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azure1961p
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Enckes
      #5782909 - 04/06/13 11:57 PM

I've not yet seen Enckes with my 8" reflector, but Ive never seen the rings fully open with that scope, infact now is as wide open as that scope has ever seen them and despite 9-10/10 seeing, not even a dither.

That aside others have and in that is the point of the thread. I was wondering how Enckes thresholds or emerges into resolution . There seems to be an either-or understanding of its visibility nature. Either you resolve it as a thin grey line or you're out of luck.

But I wonder if its a little more subtle than that...

The outside edge of the A ring from Enckes, past Keeler to the absolute edge is actually lighter in tone than the rest of the a-ring. Might this albedo difference, albeit, slight , be visible even if the Enckes gap isn't seen linearly? Asbytec (Norme) claimed at one point he might have seen Enckes and it was met with some countering and he infact wondered if it were a diffraction effect or the minima effect (If I recall).

But is it that ?

What if he observed the outer edge of the A-ring to be slightly brighter than the rest - could this be less diffraction effects but more inline with not seeing the gap/line but seeing a brighter edged A ? If its fringey enough, the brightened rim of the A could be seen to have a curiously dithered look as it wavers in and out of resolution. Enough perhaps to trigger at least a question of something there. Too, Ive seen CCD images and drawings where this brightened A edge is shown but not really the Enckes feature.

In the face of this stand a few countering obstacles

1. The diffraction effects that close to the edge would nix any hope of seeing so fine a line in apertures under 10" (seemingly the conventional wisdom).
2. The albedo effect might have a lower contrast threshold than the Gap making it impossible to reason then if Enckes Gap is invisible.

3. The smaller aperture isn't presenting enough light to see the feature at the magnification required to provide enough enlargement to visually hash it out. Generally its been assumed and shown in history that 400x is a minimum.

My position here is neutral to conservative. I have hope that the new sharpness had via boundary layer fan might eek me enough for Enckes afterall.

Thanks in advance

Pete


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David Knisely
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Re: Enckes new [Re: azure1961p]
      #5783039 - 04/07/13 02:20 AM

One night near a favorable opposition (and at over 400x), I just barely glimpsed the Encke division in my 10 inch Newtonian, but not in anything smaller. Even in my 14 inch Newtonian under very good conditions, it can be difficult to see. I once wrote an article about it and concluded that for various optical reasons, it probably won't be visible in apertures a lot smaller than nine inches (I never saw it in my 9.25 inch SCT or my "planetary" 8 inch f/7 Newtonian). Clear skies to you.

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BillFerris
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Re: Encke Division new [Re: azure1961p]
      #5783056 - 04/07/13 02:43 AM

The one time I've been confident of seeing the Encke division was in September 1997 using the Lowell 24-inch Clark refractor on a night of perfect seeing. At full aperture, the image was rock solid steady at 445X and the narrow dark band of the Encke division was visible just inside the edge of the creamy A ring. Here's a link to my notes and sketch of that observation: Saturn in the Lowell 24-inch Clark.

There was quite a lively discussion of the history and challenge of observing the Encke division back in 2004: Seeing Encke

On an historic note, I find it wonderfully ironic that the ring division named after Johann Encke is a feature he never observed, while the gap named after James Keeler, who discovered the Encke division, is not visually observable in any ground-based telescope.

Bill in Flag


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azure1961p
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Re: Encke Division new [Re: BillFerris]
      #5783166 - 04/07/13 06:17 AM

David,

Yes I recall the article well. I was considering the albedo of the outer A ring as the possibility it may at least provide a brightened fringey edge that while not show the division reveals this seperate ring another way through contrast. The archive Bill linked to has this photo by Wes Higgins showing this albedo effect well at the ansae: http://www.cloudynights.com/photopost/showphoto.php?photo=348&password=&a...

Bill, thanks got the lively debate indeed. Edz did a fine job of hashing out the particulars here. Just to reiterate , my theory/query was wether or not the lighter contrast of this outer section of the A ring might have its own pseudo resolution in revealing its presence even though the Enckes is still invisible. While the contrast here is ultimately far lower than Envkes division, its far wider too which I thought might offset that bringing this ring section to visibility even when the associated gap or line was not.

Thanks!

Pete


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idp
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Re: Encke Division new [Re: azure1961p]
      #5792145 - 04/11/13 11:21 AM

Pete, Encke was a regular feature in my 8" newton, provided the rings were open enough and seeing was good. However, I could not spot it clearly with a 10" newton a couple of mornings ago, seeing being about III. Keeler of course is a different can of worms, I never saw it.

I'm using the old nomenclature by the way, not the (confusing) official IAU one.

Steady skies,

Ivano


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azure1961p
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Re: Encke Division new [Re: idp]
      #5792240 - 04/11/13 12:15 PM

Thanks Ivano.

In fairness the best times Ive seen Saturn in terms of 9/10 or better the rings are as they are now. I've never seen optimum presentation with my 8". Long boring story why. It'd be amazing if my boundary layer fan made the difference though and revealed it at its current presentation. It would b a first. As you know the relative rarelty of great seeing in CT is quite seasonal with hot balmy summer nights the best.

Thanks for your comments Ivano.

Pete


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idp
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Re: Encke Division new [Re: azure1961p]
      #5792395 - 04/11/13 01:36 PM

Quote:

As you know the relative rarelty of great seeing in CT is quite seasonal with hot balmy summer nights the best.






Yeah, I'm waiting for the jetstream to choose another latitude but it's been pretty stuck up there lately


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azure1961p
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Re: Encke Division new [Re: idp]
      #5792441 - 04/11/13 02:01 PM

Oh tell me about it. I swear its tethered to my condo. Last good seeing for me was Thanksgiving week - a good 5 nights of it were 7/10. After that between 4-6/10.

In fairness I haven't been out for the last 6 weeks too much but when I was it was moosh.

Lousy weather in general really. And winter seems to not want to let go.

Pete


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David Knisely
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Re: Encke Division new [Re: idp]
      #5792444 - 04/11/13 02:03 PM

Quote:

Pete, Encke was a regular feature in my 8" newton, provided the rings were open enough and seeing was good. However, I could not spot it clearly with a 10" newton a couple of mornings ago, seeing being about III. Keeler of course is a different can of worms, I never saw it.

I'm using the old nomenclature by the way, not the (confusing) official IAU one.

Steady skies,

Ivano




The Encke minimum feature may be visible in smaller apertures (and at relatively modest powers), but the actual ultra-narrow division right next to the outer edge of the A-ring? Well, I have a hard time believing it to be seen in any telescope much smaller than 10 inches. The diffraction effects would tend to make it blur into the darkening of the soft outer edge of the A-ring, making it invisible. As I have said before, as hard as the actual division has been to see in 10 and 14 inch apertures, I don't see it being visible in anything much smaller. Clear skies to you.


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azure1961p
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Re: Encke Division new [Re: David Knisely]
      #5793583 - 04/11/13 11:55 PM

Good points David. The majority of information Ive gathered from reliable successful observers seem to hover around 10" and 400x. When 8" is mentioned its been in the vein as potential limit of lower end aperture some stressing a refractor at that. I see your points and again historically as well but Im guardedly optimistic about nabbing it. Id be interested to hear more on Ivanos take too.

Ivano, are you referring to the Ecke Gap that's about 1/5 the sep of Cassinis or is this the Encke Minima? Thanks.

Pete

An interesting thing David. You mentioned 50mm is about the limit for resolving Cassinis. Enckes being about five times finer would make that threshold aperture infact five times larger than 50mm which is 250mm/10".


Edited by azure1961p (04/12/13 07:15 AM)


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idp
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Re: Encke Division new [Re: David Knisely]
      #5794057 - 04/12/13 09:58 AM

Quote:



The Encke minimum feature may be visible in smaller apertures (and at relatively modest powers), but the actual ultra-narrow division right next to the outer edge of the A-ring? Well, I have a hard time believing it to be seen in any telescope much smaller than 10 inches. The diffraction effects would tend to make it blur into the darkening of the soft outer edge of the A-ring, making it invisible. As I have said before, as hard as the actual division has been to see in 10 and 14 inch apertures, I don't see it being visible in anything much smaller. Clear skies to you.




Yes that's what I meant in my last sentence. By "Encke" I meant the minimum, by "Keeler" what is now Encke in IAU nomenclature. I've never seen the latter myself. This was the nomenclature historically used before the IAU mess.

Ivano

Edited by idp (04/12/13 10:11 AM)


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azure1961p
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Re: Encke Division new [Re: idp]
      #5794209 - 04/12/13 11:24 AM

Nevertheless Im not hopeless on the matter!

Pete


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David Gray
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Re: Enckes new [Re: azure1961p]
      #5794333 - 04/12/13 12:18 PM Attachment (36 downloads)

Quote: David, what about Enke's division, ever seen it in your 16 incher

This is what I said in reply to Asbytec [not Ivano] on my "Saturn April 4" thread (Sketching Forum). [Edit Note: apologies for the original error]
.


If you mean the Encke Minima (what I call the ‘classical Encke’): yes on very many occasions. If the IAU Encke then on average some five or so times per apparition (edge-ons excepted!), but only during better seeing. This latter to me is the true Keeler Gap: the IAU compounding the silliness by calling an impossibly fine line even nearer Ring A’s outer edge the Keeler. Can I see the IAU Encke as a ‘black’ gap like Cassini? Definitely not. On the BAA intensity scale (0 = White/Bright; 10 = Black) I usually make it twixt 7 & 8. Appropriately it looks to me quite like a fine lead-pencil line tho’ often a little diffuse – especially on the inner edge. I can’t rule out contrast effects entirely, but in my view perhaps 60/40: and undecided which predominates: real or illusion!! Nature seems to like hiding real features, at least to some eyes, under illusion/contrast effects; Saturn’s rings seemingly being particularly prone.

Somewhere in the BAA Saturn archive is a drawing of the only time I saw IAU Encke in my 10” (1970s?) also in their Journal – will need to check.


Attached is a graphic to illustrate what I was trying to get across: I have digitally photo'd the 2003 drawing and rescaled vertically to nearer the Hubble image


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idp
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Re: Encke Division new [Re: azure1961p]
      #5796116 - 04/13/13 08:20 AM

Quote:

Oh tell me about it. I swear its tethered to my condo. Last good seeing for me was Thanksgiving week - a good 5 nights of it were 7/10. After that between 4-6/10.





There was a decent night last week, seeing maybe III but I observed Jupiter and then Saturn, both pretty low. I use the seeing forecasts from this website:

http://cleardarksky.com/c/YlStdObCTkey.html?1

It covers Connecticut pretty well, my hunch is that it used to be more accurate, but it's still useful.

Ivano


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idp
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Re: Encke Division new [Re: idp]
      #5796132 - 04/13/13 08:29 AM Attachment (31 downloads)

Just for the records, this is the best view I ever had of Saturn's rings with my old 8". Encke minimum's outer rim looked measurably darker, don't know if it had anything to do with Encke div. at all.

I can now routinely use a 10" Newton and a 10" refractor, but the position of the planet is not even remotely as good as it was back then for a northern observer.

Ivano


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azure1961p
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Re: Encke Division new [Re: idp]
      #5796174 - 04/13/13 09:05 AM

Huh. That's what I was referring to with my original post. The outer edge of the A ring appearing lighter indicating the outside ring seperated by Enckes or the Keeler Gap. Not that the gap was seen as such but the albedo difference between those rings being seen as drawn in your sketch. That was the query of my OP. That while the gap might be invisible differing contrast values between the ring sections still defines that outside ring edge.

Again, please Refer to Wes Higgins photo link above in an earlier post as he appears to have imaged what you drew. This seems less like he Envke Minima and more like that outside ring albedo.

Pete

Ps: here's the link again. I think you drew the ring as it is and not the minima.

http://www.cloudynights.com/photopost/showphoto.php?photo=348&password=&a...

Edited by azure1961p (04/13/13 09:08 AM)


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idp
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Re: Encke Division new [Re: azure1961p]
      #5796261 - 04/13/13 09:50 AM

Looks like Wes's processing was good for the globe but not for the rings (happens often). A and B rings' inner and outer edges much brightened, darker regions much darkened,
brightness steps turned into gaps.

I agree this looks like a darkening of Encke minimum's outer edge due to processing, rather than Encke's gap (OK I'll stop calling it Keeler). May have very well happened the same to me.

Ivano

Edited by idp (04/13/13 09:52 AM)


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azure1961p
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Re: Encke Division new [Re: idp]
      #5796289 - 04/13/13 10:04 AM

Well at anyrate your drawing answered the original query I had. I'm still between the minima and a ring albedo contrasts. Worth investigation anyway.

Great drawing too.

Pete


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Asbytec
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Re: Enckes new [Re: azure1961p]
      #5796737 - 04/13/13 02:44 PM

Yea, Pete, I remember that exciting night. After some research and some debate, I think ruling out the Enke osbservation was prudent. Working the numbers and the edge spread function, and thanks to input from David Knisely, I believe what I saw was not Enke minimum nor Enke. It was a brief seeing artifact that gave me that momentary boost of excitement. I see the Enke minimum regularly.

One the next balmy night, with boundary fan running, I'd be curious if you're planetary Newt could do it. Maybe.

Edited by Asbytec (04/13/13 02:50 PM)


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rgm40
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Re: Enckes new [Re: Asbytec]
      #5803528 - 04/16/13 09:03 PM

It is possible in a 8 inch. I got one, good, clear shot at it on one incredible morning of seeing. Never have I seen a better view of Saturn --and-- Jupiter on that same morning. I had a home built 8" f/6 with mirror supplied by Orion back in the 90's when Orion sold mirrors. I set up my scope in the back yard and went to bed. My alarm woke me up around 4:00 AM and I went outside. There was so much dew on my scope that the flocking paper separated from inside the tube and was hanging down. I was so frustrated that I almost packed it in without taking a look. After I calmed down, I decided to put in a U.O. 9mm VT Ortho and take a gander at the planets, hanging flocking paper and all. I could not believe my eyes. I had no idea the scope was capable of such views. I had never seen such color, cloud band detail, festoons, and such. And, I have not been able to duplicate it to date. I have often thought about trying it again sometime (letting the scope set out all night and getting up early--just before dawn) but have been afraid to let it set outside unattended. There is so much potential there for something bad to happen to it.

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buddyjesus
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Re: Enckes new [Re: rgm40]
      #5803672 - 04/16/13 10:46 PM

happy you made lemonade out of lemons rgm

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Ziggy943
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Re: Enckes new [Re: buddyjesus]
      #5803820 - 04/17/13 01:06 AM

I have seen Encke's exactly twice. Both observations were made from some of the better locations in Utah with the 9" Clark and in the company of confirming observers. The first observation was made at an elevation of 10,500 feet at Monte Cristo, the second at the Wedge Overlook. In both cases Encke was a fine line at the ansae of the A ring. It was not seen all the way around. It makes my my list of top 5 observations.

I almost had it in 2003 during an incredible morning in an TEC 8" F/15 MAK. Mars, the previous night had shown an incredible image at 19.6", the best ever in that scope that I had to try Saturn. It was sooo close and so good but not quite there. Seeing Encke depend on everything being just right.


Edited by Ziggy943 (04/17/13 01:13 AM)


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george golitzin
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Re: Enckes new [Re: Ziggy943]
      #5803950 - 04/17/13 05:17 AM

Quote:

... Seeing Encke depend on everything being just right.





I agree. I've seen it once, in a well-cooled 16-inch on a great night with the rings wide open and the planet very high in the sky (in Taurus, or perhaps Gemini--I'd have to check my notes...). One of my favorite observations ever. I was at 360X, which I think is near the minimum power necessary to pick out such a fine line.

-geo


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Peter Natscher
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Re: Enckes new [Re: David Gray]
      #5805682 - 04/17/13 10:18 PM Attachment (44 downloads)

I've seen the Encke Gap with my past 20" f/4.3 Zambuto Starmaster dob during the winter of 2006 when Saturn was in its northern-most apparition in the sky and the rings were open all the way. I was bino-viewing at about 500X with Saturn directly over head. The Gap was seen steadily as a fine black line with a contrasty appearance, not the gray, blurry and thicker line shown in the photos. It was a lot thinner appearing, but very black. See attached NASA image. The Gap appeared more like 'this' image -- very thin and black.




Quote:

Quote: David, what about Enke's division, ever seen it in your 16 incher

This is what I said in reply to Asbytec [not Ivano] on my "Saturn April 4" thread (Sketching Forum). [Edit Note: apologies for the original error]
.


If you mean the Encke Minima (what I call the ‘classical Encke’): yes on very many occasions. If the IAU Encke then on average some five or so times per apparition (edge-ons excepted!), but only during better seeing. This latter to me is the true Keeler Gap: the IAU compounding the silliness by calling an impossibly fine line even nearer Ring A’s outer edge the Keeler. Can I see the IAU Encke as a ‘black’ gap like Cassini? Definitely not. On the BAA intensity scale (0 = White/Bright; 10 = Black) I usually make it twixt 7 & 8. Appropriately it looks to me quite like a fine lead-pencil line tho’ often a little diffuse – especially on the inner edge. I can’t rule out contrast effects entirely, but in my view perhaps 60/40: and undecided which predominates: real or illusion!! Nature seems to like hiding real features, at least to some eyes, under illusion/contrast effects; Saturn’s rings seemingly being particularly prone.

Somewhere in the BAA Saturn archive is a drawing of the only time I saw IAU Encke in my 10” (1970s?) also in their Journal – will need to check.


Attached is a graphic to illustrate what I was trying to get across: I have digitally photo'd the 2003 drawing and rescaled vertically to nearer the Hubble image




Edited by Peter Natscher (04/17/13 10:23 PM)


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azure1961p
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Re: Enckes new [Re: Peter Natscher]
      #5805758 - 04/17/13 10:43 PM

Amazing how light the hex is in that image. Ok back on topic...

Pete


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buddyjesus
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Re: Enckes new [Re: azure1961p]
      #5805895 - 04/17/13 11:43 PM

beautiful picture!

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John Boudreau
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Re: Enckes new [Re: azure1961p]
      #5806227 - 04/18/13 08:20 AM

Quote:

Amazing how light the hex is in that image. Ok back on topic...




That image shows the south polar region--- Only the north polar region has a hexagon feature. That image was probably taken about 10 years ago. The north polar hex does show in HST images taken in the early 90's though.


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David Gray
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Re: Enckes new [Re: Peter Natscher]
      #5806294 - 04/18/13 09:06 AM

Quote:

I've seen the Encke Gap with my past 20" f/4.3 Zambuto Starmaster dob during the winter of 2006 when Saturn was in its northern-most apparition in the sky and the rings were open all the way. I was bino-viewing at about 500X with Saturn directly over head. The Gap was seen steadily as a fine black line with a contrasty appearance, not the gray, blurry and thicker line shown in the photos. It was a lot thinner appearing, but very black. See attached NASA image. The Gap appeared more like 'this' image -- very thin and black.




It used to be said that 20" was about the aperture to get Encke as a true black gap.

Looking back through my old observations the darkest I got it, in excellent conditions, was intensity 9 which roughly equates to 90% black but still a little diffuse - so perhaps my 415mm D-K is on the edge!


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azure1961p
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Re: Enckes new [Re: David Gray]
      #5807778 - 04/18/13 09:42 PM

John,

Thanks for the clarification. I didn't realize it was pole specific. How odd.

Pete


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Mark Harry
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Re: Enckes new [Re: azure1961p]
      #5813821 - 04/21/13 06:48 PM

Once for Encke, and once for 8 Trap stars 3 years ago- Both times with 8" F/6, and the UO VT 9mm Ortho. Fantastic eyepiece. Conditions have to be essentially perfect; the least disturbance makes them disappear.
M.


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Asbytec
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Re: Enckes new [Re: Mark Harry]
      #5814334 - 04/21/13 10:38 PM

8 Trap stars in an 8"...wow, well done.

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azure1961p
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Re: Enckes new [Re: Asbytec]
      #5814371 - 04/21/13 11:02 PM

8 Trap stars????????

Ok there goes a gauntlet!

Pete

Ps: I agree on the UO volcano top 9mm - an excellent ocular.

Edited by azure1961p (04/21/13 11:03 PM)


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David Knisely
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Re: Enckes new [Re: Mark Harry]
      #5814566 - 04/22/13 02:11 AM

Quote:

Once for Encke, and once for 8 Trap stars 3 years ago- Both times with 8" F/6, and the UO VT 9mm Ortho. Fantastic eyepiece. Conditions have to be essentially perfect; the least disturbance makes them disappear.
M.




The Encke "minimum" in a 8 inch I would believe (especially at lower powers). However, seeing the actual 325 km width division in that aperture is problematic at best due to diffraction effects between the division and the darkness at the edge of the A-ring. Even under the best conditions, the division is just too close to the darkness at the outer edge of the A-ring (0.496 arc seconds from the edge at mean opposition). For this reason, I may have some doubts about claims for visibility of the gap itself in only an eight inch aperture, although I won't dismiss them entirely. Clear skies to you.


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Mark Harry
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Re: Enckes new [Re: David Knisely]
      #5814686 - 04/22/13 06:48 AM

Read EDZ's discussion on the link.(?)
***
Oh well, folks have been telling me I can't see squat for decades anyhow. Up to 2 years ago, I had 20/10, and almost reached senior citizen status with it. I feel fortunate. May your skies be clear as well.
M.


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Mark Harry
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Re: Enckes new [Re: Mark Harry]
      #5819936 - 04/24/13 02:36 PM

No offense meant; almost as if this thread has shut down. Lets just say, I'm trying to grow old as gracefully as possible!!!
M.


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azure1961p
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Re: Enckes new [Re: Mark Harry]
      #5819961 - 04/24/13 02:45 PM

Mark,

I don't think any offense was taken. Its merely the momentum or lack there of in the topic. Without having seen it myself I don't think its impossible merely exceptional to rare.

Pete


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Schaden
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Re: Enckes new [Re: azure1961p]
      #5832120 - 04/30/13 12:09 PM

I saw Enckes in my Nexstar 8 last weekend. The seeing in Phoenix was phenomenal. Cleardarksky predicted 4/5 in the early evening and 5/5 after 1am for transparency and seeing. I was using an 11mm es82 barlowed to 360 x.

I've never seen it look so good at that high of power. It revealed more detail than 180. Don't know the name, but I saw the crisp shadow of a large lunar crater. Inside I could see the smooth wall that looked like a giant sand climb challenge and an endless array of tiny craters everywhere, they emerged into view with the higher mag, the seeing was superb. I used one extremely tiny one to focus on, the inside walls only visible momentarily.

When I saw Saturn it immediately looked better than it's ever looked in the C8 or Z10 before or since. The planet's bands were vibrant. The rings were tack sharp. I could see shades of contrast within each ring. I could see the rest of the A ring around Enckes, the gap appeared as a thin black line out on the edge of the A ring, flickering in and out in clarity from minute to minute but no doubt visible with direct vision.

That taught me seeing is the single most important variable in planetary observing. I got an amazing view from a light polluted city with a nearly full moon.


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Re: Enckes new [Re: Schaden]
      #5832666 - 04/30/13 04:07 PM

Despite excellent seeing, I have never seen the Encke division in my Nexstar 9.25GPS XLT at any power. Seeing has sometimes caused a "doubling" of the outer edge of the A-ring that mimics a division there (especially if I have any tube currents in the scope or I have not used my Cat Cooler enough). However, once seeing settles down, the effect vanishes. I often use the visibility of Enceladus to check on seeing, as if it isn't rock stable, that faint little moon is often not seen in the 9.25. Indeed, my sighting of Enceladus so easly in the 9.25 when I was reviewing the scope for my Cloudynights review of it was one thing that convinced me that the scope was of excellent optical quality (and I eventually ended up buying the instrument). Clear skies to you.

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Schaden
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Re: Enckes new [Re: David Knisely]
      #5833466 - 04/30/13 11:36 PM

I didn't see it until my scope had been outside for 2 hours. There is no doubt in my mind it was Enckes, it wasn't a mirage of Cassini. I think you just need perfect seeing. That was the best night I've had in the last 4-5 years and approximately 100 sessions. I regret not staying up later but I was dead tired at 2am. The website had predicted 5/5 seeing again the next night but when I checked again the next afternoon it was only predicting an average 3/5 night. So I feel lucky to have had the hour of perfect seeing. It really was an exceptional night, knowing what my scope is capable of doing given the conditions is a good thing, but it's depressing to think of going out on an average night now, given how much I know is missing.

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azure1961p
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Re: Enckes new [Re: Schaden]
      #5833726 - 05/01/13 06:41 AM

I agree that when truly pristine seeing comes in its a revelation and you finally get to see all the precision in your optics at work - its awe inspiring! Too, as you mention, it is a but of a let down when you realize what you've been missing!!! Thanks for your account here. It sounds like your cass is a keeper.

Pete


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Re: Enckes new [Re: azure1961p]
      #5836745 - 05/02/13 05:00 PM

With discussion with one of the participants. it kind of "P"d me off; with the condescending attitude of the questioner brought to the table.
******
I have been labeled as having 20/20 vision by a highly regarded optometrist;.
The discussion with the questionable respondent, commented the impossibility of seeing the small division; in MOA of the object in question. I never got a response in what the rez his particular eyeball was capable of. It didn't confirm what I know of optical theory, etc.
This got my 'interest' so I decided to make a SWAG.
While "blessed" with 20/20, I noticed I could discern (this last weekend; repeatedly and confirmed by another observer) a 1/4-5/16th" -LINEAR- defect at approx 175 yards, which would equate to ~ .17 MOA @ 100 yards: ~ which equals the rez @ 100 yards.
This is what a supposed individual with 20/20 vision could discern at that yardage.
FWIW, the width of angle @ 175 yds equates to .143 MOA at 100 yards. This partalleled exactly what ED Z quoted in his discussion a few years ago in a reference thread.
The individual has failed to reply to repeated queries about detecting this resolution. He also publicly doubted what I could have seen with an 8" aperture.
His insistance, I could not detect anything smaller than 2-3 MOA........Really???
-----------
Now, I wonder who's word that would appear as being acceptable???????
Don't ask for the name of the condescender. I will not give it. But this brings up another point.
********
"excellence is the enemy of the 'good'."

I know what I saw.
My only fault; I did not record the observation of Encke. I don't have the specific dates. But I do recall it was visible in my scope; and it wasn't in a particular Russian Mak.
(SCT's- don't even apply.)
M.


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Re: Enckes new [Re: Mark Harry]
      #5836987 - 05/02/13 06:50 PM

Hi Mark,

Thanks for your input here . Its a discussion after all so it will have views or opinions on both sides of the fence and some like me sitting in the middle (ouch). I appreciate your accounts here and weigh the other remarks by valid observers as testament to the exceedingly difficult nature of this feature. I'm not slathering it on - I have belief or faith it can be seen with an 8" though I've failed - in great seeing- and with s great system. Your scope sounds like its top wrung and your observations were careful.
I found your contribution enlightening and well explained.

I am impressed with your naturally good vision, I wear contacts. However since the scope focuses past the effects of near or far sidedness, I'm not sure its a defining attribute, like , no astigmatism would be.

Again thank you for your contribution to the thread.

Pete


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Re: Enckes new [Re: Mark Harry]
      #5837605 - 05/03/13 02:46 AM

Mark Harry posted:

Quote:

While "blessed" with 20/20, I noticed I could discern (this last weekend; repeatedly and confirmed by another observer) a 1/4-5/16th" -LINEAR- defect at approx 175 yards, which would equate to ~ .17 MOA @ 100 yards: ~ which equals the rez @ 100 yards.




OK, a single dark line against a light background that was 1/4" across at a distance of 175 yards would subtend an angular diameter of about 8.2 arc seconds. Detecting that line at that distance with the unaided eye would be a fairly decent feat but definitely not even close to being the best that is possible for a good set of eyes. Indeed, Sidgwick (Amateur Astronomer's Handbook, 2nd edition, p. 430-431) mentions observers with good eyesight seeing a longer linear feature like that down to an angular width of around an arc second or so. In fact, a few observers with great eyesight have gone as small as a width of only 0.44 arc seconds (Barnard, using a wire against the daytime sky).

In telescopes, thin linear features have been detected having widths much smaller than standard resolution figures such as Dawes Limit or the Rayleigh criterion. This can be shown by the fact that Cassini's Division was discovered in a telescope (2.5 inches of aperture) that does not have enough resolution to resolve the angular width of the division. Indeed, in that same book (Sidgwick, p. 50), it is noted that detection tests managed to show a linear feature that had an angular width of as fine as 1/14th to 1/15th that of the usual Dawes figure for that aperture.

Encke's division has a physical width of 325 km, which at mean opposition distance, would mean an angular width of about 0.052 arc seconds. This would mean that considering the division as a linear feature and using 1/14th of the Dawes Limit for an 8 inch (0.041 arc seconds), *if* the division was in the middle of a white background with absolutely nothing anywhere near it, it should at least have the potential of being detected in an eight inch aperture.

However (you knew that was coming, right? ), the problem is that the division is *not* isolated. It sits on a light grey background only around 0.5 arc seconds from the massive darkness at the edge of the A-ring. This dark edge would act as a second (and much higher contrast) linear feature sitting right next to the division. In that case, one would have to consider the resolution limit of *two* linear features and not just the detection of an isolated feature. For that, we can again refer to the experiments quoted by Sidgwick. Treating the division and the outer edge of the A-ring as "parallel lines" is somewhat more realistic here than just using one of the standard resolution criteria or a mere detection criteria. To quote Sidgwick (from AMATEUR ASTRONOMER'S HANDBOOK, 3rd edition c. 1980, Dover, Section 2 (Telescopic Function: Resolution), p. 50) where R' is Dawes Limit (4.56/D):

Quote:

"C. PARALLEL LINES ON A LIGHT GROUND

(i) W. H. Pickering: minimum separation for resolution with a 10-in reflector was 0".63 (1.4R'),

(ii) A similar performance was given by the Arequipa 15-in, which resolved a pair of parallel lines when their separation was increased past 0".42 (1.4R', in good seeing. Slight atmospheric deterioration immediately raised the threshold to about 2R'. At less than 0".42 the lines appeared as a grey band of width about 1-1/2 times their separation.

(iii) Resolution of the lines at 12" arc with 0.4 in OG (1.1R'). See also sections 2.3, 24.6, 26.7, 26.9"




Having too small an aperture resulted in the two lines merging into a diffuse band rather than being resolved as two clearly separate features. Using the most "liberal" (iii) limit of 1.1R' and the 0.5 arc second mean separation between the Encke division and the edge of the A-ring, the aperture required for such a resolution of parallel lines would be about 10 inches. Using apertures much smaller than this would result in the Encke division being basically "swallowed-up" by the diffraction effects caused by the presence of the darkness of space at outer edge of the A-ring. This is the main reason I may be somewhat dubious about the prospect of seeing the Encke division in apertures much smaller than around 10 inches, although as I clearly stated before (and in a proper and civil manner), I won't exactly rule it out. Clear skies to you.


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Re: Enckes new [Re: David Knisely]
      #5837846 - 05/03/13 09:01 AM

This makes an interesting bone to worry.
****
Still curious, I took a scope that was apertured to 50mm, and of F/12-600mm focal length. In it, was a 42mm eyepiece for a mag of 14.3x. A refractor might not be the best type to use, but it was handy; regardless that it (achromat) will only focus perhaps green the best and the other 2 main colors would smear with any substantial magnification.
In my PMs, I mentioned I could see 1/4" spaces between white painted planks at 100 yards. One of the spaces is actually 1/8th inch. so I think that's pretty good.
1/8 MOA =7.5 arc seconds. Eye pupil was around 3mm; 1/8".
There are also 1" dots at that range, and they are plainly visible. A smattering of .22 bulletholes are for all intents, invisible by eyeball.
The refractor brought all the holes out plainly.
There are surface checks on the surface, and ends of the planks. .010" ones are easy to see, and .005" are regularly seen with little trouble. Even the glint off a spiderweb was visible at the same distance, but I have no idea of it's actual width. Suffice to say, I think it's realistic to estimate it as half a thousanth (.0005", but likely significantly smaller than that!) I will use .0005". This latter item figures to .03 arc seconds. Hmmm- with a 50mm aperture.
Well let's see what that would be with a 200mm aperture.(~8"):
.03 x 50/200 =.0075 arc second.
***
Now, if Encke is .052 arc second.......
If atmosphere cooperates, there should be no problem seeing Encke with 8": -IF- the .052 arc-second figure is correct.
******
It was 38 degrees this morning; right at sunrise. The refractor was working very well. The sun started to show on the ground a distance in front of this plank wall; at a very acute angle. Seeing deteriorated almost immediately. The .005-.010" surface checks took on a fuzzy characteristic.
And I think the most important thing; I didn't have to read a thing, or dig up any kind of source material. Just go out, do a little looking, measuring, and get the real deal.
Another aspect, is the discrepancy found in looking for essentially point sources, vs linear ones. Quite a difference. If I was to hazard a guess, a 1/2" dot at this 100 yard distance would be quite taxing by eyeball alone.
****
One can only surmise that a smooth accurate reflector with zero color can have the magnification raised without the degradation that goes along with a simple achromat. I used only the combination I outlined above, along with a 2" erecting diagonal to give the refractor a chance to show as little color error as possible. The Newt I had suffered from none of these issues. With a bit more "colorless" power applied, I imagine linear features could be detected 2-4x smaller.
Well, that's about all for my little experiment.(or rant, which depends on just what side of the fence you're on.)
Regards,
M.
PS: might be interesting to hear what other folks might find out-


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Re: Enckes new [Re: Mark Harry]
      #5838451 - 05/03/13 02:00 PM

Mark Harry wrote:

Quote:

If atmosphere cooperates, there should be no problem seeing Encke with 8": -IF- the .052 arc-second figure is correct.




That 0.052 arc second figure for the angular width of the Encke Gap is indeed quite correct for a mean opposition distance of Saturn (1277.42 million kilometers). You take the physical width of the Encke gap (325 km) and divide it by the opposition distance to Saturn. Then, you take the inverse tangent and convert the result into arc seconds. Again, however, you seem to be continuing to miss the point that the division is *not* sitting all by itself. The division has a diffraction structure at apertures too small to resolve it, with a central maximum darkness at its precise geometric center and a gradually reducing darkness the farther away from the center that you look. Diffraction basically "softens" the division from a hard thin line to a soft broadened band. That kind of diffraction structure is also present on the edges of the A-ring. These two diffraction structures will interact if they are close enough together. As I clearly explained earlier (both in PM and here), the telescope must have sufficient resolving capability to clearly separate the division from the edge of the A-ring. Eight inches is just a little on the small side for this to occur. This has nothing to do with visual acuity, but concerns the physics of light. Clear skies to you.


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Re: Enckes new [Re: David Knisely]
      #5838782 - 05/03/13 05:25 PM

And -YOU- are -NOT describing the true situation presented, either. (now, or before) It's not just 2 simple parallel lines.
Quote all you want, and argue until blue in the face. I know what I saw, and have an idea how to determine seeing conditions, quality of optics, what can be seen, etc.
Good day to you,
Mark


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Re: Enckes new [Re: rgm40]
      #5838784 - 05/03/13 05:26 PM

Just got it today for the first time in my 8" SCT at 30-37 degree elevation and rather good seeing, at 330x and 440x.

P.S.: I'm talking about Encke's minimum.


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Re: Enckes new [Re: leviathan]
      #5839496 - 05/04/13 02:46 AM Attachment (16 downloads)

At least you got to see it (the planet and the minimum). I just wish the weather would cooperate for once. It has been cloudy, cool, and rainy for weeks (even had snow day before yesterday). The last time I was preparing to get the scope out for Saturn a few nights back, by the time I got things ready and went back outside to get the first piece of equipment out, the sky had completely clouded over. The forecast looks like it will be Monday at the earliest before I can get another look at that planet. Sheesh, what a spring! Kind of makes you wish you were getting the view the starship below is getting. Clear skies to you.

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Re: Enckes new [Re: David Knisely]
      #5840759 - 05/04/13 09:18 PM

What I saw in the A ring looked like that picture posted by Peter Natscher. Enckes appeared as a black line, very similar to the way Cassini usually looks but thinner and fainter. The A ring looked the same on each side of it. Although the A ring did change as it approached Cassinis. And the B ring had a lighter and darker section within it too. Prior to that night, I had only been able to notice a simpler contrast between the different single shades within each the A and B. The cloud bands stood out too. They seemed more vibrant than usual, each had a distinct color instead of the normal very subtle differences between them.

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Re: Enckes new [Re: Schaden]
      #5841020 - 05/05/13 01:02 AM

I observed Enckes on two occasions in the Summer of 2001 using my superb orange tube C8. Outstanding seeing (rare). Using a UO 5mm Ortho. I've never seen it since. A view forever burnt in my memory.

Charles


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Re: Enckes new [Re: David Knisely]
      #5846118 - 05/07/13 05:22 PM

In experiments done with a variable aperture mask on the Cassini division, it was determined that while a 50mm (2 inch) aperture would allow marginal "detection" of the Cassini division, it took a 2.4 inch (60mm) aperture to show it more firmly around the ends of the ring ansae (and the division itself was discovered in a 2.5 inch aperture). At apertures smaller than 50mm, the division basically bended into the darkness of the outer A-ring and was not visible other than as the generally darkening of the ring itself. This shows the same sort of effect that would make the actual Encke Gap vanish if too small an aperture was used. The Cassini Division's center separation from the outer edge of the A-ring is roughly 16,950 km, so at a mean opposition distance of 1277.42 million km, that distance would subtend an angle of about 2.74 arc seconds. This is around 1.2 times the Dawes resolution figure for a two inch aperture, which confirms the idea of considering the division and the edge of the A ring as two parallel lines. Extending this again to the Encke gap, it lends observational support to the estimate that it would probably take something on the order of a ten inch aperture to have much of a chance of separating the gap from the darkness of the outer edge of the A-ring. Clear skies to you.

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Re: Enckes new [Re: David Knisely]
      #5846318 - 05/07/13 06:39 PM

Quote:

Kind of makes you wish you were getting the view the starship below is getting.





That's the kind of view I had one magical, slightly-overcast night with my 14" SCT and a 7mm Nagler T1 (~508x). Just like I was in orbit!
It's never happened again, but that was enough to reassure me that it's possible, and can come again!

*sigh*


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azure1961p
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Re: Enckes new [Re: Rick Woods]
      #5846747 - 05/07/13 10:12 PM

That had to be very impressive Rick and the good news is odds are you'll have it again.

Pete


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Re: Enckes new [Re: Rick Woods]
      #5846833 - 05/07/13 10:51 PM

I had one of those nights with my binoviewer. In the 14 inch, it was like looking at 3-D model of the planet based on an HST image, but sadly, those nights tend to be few and far between. Clear skies to you.

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Re: Enckes new [Re: David Knisely]
      #5847246 - 05/08/13 07:31 AM

Quote:

In experiments done with a variable aperture mask on the Cassini division, it was determined that while a 50mm (2 inch) aperture would allow marginal "detection" of the Cassini division, it took a 2.4 inch (60mm) aperture to show it more firmly around the ends of the ring ansae (and the division itself was discovered in a 2.5 inch aperture). At apertures smaller than 50mm, the division basically bended into the darkness of the outer A-ring and was not visible other than as the generally darkening of the ring itself. This shows the same sort of effect that would make the actual Encke Gap vanish if too small an aperture was used. The Cassini Division's center separation from the outer edge of the A-ring is roughly 16,950 km, so at a mean opposition distance of 1277.42 million km, that distance would subtend an angle of about 2.74 arc seconds. This is around 1.2 times the Dawes resolution figure for a two inch aperture,
***
which confirms the idea of considering the division and the edge of the A ring as two parallel lines.

*** Extending this again to the Encke gap, it lends observational support to the estimate that it would probably take something on the order of a ten inch aperture to have much of a chance of separating the gap from the darkness of the outer edge of the A-ring. Clear skies to you.




-------
No, it does not. That is -NOT- the situation. I also know that you did not personally make this assessment; for I read it years ago as well.
***
I have a good friend the other side of town. You once made a remark about visual acuity not mattering; only the physics of light.
This guy was born legally blind. He can 'SEE' but at a much reduced level of acuity. He's not resentful of the fact, but accepts it as the hand of cards he was dealt. One of the finest mechanics I've ever known.
But I'm sure he could relate how this handicap has affected his whole life; and how he's had to make accomodations for it.
Think how it would be to never be able to posess a driver's license???
He's never said anything, but I know he would like to be able to drive; and not be reliant on someone else doing it for him.
He would be quite contented with a 1/2-1 wave error scope of any type, -IF- he could use typical eyepiece formats in use today (1.25 & 2")
--------
Back last page, I related and described a duplicateable "test". In simplest terms, I have described basic rez of the aperture in question--- It's first hand, and I have strived to make it the least subjective as possible; and understandable by anyone.
Your replies and arguements have no personal observations or information derived as close to original source as this. All they contain, is second- or third- hand knowledge; and some of this, I question the validity of such. It's anecdotal, to say the least.
****
There -HAS- to be a reason for the existance of custom optics makers the likes of Zambuto, Stevens, Dodds, Cowan, etc. A look thru the eyepiece generally is all the proof needed. The claim you have stated where there are no returns after 1/10th wave optics, is just where most of these aforementioned guys are getting down to serious figuring. People can see the difference, and are willing to pay big bucks for it.
There was recently a claim of viewing Saturn in another thread, where 200 and 400x were used. It was remarked how @ 200x, it was sharp and clear, whereas @ 400x the view was softer, and not so crisp. This brings up another point you have objected to, but others (and what I mentioned before here) have noted. Mags can work against high resolution views. Good accurate optics will provide better views at lower powers; not just high ones. Being fully saturated with light allows those who have the acuity to pick up ever-so-slight details that other less capable individuals will miss at higher powers. I believe that's the case here; for you remarked about ~400x being used and failing to see the hairline detail in question with your 9.25" (?)
I appologize for the straying somewhat from the OP, but this may be of help in successful planetary observation; and to dispell misinformation. I don't think my observation last page should be discounted just because my last name isn't Sidgewick. (sp?)


Edited by Mark Harry (05/08/13 07:35 AM)


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azure1961p
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Re: Enckes new [Re: Mark Harry]
      #5847254 - 05/08/13 07:41 AM

Mark,

I appreciate your points on these matters though in the case if the mechanic it would seem his vision is so extremely bad it doesn't apply to a simple matter of nearsighted or farsighted with the focusing of the telescope essentially doing it for the cornea wether its up to it or not. If there's retina issues, astigmatism, horrendous floater obstructions - then that's another story. At anyrated Im quite nearsighted but I can focus everything I own to unerring sharpness - tho the large exit pupil in the binos begins to reveal astig as well as my 26mm plossl.

Thanks.

Pete


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Re: Encke Division new [Re: BillFerris]
      #5848056 - 05/08/13 03:47 PM

This discussion illustrates well some of the challenges one encounters when attempting, making and reporting a threshold visual observation. Visual observing is a wholly subjective activity. Regardless of the degree to which one intends or attempts to be objective, the act of making a visual observation is ultimately inseparable from the subjective interpretations made by the observer. In many cases, this is not an issue. The handful of Saturn observations published to my Website, Saturn, are generally non-controversial. The physical details captured in my drawings are known to exist and are commonly reported by other amateur astronomers and astroimagers. As such, they don't merit scrutiny. Even if I was mistaken about observing a reported detail, an experienced observer would acknowledge that many reliable observations of that detail exist. My potential error wouldn't create an unreasonable expectation of what can or cannot be seen.

Visual observing gets more complicated as the objects and details reported lie closer to the threshold of what is considered possible given the equipment being used and the conditions under which the observation is being made. An observation of an object or detail at the threshold of visibility is, by its very nature, of questionable reliability. The observation is considered to be highly difficult and, perhaps, even of questionable possibility. If I were to report a naked eye observation of a 10th magnitude star, that report could--I would say, should--be received with substantial skepticism. Our contemporary understanding of the limits of human visual acuity do not allow the possibility of a person seeing a star that faint. The historical record does not include reliable reports by observers claiming to see a star that faint. No living amateur astronomer has ever personally seen a star fainter than, perhaps, mid-8th magnitude without optical aid. A very natural and understandable response to the claim might be, "If I can't do it, and nobody else has reported doing it and medical science doesn't support the theoretical possibility of someone doing it...why should I believe you did it?"

Therein lies the crux of the issue, "Why should I believe?" As astronomy enthusiasts, most of us value logic and objective evidence as the arbiters of what is and is not to be believed. There is no physical sensation of being on a planet rotating about its axis at 1,000 miles per hour. But the objective evidence indisputably supports the statement that Earth does, in fact, rotate at that velocity. The objective data gathered by professional and amateur astronomers, alike, are daily reminders that phenomena like novae, comets and planets orbiting other stars do exist. These are unquestionable facts of nature. And the data collected in a rigorous manner can be used to confirm or refute our theoretical understanding of the how or why such phenomena occur.

Visual observations at the threshold are much less tidy. In a civil forum such as this, we can all agree to accept that all participants in a discussion are forthright, honest folk. Whether or not we believe what someone has claimed to have done, we can at least accept that the person genuinely believes they have done it. They believe they've successfully made a threshold observation. Beyond that, it is difficult to say much more with any degree of certainty.

With regards to the current thread, we should all be in agreement that visual detection of the Encke Division is a difficult observation in any amateur telescope. Unlike the Cassini Division, the Encke Division is not an obvious feature. This razor thin division just inside the outer edge of Saturn's A-Ring was observed by James Keeler in 1888 using the Lick 36-inch refractor. It has since been observed in smaller apertures but--there's always a 'but'--reliable visual sightings in small to moderate aperture are uncommon. If an observation of this delicate feature is difficult in a quality 24-inch aperture, an reported observation with an 8-inch aperture certainly qualifies as a threshold detection.

Now, I'm not going to take a position for or against the report. What I will do, is suggest that folks keep a couple of items in mind. One, the person reporting the observation honestly believes he observed the Encke Division. He's openly given details about the telescope used, the conditions and what he believes he saw. No one should question the integrity of the report and certainly not of the person. Two, it's a threshold observation. As such, many observers attempting to repeat the observation will--even if it is possible--fail. As such, there is room to doubt the accuracy of the person's honest interpretation of what they saw. This is the nature of threshold observations: there is room for doubt.

If this were an annual conference and I was presenting peer-reviewed research and a new theoretical model for some natural phenomenon, it would be fully appropriate for my professional colleagues to hammer me with questions probing for errors in my procedure, analysis or conclusions. But that is not this forum. This is a public forum of astronomy enthusiasts. And despite the misgivings those of you who are ardently anti-Facebook will have, I would argue this forum is not much different from any other social media site on the Web. As such, I would suggest that when it comes to reported threshold observations, it is reasonable and appropriate to point out the difficult or challenging nature of such an observation. But it's probably best not to push a questioning or doubting response too far. At some point, we should acknowledge that a person is honestly reporting what he believes he saw...an object or detail at the threshold of visibility which others may or may not have success in seeing for themselves.

Bill in Flag


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Re: Enckes new [Re: Mark Harry]
      #5848219 - 05/08/13 05:03 PM

Mark, I'm sorry, but this may be getting a little personal. As you have blocked me from responding to you privately, I would suggest that you unblock me if you wish to continue to respond to me rather than posting it here. I never said that you didn't see anything in your 8 inch. In my personal communication to you, I stated that, "I don't know what you saw, but I don't doubt your honesty. Your observation is interesting, but I can't know exactly what you saw as I wasn't there. I stated on this forum early in this thread; "I may have some doubts about claims for visibility of the gap itself in only an eight inch aperture, although I won't dismiss them entirely". I won't rule out an 8 inch for this, but I for various reasons, I think a slightly larger aperture may be required. I gave the perfectly valid reasons why I feel this way and backed that up with scientific reasoning and evidence, but you summarily dismissed them. Seeing as how you have blocked me, I will have to respond to you here, although as I have stated, this would be better off-forum.

Mark Harry wrote:

Quote:

No, it does not. That is -NOT- the situation. I also know that you did not personally make this assessment; for I read it years ago as well.




You are, unfortunately, quite wrong here when it comes to my assessment of the visibility of the Cassini Division. You may indeed have read something about this years ago, but you definitely do NOT have facts about this story. The experiment on the visibility of the Cassini Division was performed by *me* in 1999 and 2000 using my 10 inch f/5.6 Newtonian and my variable aperture stop. I put out the entire results of my experiment a number of times in the early 2000's in an article posted on the Usenet newsgroup sci.astro.amateur, as well as here on Cloudynights. A small portion of its results was excerpted from my original posting and later formally published in an article on observing Saturn's rings in Sky and Telescope magazine. Surprisingly, I have been published a few times in that magazine (and in Sky Publishing's older Night Sky magazine which is no longer in print). You can go back through the Sky and Tel archives to see the original article if you like (and the original Usenet posting may still be out there somewhere), but the fact remains that I did the work. I can provide the portion of the article concerning the experiment here:

"...At smaller apertures, the division would tend to just blend into the darker color of the A-ring, rather than forming a distinct dark gap. The division exists of course, but at what point does it become visible as a curving arc, and not just as a contrast effect?

To answer this, I used my off-axis variable aperture mask I built for my ten inch f/5.6 Newtonian to judge double star resolution. This mask provides me with 94mm, 80mm, 70mm, 60mm, and 50mm clear apertures, and I put on one additional mask to get 40mm and 30mm apertures. This way, I could stop down the scope in well-defined steps to see at which point the division would become invisible. I primarily used 176x and 141x for my tests, although I did try 235x and 101x as well. I did the tests in October in both 1999 and 2000 on nights when seeing was better than one arc second. I started with the widest opening 94mm (3.7 inches), which, at 141x and 176x, showed Saturn nicely and the Cassini Division much of the way around the planet. Even the main belt across the planet was easily visible, as well as the faint Crepe ring. Stopping down caused a drop in the brightness and in the ease of detail visibility, but Cassini's Division could still be seen down to 60mm, where it was still fairly traceable along a wide arc of each ansa. At 50mm, the actual division was becoming more difficult and was not very well shown, detectable mainly at the bend of each ansa. The outer half of the ring system looked somewhat darker as the division started to blend in a bit with the A-ring. At 101x, the division was not visible at 50mm aperture. At 40mm, I could no longer see a clear dark division between the rings, although the A and B-rings could still be seen as separate features with differing brightness and borders. Interestingly enough, even the 40mm aperture was still showing the main belt on the planet's disk. At 30mm of aperture, the A and B rings began to merge somewhat, with no clear signs of any division, and the only visible ring detail being a somewhat darker outer edge. I tried the same variable aperture sequence at 235x, but again, at 40mm, Cassini's division was not visible. To be realistic, while 50mm may allow "detection" of the division at high ring tilt, in general, 60mm seems to be about the minimum to clearly and easily show Cassini's Division.
..."

The results of the Cassini division experiment do tend to lend at least some support to the idea that a division and the darkness at the edge of the A-ring can be represented as parallel lines and may require a little more than the Dawes resolution limit to be seen as separate features and not just a diffuse band. By analogy, that representation may also be applied to the Encke Gap. By extension, it also suggests that it could take something close to 10 inches to also separate the Encke gap from the darkness at the edge of the A-ring as well. As I mentioned, I have not seen the Encke Gap in my home-built 8 inch f/7 Newtonian or in my NexStar 9.25 inch SCT, but I have (barely) detected it in my 10 inch Newtonian. Indeed, a friend of mine remarked about it last night when he recalled seeing it in my 10 as well. He has a custom mirrored 8 inch Newtonian as well (Enterprise Optics) that tests out as excellent (about 1/18.9th wave p-v wavefront, Strehl 0.994), so while he has yet to see the Encke Gap in his scope, he is still wanting to try again. I may have a few doubts that he will succeed, but he has excellent vision and equipment, so he will be trying again.

Quote:

Your replies and arguements have no personal observations or information derived as close to original source as this. All they contain, is second- or third- hand knowledge; and some of this, I question the validity of such. It's anecdotal, to say the least.




I'm sorry, but as I have demonstrated, you are incorrect. The information is not "third" hand. It is from the formal studies summarized and published in book form (along with my own experimental study on the Cassini Division). I provided full references here, so there is nothing "anecdotal" about it. Your statements are beginning to get maybe a little personal here, so again, this should be taken off-forum.

Quote:

The claim you have stated where there are no returns after 1/10th wave optics,




This again is off-topic. I stated to you that there are not any huge returns, not that there are *no* returns. You gain some contrast with a very smooth mirror (which anything significantly better than 1/10th wave p-v often tends to be) but it is not exactly an enormous image quality boost. I know the gains that can be had by going to something finer than 1/10th wave (I have two mirrors of that superb quality), but especially for large mirrors, other factors (seeing, thermal issues, optical support issues, tube currents, etc.) tend to negate at least some of that gain. In any case, you are again bringing things (like visual acuity) that are best handled off-forum. We are supposed to be talking about the Encke features (minimum and gap) here and not other things which may not have much bearing on the subject of this thread.



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Re: Enckes new [Re: David Knisely]
      #5849438 - 05/09/13 08:24 AM

Bill has outlined -PRECISELY- my whole point. (appreciated, btw)
I see a thinly veiled attempt to discredit my observational abilities at every opportunity. Your last post is quite obvious in the intent. Not only do you attempt to claim fame at someone else's expense, but I can see you have basically drastically reduced the credibility of your arguements. I knew you wrote that article, but I wanted to see if you'd 'rub it in'; which you've done. Thanks for giving me the true character insight; much appreciated, Dave.
****
But I think everyone has missed my point about visual acuity.
****
"Whitey" would be satisfied with a 1/2-1 wave instrument. He's albino. There is quite a larger issue than being just near/far sighted. I'm sure he would think this the best thing since sliced bread.
Dave's limit is what he has stated as 1/10th wave. this is where his acuity must "run out" and has himself claimed there is no/-LITTLE- improvement with any accuracy better than that.
I know several individuals who insist (myself included) that there's a noteable difference with optical trains with smaller errors than 1/20th. Degree of fine detail is improved slightly, but the -QUANTITY- of this delicate stuff is proportionally larger than the coarse and more easily seen detail. The image 'difference' is relatively large, and quite obvious to anyone seeing the actual comparison.
________
About your off axis mask-
Did you tilt the focuser on that 10F/5.6 when using such a mask???? Do you know -WHY- I am asking this????
About visual acuity-
At what lowest power setting can you reliably see a good tiny diffraction disc? (IE, the brightest, sharpest setting to use for maximum rez possible)???? Other than making detail larger, and a bit easier to see, all magnification does is reduce intensity and contrast which can, and does obscure or render fine detail harder to see, period.
These things I mention, are -NOT- off topic. They pertain to seeing, and not seeing the item of discussion. It has been -YOU- that has brought a negative context to this thread for personal gain from the beginning page after my report of seeing Encke and Trap stars. Again, thanks, Dave.
M.


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Re: Enckes new [Re: Mark Harry]
      #5849516 - 05/09/13 09:02 AM

Quote:

Dave's limit is what he has stated as 1/10th wave. this is where his acuity must "run out" and has himself claimed there is no/-LITTLE- improvement with any accuracy better than that.
I know several individuals who insist (myself included) that there's a noteable difference with optical trains with smaller errors than 1/20th. Degree of fine detail is improved slightly, but the -QUANTITY- of this delicate stuff is proportionally larger than the coarse and more easily seen detail. The image 'difference' is relatively large, and quite obvious to anyone seeing the actual comparison.



Are we comparing apples & oranges here? A rough 1/20 wave RMS optical surface may well be far inferior to a 1/10 wave PV optical serface .... but going past 1/10 wave PV, however rough, the improvements are so small that they're at best very hard to detect ... and even then adding 10% to the aperture will more than compensate for optical "defects" in the 1/6 wave PV range.

Differences between observers' acuity, temperature stabilisation and atmospheric steadiness are much more of an issue when resolution of critical features is concerned.

So far as "Enckes" is concerned: I have no difficulty in accepting that observers with good acuity, a better than average 6" scope and good seeing can see some variation in brightness across the width of the A ring. But what is now known as the Keeler Gap (80-90% of the way from Cassini's Division to the outer edge of the A ring): I don't believe that can be seen properly with less than 12" & full resolution as a sharp edged, black gap takes a lot more than that.


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Re: Enckes new [Re: brianb11213]
      #5850081 - 05/09/13 01:54 PM

Consider D&C conditions, as explained in TEX's book The MAXIMUM deviation, considered as the boundary wavefront; but the MAJORITY of the surface is well under stated tolerance in question. If more amateurs would take this into account, there would be no issues with RMS, Strehl,RTA, -PVW wavefront error-, etc or confusion as to tolerances claimed (this applies to manufacturers to custom optics, as well.)
Many of the readers in these ATM threads fail to take this into account.
Just so happens, I'm likely the only professional in this field who will tell you about it. Many who "know better", will refuse to post any mention for getting their rationale of "garbage" that i've put up with from a certain poster.
**********
And I must caution particularly the condescending poster, communicating details or personal PMs isn't tolerated by the TOSS policy; which isn't really inforced uniformly.
M.

Edited by Mark Harry (05/09/13 01:59 PM)


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Re: Enckes new [Re: brianb11213]
      #5850084 - 05/09/13 01:56 PM

As to your last paragraph, -BINGO-....except for the 12" criteria. FWIW,
M.

Edited by Mark Harry (05/09/13 02:07 PM)


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David Knisely
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Re: Enckes new [Re: Mark Harry]
      #5850104 - 05/09/13 02:08 PM

On Mark Harry's question, yes, the 10 inch Newtonian's focuser is set up so that I can tilt its base. This was necessary whenever I used my DayStar T-Scanner solar H-alpha filtering system (3.5 inch off-axis ERF) on it to allow for a more uniform field of view for the additional optics needed to get the f/30 light cone the T-Scanner requires.

As for the contention that I "attempt to claim fame at someone elses expense, ", well, that has crossed the line. We will let the moderator deal with that.


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Re: Enckes new [Re: David Knisely]
      #5850163 - 05/09/13 02:36 PM

We may at that, David.
Did you tilt it; and at what degree?????????
Specify the degree of compensation.
This will be settled once, and for all.
M.

Edited by Mark Harry (05/09/13 02:38 PM)


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Re: Encke Division new [Re: brianb11213]
      #5850204 - 05/09/13 02:54 PM

Quote:

So far as "Enckes" is concerned: I have no difficulty in accepting that observers with good acuity, a better than average 6" scope and good seeing can see some variation in brightness across the width of the A ring.




Your description is of the Encke Minima, a broad low contrast feature roughly in the middle of the A-Ring. I would describe this feature as trivial in a 10-inch aperture. It was regularly visible in my old, contrast-challenged Meade Starfinder 10-inch equatorial Newtonian. Based on that experience, I see no reason to doubt it can be observed in a good 6-inch aperture.

Quote:

But what is now known as the Keeler Gap (80-90% of the way from Cassini's Division to the outer edge of the A ring): I don't believe that can be seen properly with less than 12" & full resolution as a sharp edged, black gap takes a lot more than that.




The Keeler Gap is a 35 km wide gap located within the A-Ring about 250 km inside the outer edge of the ring. This is roughly 98% the distance from the inner to the outer edge of the ring. The Keeler Gap is not visually observable in any Earth-based telescope.

The Encke Gap (commonly known as the Encke Division prior to 2008) is the 325 km wide gap located roughly 80% of way from the inner edge of the A-Ring to the outer edge. As an aside, the IAU prefers the term, gap, to describe this feature because it resides entirely within the ring. This feature is a challenging visual observation even in very large aperture. What's the smallest aperture capable of discerning this feature? I suspect one could have a lively discussion of that topic

There is, of course, no feature known as "Enckes" and the continued use of the term has generated no shortage of confusion in this thread, beginning with the original post.

Bill in Flag


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azure1961p
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Re: Encke Division new [Re: BillFerris]
      #5850395 - 05/09/13 04:23 PM

Well very obviously Bill there's no such thing as Enckes and being that its definition seems to shift by name depending where its term is originating from Enckes pretty well capped it. Moreover the description of the feature in the OP left no doubt it was not the easily seen minima which is hardly challenging at all. A link to the feature specific was included . No minima present nor 35 kilometer gap.


Pete

Edited by azure1961p (05/09/13 07:02 PM)


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Re: Encke Division new [Re: azure1961p]
      #5851256 - 05/10/13 01:44 AM

Quote:

Well very obviously Bill there's no such thing as Enckes and being that its definition seems to shift by name depending where its term is originating from Enckes pretty well capped it. Moreover the description of the feature in the OP left no doubt it was not the easily seen minima which is hardly challenging at all. A link to the feature specific was included . No minima present nor 35 kilometer gap.


Pete




The problem here is that the IAU named the fine gap in the outer A-ring seen and accurately drawn first by Keeler in 1888 "the Encke Gap", rather than calling it the Keeler gap. This referred to the older original account by Johann Franz Encke in 1837 (and other)s of a division within the A-ring. The "division" was placed in various locations in the ring with some observers drawing multiple divisions and others only one. Encke may have been seeing the contrast feature we refer to as "the Encke Minimum" rather than any gap there. The IAU sort of threw Keeler a "bone" by naming a very very fine gap right near the very outermost edge of the A-ring, "the Keeler gap". However, that gap was only discovered via spacecraft observations. It is kind of a historical mess that really should have been dealt with in a better manner (but hey, we all know what happened to Pluto don't we?). A really good historical summary of the topic can be found on the fine web page by Eric Jameson:

The Encke Minima and Encke Division

Clear skies to you.


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Re: Encke Division new [Re: David Knisely]
      #5851285 - 05/10/13 02:28 AM

Quote:

Encke may have been seeing the contrast feature we refer to as "the Encke Minimum" rather than any gap there. The IAU sort of threw Keeler a "bone" by naming a very very fine gap right near the very outermost edge of the A-ring, "the Keeler gap".



Exactly !


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Re: Encke Division new [Re: leviathan]
      #5851402 - 05/10/13 06:02 AM

To All

Remember one of the basic TOS Rules, PLAY NICE. Cloudy Nights is not a place for personal attacks. Things are getting a bit nasty and this will not be tolerated. Please tone it down or this thread will be locked.

Rich (RLTYS)


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azure1961p
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Re: Encke Division new [Re: Rich (RLTYS)]
      #5851458 - 05/10/13 07:18 AM

Dave,

I'm familiar with Eric's excellent web page on this feature. And you are right the nomenclature is quite the mess historically. If Ive got it right, Enckes never saw the Enckes Gap and Keeler never saw the Keeler Gap.

Thanks again for the link. It is a really nice article.

Pete


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Re: Encke Division new [Re: David Knisely]
      #5851527 - 05/10/13 08:23 AM

I’ve really learned a lot from this tread.

With a new secondary and insanely great seeing for VT I was able for the first time on Saturn to boost the magnification in my 10” Dob to around 400x, 5/14/13. Because of this thread I was trying really hard to see the Encke Division. Never did manage it.

The interesting thing is that I kept seeing a darker line bisecting the A ring. I knew the Gap was near the outer edge of the ring so I just dismissed what I saw as an optical aberration. At that time I didn’t know there was a Encke Minima, or that there was a difference between the two. But now I do!

I also realized that with the excellent mirrors I now have, I’m really going to have to do my home work on what’s possible to observe on Saturn and really knuckle down and pay more attention. I didn’t have any reference material with me because my previous viewings were “nice to look at” but not detail rich. That nights quick look turned into two hours of “WOW I can see all sorts of banding”, and “I wish I knew more about the finer details of ring structure”!


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Re: Encke new [Re: azure1961p]
      #5851647 - 05/10/13 09:44 AM

The correct spelling of the name is, Encke. For those interested, here's a good, basic Wikipedia article about the renowned German astronomer, Johann Franz Encke. Also, a direct link to the A-Ring section of Wikipedia'a article on Saturn's ring system.

Bill in Flag

Quote:

Dave,

I'm familiar with Eric's excellent web page on this feature. And you are right the nomenclature is quite the mess historically. If Ive got it right, Enckes never saw the Enckes Gap and Keeler never saw the Keeler Gap.

Thanks again for the link. It is a really nice article.

Pete




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Re: Encke new [Re: BillFerris]
      #5851701 - 05/10/13 10:19 AM

I was observing with my 6" F10 Jaegers achro, which has proven to be superb. There was no Encke division seen. Cassini's went all the way around during moments of good seeing. B ring had radial contrast features, A ring had a darkening in the outside to middle but the Enke gap eluded me. Seeing was about a 4-5 so I wasn't expecting much.

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Re: Encke new [Re: bremms]
      #5851910 - 05/10/13 12:18 PM

Ill bet its superb and I wouldn't want to suggest a given feature such as Enckes* not appearing is indicative of anything short of a great view. I'm 50/50 that I may ever see it with my 8" but Im slightly optimistic my boundary layer fan makes it at least a more compelling challenge. Ill bet your views were all that.

Pete

Bill: I followed Enckes with an "s" the same way one might say Bills or Petes or Pauls respective feature. I'd be happy to help in PM if this becomes problematic.

Cheers.

Edited by azure1961p (05/10/13 12:20 PM)


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Re: Encke new [Re: azure1961p]
      #5852207 - 05/10/13 03:15 PM

Pete, I would think you have a chance with superb seeing with such a good 8" scope. Properly it should be Encke's division or the Encke division. Enckes division would be plural.

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Re: Encke new [Re: bremms]
      #5852519 - 05/10/13 06:51 PM

Ahhhh thanks for the tip - and encouragement!

Pete


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Re: Encke Division new [Re: BSJ]
      #5852526 - 05/10/13 06:55 PM

Quote:

I’ve really learned a lot from this tread.

With a new secondary and insanely great seeing for VT I was able for the first time on Saturn to boost the magnification in my 10” Dob to around 400x, 5/14/13. Because of this thread I was trying really hard to see the Encke Division. Never did manage it.

The interesting thing is that I kept seeing a darker line bisecting the A ring. I knew the Gap was near the outer edge of the ring so I just dismissed what I saw as an optical aberration. At that time I didn’t know there was a Encke Minima, or that there was a difference between the two. But now I do!

I also realized that with the excellent mirrors I now have, I’m really going to have to do my home work on what’s possible to observe on Saturn and really knuckle down and pay more attention. I didn’t have any reference material with me because my previous viewings were “nice to look at” but not detail rich. That nights quick look turned into two hours of “WOW I can see all sorts of banding”, and “I wish I knew more about the finer details of ring structure”!




Brian I wish you all the luck. As I mentioned in another post its still a great view without the E-gap (heh take THAT Bill!). Still how can you NOT look for it? You have the golden key aperture apparently under the better circumstances. Hang in there and I look forward to your reports. And u kno how it is - even a negative result is a positive observation!

Pete


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Re: Enckes new [Re: rgm40]
      #5853396 - 05/11/13 08:58 AM

I do remember from the late 70's early 80's warm misty 4am till dawn planet viewing leaving the RV6 set up from the evening with a loose cover and getting the best images of Jupiter Saturn and Mars with a couple 9-10/10 seeing mornings.

I can see the A ring darkening easily, thought we glimpsed the Encke division in a 16" F5 Cave(backyard observatory of a friend of a friend)but the seeing went sour that evening.
Great mirror in that Cave, but seeing never cooperated when we went to observe with him. (The beer probably didn't help either)


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Re: Enckes new [Re: bremms]
      #5890294 - 05/29/13 07:44 AM

This is very interesting...

An excellent imager in South America with a C8 has successfully imaged Enckes almost to the point I thought it was via C11 or C14. His name is
Rafael Defavari and he's something on par with Damien Peach with an 8.

I thought it shed light on the Enckes Division question with an 8". Wether or not the eye can detect the low levels of contrast Rafael has is still a point of contention among some, but with the imager its at least there as a line on SOME level. I'm to locate the smallest aperture that can still image it but it looks like it ends with c8. I'd wonder if a 150 Mak in Rafael's hands (and seeing) would show it but for now there's no one making pix to his level of clarity as the rings are wrought with ringing effects and softness comparably.

Here's the link:

http://500px.com/rafaeldefavari

Pete

Edited by azure1961p (05/29/13 07:46 AM)


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leviathan
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Re: Enckes new [Re: azure1961p]
      #5890300 - 05/29/13 07:59 AM

Pete, astrophoto is another story. I saw several Encke's imaged with 8".

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Re: Encke Division new [Re: BillFerris]
      #5890432 - 05/29/13 10:11 AM

Quote:

Quote:



Your description is of the Encke Minima, a broad low contrast feature roughly in the middle of the A-Ring. I would describe this feature as trivial in a 10-inch aperture. It was regularly visible in my old, contrast-challenged Meade Starfinder 10-inch equatorial Newtonian. Based on that experience, I see no reason to doubt it can be observed in a good 6-inch aperture.

Bill in Flag




Recently I read an article in the latest Astronomy magazine where the author said he'd seen Encke's Minima in a 4" reflector.


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Ziggy943
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Reged: 08/11/06

Loc: Utah
Re: Encke Division new [Re: Schaden]
      #5893499 - 05/31/13 01:04 AM

Although I have met him only a couple of times, I count John Pons among my friends. He related to me and observation of Encke's division through an 8" refractor. I forget the name of the owner but he said Encke's was visible all around. I have no reason to doubt John's observation.

As stated ealier in this thread, I have seen it twice in my 9" Clark.


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Mark Harry
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Reged: 09/05/05

Loc: Northeast USA
Re: Encke Division new [Re: Ziggy943]
      #5909240 - 06/08/13 06:39 AM

Thanks for posting that, Ziggy.
M.


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E_Look
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Reged: 03/06/08

Loc: near New York
Re: Encke Division new [Re: Mark Harry]
      #5910443 - 06/08/13 09:27 PM

Ziggy, would that be true through a 8" reFLEctor?

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Starry eyes
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Reged: 04/30/10

Re: Encke Division new [Re: E_Look]
      #5926760 - 06/18/13 01:47 AM

I hesitate to add my two cents worth but... Over the course of several decades I have seen Encke division and shown it to others fairly often with a 6.75" off axis mask on a 18" split ring equatorial. I attribute this to a effective slow F ratio, a smooth mirror, unobstructed aperture, Naglers, great seeing in California's coastal mountains, an extremely steady mount with tracking, great ergonomics for the eyepiece giving a comfortable view, and, I guess we didn't know better. Never could trace it all the way around. I bring this up to demonstrate that perhaps there are a few more factors to consider in this civil discussion about the interaction of the human eye.

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