storm being considerably larger than Titan.
Back in the 1960s-70s I have on occasion described the SPC as variegated (10” Newt.) as have others. As we can see from Cassini imagery these regions are very dynamic and perhaps on occasion the relative contrasts are more accommodating!
Anyhow we’ll not see the S. Pole for some years; but next apparitions the NPC will be increasingly better presented tho’ the planet not favourably placed for many north of the equator sadly! Also will the unusual surrounding NPR lightness endure? I have thought it already progressively duller in the later weeks of this apparition.
To avoid ambiguity each year I include a diagram adapted from one of my drawings with my end-of-apparition report to the BAA, a copy is here attached. I happen to have this to hand, being done earlier for another enquirer!
Posted 22 July 2013 - 06:44 AM
The good news is that it's not as small as my pessimistic first thoughts.
I also found this while web surfing the hexagon subject, it may be old news to some of you:
Posted 22 July 2013 - 03:34 PM
Posted 24 July 2013 - 02:57 PM
The hexagon was a lot smaller and darker than the cap. When the air was a bit unsteady it looked like a small dent in the top. Saw it again in my C9.25 and IM715 last week. David
Uh? I don't understand, both in CCD images and drawings it clearly coincides with the NPC. Indeed, it IS the NPC that happens to have that particular shape.
David is right, we should all remember and use the good old standard nomenclature, especially visual observers. But I fear it won't happen.
By the way, David: sorry for the OT, but I noticed you sketched Encke/Keeler as a rather broad darkening of the outer edge of the "classic" Encke. That's how I happened to see it once or maybe twice with my old 8" newton (rings wide open and great seeing, to be sure). May it be just a contrast phenomenon, rather than having to do with the actual gap?
Posted 25 July 2013 - 07:39 AM
By the way, David: sorry for the OT, but I noticed you sketched Encke/Keeler as a rather broad darkening of the outer edge of the "classic" Encke. That's how I happened to see it once or maybe twice with my old 8" newton (rings wide open and great seeing, to be sure). May it be just a contrast phenomenon, rather than having to do with the actual gap
Encke/Keeler: my own feeling on the contrast issue is that one enhances the other to a degree. We know we have a real feature mingled with this and I suspect if there were no division the sky/ring contrast ‘interface’ would be the weaker therein. I have seen it darker and sharper than shown here but never as a thinner version of the Cassini. Touching very slightly on my Uranus in twilight thread: my finest views of the division were in twilight with near perfect seeing when Saturn was at high n. declination. Here we have the sky not a stark black against the ring edge surely minimizing/muting any contrast effects.
OT ( this not my thread of course): I never want to come across as pedantic on this. It would be a shame if the rules were to be applied so rigidly that it were to detract from the richness of discussion. It is one thing, as you have done, to go down a ‘side-alley’ of the planet in discussion as opposed to going into warp-drive to the inner part of the Solar System!
If we were to hair-split then I may well be guilty too and indeed have even expressed my concern in that regard on the recent Cassini div. thread when it diverted to apodizers!
Slyly taking it back to the hexagon (!) I think contrast is a factor there too. I have never recorded the intensity of the edge/rim of the NPC as dark (8.5) as at this apparition and feel some of this at least is down to the unusually bright NPR- surround.
Posted 26 July 2013 - 07:29 PM
Touching very slightly on my Uranus in twilight thread: my finest views of the division were in twilight with near perfect seeing when Saturn was at high n. declination. Dave.
Apropos the fine seeing at twilight comment- When SL-9 hit Jupiter in '94, I noticed that the best seeing was after sunset but with a still bright sky- very blue. Many times during those observing runs, there was a brief period of exceptional stillness of the air, lasting anywhere from 10 to 30 minutes, after which the turbulence returned for several more hours. I was using a 10" f/5.6 Newtonian and the air was so still that I could run up the magnification to over 400X at times, with no degredation. I've heard it explained that after sundown, there can be a period of thermal equilibrium between the air and the ground, but it is temporary as the ground soon begins to release the thermal energy it accumulated during the day. Since then I've noticed it on other planets and the moon on many occassions. When it happens, it is extraordinary, as if the atmosphere almost disappears. Incredible sharpness for an all-too-brief period.