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John Boudreau
scholastic sledgehammer
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Reged: 04/06/08

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Re: Hexagon, possible? new [Re: Chuck Hards]
      #5983742 - 07/21/13 10:11 PM

The polar hexagon is currently *just* under 4", at about 3.8 to 3.9". When near the CM a 'flat' of the hexagon is about 2" long. This is based on the current 17.1" equatorial diameter of Saturn from WinJupos, and some measurements of recent images I've taken.

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.


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azure1961p
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Reged: 01/17/09

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Re: Hexagon, possible? new [Re: Chuck Hards]
      #5983830 - 07/21/13 11:19 PM

Chuck I think you are merging that central vortice with the hex. David's diagram amply shows the hexagon shape as that dark polar spot. The hex isn't within that but that is it in its entirety. Now within that in the dead center - that's another phenomenon I don't think any observer can possibly see with any scope that central vortex . Though CCD is something altogether different.

Pete

Edited by azure1961p (07/21/13 11:20 PM)


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David Gray
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Reged: 08/06/12

Loc: Co. Durham UK
Re: Hexagon, possible? new [Re: azure1961p]
      #5984069 - 07/22/13 07:05 AM Attachment (15 downloads)

It became evident to me a while back that some of us were talking of different things. In particular when I see a statement claiming to see the “hexagon” but not the hexagon shape: i.e. they have seen the North Polar Cap (NPC).

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!

Dave.

Edited by David Gray (07/22/13 07:20 AM)


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Chuck Hards
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Reged: 05/03/10

Loc: The Great Basin
Re: Hexagon, possible? new [Re: David Gray]
      #5984096 - 07/22/13 07:44 AM

Well, when I'm wrong, I'm wrong. I concede my error after doing a bit more research. The dark cap we see in the telescope does seem to demarcate the edge of the hexagon.

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:

http://www.planetary.org/blogs/guest-blogs/2013/0201-fletcher-saturns-hexagon...


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dscarpa
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Re: Hexagon, possible? new [Re: TG]
      #5984740 - 07/22/13 04:34 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

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idp
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Reged: 08/21/09

Loc: New Haven, CT
Re: Hexagon, possible? new [Re: dscarpa]
      #5988027 - 07/24/13 03:57 PM

Quote:

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?

Regards,

Ivano


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David Gray
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Reged: 08/06/12

Loc: Co. Durham UK
Re: Hexagon, possible? new [Re: idp]
      #5989125 - 07/25/13 08:39 AM

Quote:

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.

Regards,
Dave.

Edited by David Gray (07/25/13 08:41 AM)


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Chuck Hards
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Re: Hexagon, possible? new [Re: David Gray]
      #5991928 - 07/26/13 08:29 PM

Quote:

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.


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