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Mark Harry
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Reged: 09/05/05

Loc: Northeast USA
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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Mark Harry
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Reged: 09/05/05

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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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Reged: 04/19/04

Loc: southeastern Nebraska
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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Mark Harry
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Reged: 09/05/05

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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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BillFerris
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Reged: 07/17/04

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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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Reged: 01/17/09

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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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David Knisely
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Reged: 04/19/04

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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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leviathan
sage


Reged: 11/29/11

Loc: Azerbaijan
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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Rich (RLTYS)Moderator
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Reged: 12/18/04

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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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Reged: 01/17/09

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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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BSJ
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Reged: 12/22/08

Loc: Grand Isle, VT
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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BillFerris
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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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bremms
Carpal Tunnel
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Reged: 08/31/12

Loc: SC
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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azure1961p
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Reged: 01/17/09

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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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bremms
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Reged: 08/31/12

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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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azure1961p
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Reged: 01/17/09

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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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azure1961p
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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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bremms
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Reged: 08/31/12

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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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azure1961p
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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
sage


Reged: 11/29/11

Loc: Azerbaijan
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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