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#1 azure1961p

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Posted 06 April 2013 - 10:57 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

#2 David Knisely

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Posted 07 April 2013 - 01:20 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.

#3 BillFerris

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Posted 07 April 2013 - 01:43 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

#4 azure1961p

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Posted 07 April 2013 - 05:17 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.cloudynig...&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

#5 idp

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Posted 11 April 2013 - 10:21 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

#6 azure1961p

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Posted 11 April 2013 - 11:15 AM

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

#7 idp

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Posted 11 April 2013 - 12:36 PM

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 :mad:

#8 azure1961p

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Posted 11 April 2013 - 01:01 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

#9 David Knisely

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Posted 11 April 2013 - 01:03 PM

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.

#10 azure1961p

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Posted 11 April 2013 - 10:55 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".


#11 idp

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Posted 12 April 2013 - 08:58 AM

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

#12 azure1961p

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Posted 12 April 2013 - 10:24 AM

Nevertheless Im not hopeless on the matter!

Pete

#13 David Gray

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Posted 12 April 2013 - 11:18 AM

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

Attached Files



#14 idp

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Posted 13 April 2013 - 07:20 AM

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....dObCTkey.html?1

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

Ivano

#15 idp

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Posted 13 April 2013 - 07:29 AM

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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#16 azure1961p

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Posted 13 April 2013 - 08:05 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.cloudynig...&password=&a...

#17 idp

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Posted 13 April 2013 - 08:50 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

#18 azure1961p

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Posted 13 April 2013 - 09:04 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

#19 Asbytec

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Posted 13 April 2013 - 01:44 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.

#20 rgm40

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Posted 16 April 2013 - 08:03 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.

#21 buddyjesus

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Posted 16 April 2013 - 09:46 PM

happy you made lemonade out of lemons rgm

#22 Ziggy943

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Posted 17 April 2013 - 12:06 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.


#23 george golitzin

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Posted 17 April 2013 - 04:17 AM

... 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

#24 Peter Natscher

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Posted 17 April 2013 - 09:18 PM

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: 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

Attached Files



#25 azure1961p

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Posted 17 April 2013 - 09:43 PM

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

Pete






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