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Uranus in Twilight and Through Cloud!

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#1 David Gray

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Posted 15 July 2013 - 09:57 AM

I’m not looking for any fights with this post: the pros/cons being exchanged almost beyond repetition – ad nauseum even; and any drawings I get will probably be confined to sending to ALPO-Japan and ultimately the BAA. Simply addressing anyone who wants to give it a fair go with the points below being given consideration.

Previously I have banged on a few times about the need to get the light of this planet (and Venus) to a level that does not wash out any very faint features that it may offer. So it was this a.m. that I began the apparition with a check as to how bright it looks in the mono (non binovu). Also now for N hemisphere observers it is getting ever higher each year and an easier naked eye object in decent conditions. This increase I have found to render it too bright even at x535 and that’s with the split light path of the bino! Using the mono view (x485) this morning I found it far too bright (near white at times) and kept it in view for some time with advancing twilight and passing cloud never losing it even when the apodizer was used – demonstrating that with perhaps beyond 250-300mm I would not class this as the faint object it’s sometimes described.

Hopefully the attachment summarises this long-winded preview!

It was also a chance to apply my long-unused excellent 14mm Zeiss-Wildey(!) Monocentric that I used for many years with Uranus on the D-K. The recently obtained 50mm X 80mm extension tube making it more parfocal with the Binos: saving wear and tear on the primary mirror focusing.

Seeing was not good enough justify drawing some fleeting impressions of banding tho’ limb shading was quite certain especially with dimming by the variable cloud and especially when the apodizer was attached. I regard limb-shading detection as just the starting point for seeking the usually more elusive banding or such.

Actually following it into a certain level of twilight may well be advantageous; much as we see the n/e moon detail stand out starkly. More difficult locating the planet in evening twilight but last apparition Dec/Jan I found it fairly easily with the 10x50 finder by sweeping from alpha Aqr: good knowledge of the 6 deg. field essential however.

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#2 David Gray

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Posted 15 July 2013 - 10:30 AM

Thought it as well to elaborate on the Monocentric:


The “Zeiss-Wildey” Monocentric was actually kindly done for me by the late Henry Wildey after I had written him requesting a standard 8mm Monocentric. After a few exchanges he mentioned this “bulky” 14mm one he had come by in the 1940s/50s. This had an unusual diameter, as I recall, of something like 43 to 47mm and he assumed it had a military application of some sort – tho’ ones I have seen have been the wide-field Symmetrical types. I have a 29 mm fl. c.52mm dia. very heavy brass! Anyway he offered to mount it in the standard RAS thread fitting of those days; and charged me the very reasonable sum of 18 shillings and sixpence (18/6, 92.5 pence decimal: c.$2.50 to the £ back then!)

So after I had used it for some weeks he surprisingly wrote offering, as an afterthought, the original body for free so I said ok; but seems it went astray in the post as it never arrived. I used the eyepiece mostly with a Barlow on my 10” f/8 Newtonian (also Wildey optics – signed H. Wildey 1963). I have heard that his later optics were of poorer standard due to his failing eyesight – but never had any complaint with the 10” in 14 years use (1964/78) – now mothballed pending re-coating.

It was only after a couple of years I found that he had signed (in pencil) the Monocentric – inside the eye-end: see attachment! So my very own, possibly unique, Zeiss-Wildey Monocentric; perhaps a collector’s item?! The 43/47mm size would have adapted nicely to the D-K 50mm holder. But as it is, performs excellently.

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#3 stanislas-jean

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Posted 15 July 2013 - 12:51 PM

Interresting trial David regarding Uranus.
Personnally I investigated also last week but I think the conditions were not yet enough for making something consistent, twilight too intense and elevation unsufficient when the sky was still darker and with no acceptable images at 375x in the 235mm. Here the weather is a little cold in morning with a sky hazzy and dusty so transprency mediocre.
We will see later end of july for sure.
Good hope.
Stanislas-Jean

#4 idp

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Posted 16 July 2013 - 10:57 AM

Interesting post, Dave.

I was surprised to read that you actually find Uranus to be too bright. The planet always looked rather dark to me when I observed it in past years with a 10" refractor, I thought a 16" or so would be ideal. I'd certainly rate it as a 12'+ object, but I'd like to hear other people's views.

May I ask you why you specifically ask for a monocentric? I know they were widely used, their main virtue being that you can compensate for the chromatic aberration of a refractor using the eyepiece's own aberration - but you use it with reflectors right?

Regards,

Ivano

#5 stanislas-jean

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Posted 16 July 2013 - 12:09 PM

If this can be usefull for you, the 10" refractor wouldnot exhibit strong chromatic aberration. The 6" F10 didn't.
A light yellow filter W8 or 12 would anneal the rest even at high power (400-500x for the 10").
The yellow increase the image contrast.
My 2 pennies.
Stanislas-Jean

#6 David Gray

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Posted 16 July 2013 - 01:55 PM

I was surprised to read that you actually find Uranus to be too bright.


Too bright in relation to the very weak features it presents, not that there is any dazzle in the usual sense. Not the painful kind I find with Jupiter, even with the binos + apodizer! Some years back I was getting, 30 min or so, with Neptune then straight on to Uranus - the sensory relief I have described as: “after looking at Neptune, Uranus looks relatively huge and almost dazzling”!

The inspiration for this thread was that I could keep it comfortably in view close to some 20 min. before sunrise in a not ideal sky –thin high cloud, tho’ seeing never quite got to letting me be sure of more than limb shading.

I know I am getting a good disk, brightness & seeing-wise when I start to see the limb shading fade off indefinably toward the centre of the planet – true 3D effect and nothing at all do with the binoviewer myth! If I am getting a sharply defined disk and the shading abruptly demarcated or absent, then I have to consider the image too bright and then it stands the apodizer.

The thing when looking at such as Uranus I resist using the light on my drawing board till I have to – much of what I have determined is then in my memory – after all there’s not a lot!! Each apparition I make sure I have it’s position (chart) well memorised to avoid any lighting from the start of a session;; and PC monitors avoided well prior and during!! 44 Psc. made things easier last apparition and as I say the planet is now pretty easy n/e in decent skies – I followed the two last year with the n/e with ease till they blended and parted. Knowing it’s finder field well is important for another reason (avoiding any lights), I feel, as I often go to some nearby star (preferably a tight double) for frequent focus-checks. I have spent some time recently studying the field on SkyMap Pro; and I found Uranus quickly that morning, simply by following (in the finder!) the, memorised, straggly line of sixth mag. stars running south from delta Psc.

Monocentric: back in my early observing days I got a hankering for one after reading such as Sidgwick (Handbook), Peek (Jupiter book) and of course S&T as being a good planetary eyepiece tho’ small field. At the time my main one with the 10” Newt. was a 6mm Orthoscopic (x330) so as I said I sought an 8mm (x250) Mono. to supplement it in poorer conditions. But Wildey only had the aforementioned 14mm (x140) so finally settled for it – probably that name: Zeiss was a factor!

Even back then they seemed hard to obtain - probably the small field went against it. After the D-K came along (1978) I found it ideal for such as Uranus and tight doubles. Straight in the focuser it gave x474 (exit pupil measures –means of several: I now round to the nearest 5!) Now with the increased light path (Amici) I measure it at x485. Similarly my twin Meade 20mm 5000s give x335 straight in and x365 (Amici+binos)
Regards, Dave.

Edit Note: just recalled why I went to Wildey; as there was a warning out then that some where using the field triplet of an Orthoscopic and passing them off (more expensively) as Monocentrics!!

#7 stanislas-jean

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Posted 18 July 2013 - 02:34 AM

I did some investigation about the apodiser mask based on the
telescope-optics.net for the apodizing mask topic.
All the explanations found into are coming from De Suiter evaluations and calculations.
I enclose at the bottom a table sheet giving data exhibiting the contrast transfer of some scopes considered with perfect optics.
With regards to the standard eye properties (found on the same website) the vision ability corresponds to 10 cycles per (°) of FOV under mesopic vision and 1% threeshold contrast level.
For a trained vision.
Between 6 and 16" aperture the contrast transfer increases from 51,7 to 74.1% sothat from the 2% supposed feature contrast found on planet this involves for the standard eye 1% for 6" to 1.48% for 16" and 1.7% with an optimum apodiser mask. Physically this express the fact that the 16" with apodiser corresponds to 32" without apodiser use.
Supposing the seeing perfect for all apertures for contrast perception of the expressed contrast levels.
In an other hand this correspond to be a slight improvement (evaluated to be 1.15x more in terms of contrasts levels or for expressing a feeling of the improvement the same effect involved by the supression of L/6 spherical aberration).
In first approach it seems useless this filter mask use, but I think for so weak signals we meet on Uranus this can be an help for capturing something around of a threeshold (that depends on own capacities).
I tried to fix this threeshold for my own with the use of several apertures well optically characterised (defined as the corresponding equivalent perfect aperture) in order to locate abilities. For my own the use of 6-8" correspond to the threeshold. This will be different for an other observer indeed as the vision ability can be different.
As a conclusion the use of the mask may help for being above a certain threeshold and for capturing weak features.
This is my expertise of the situation.
Hope this bring some help about the mask use.
Stanislas-Jean

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#8 David Gray

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Posted 18 July 2013 - 07:54 AM

Thanks Stan,

I’ve accrued quite a bit of info on the apodizer – pro & con.! In spite of the arguments whether it works or not; as a neutral filter it certainly works for me. Simply, if I see an improvement when applying it I’ll leave it on – if not I’ll remove it! As I have said elsewhere mine are more “mock-apodizers” as there is no clear central area nor any graduated overlapping offset layers – just a single sheet. I have used a stainless steel flour sieve (1mm square mesh) to advantage for many years, and easy to affix/remove as it fits comfortably (drops) in the end of the D-K. Not that I would not like a proper one!

As I am indicating: preferable to a so-called neutral filter for the colour renditions I attempt. I have a Celestron polarising set but I find this far from neutral – almost as blue as W#80A I find.

However what you write is pertinent to the underlying theme of this thread re. the optimum brightness of the planet to bring out those borderline features. I found it interesting back in 2010 when many were using nearby Jupiter as an easy location point for getting Uranus. If they were spending time with the former then viewing Uranus straight after, perhaps one reason we were getting so many disappointed reactions from those who have bothered little with Uranus otherwise? In fact they were possibly getting the reverse of what I experienced, as I stated earlier in this thread to Ivano: “after looking at Neptune, Uranus looks relatively huge and almost dazzling”! Also related here in 2008 http://alpo-j.asahik...08/u081016z.htm :though I cringe seeing this scan now as I had all sorts of problems retaining the delicate contrasts of drawings - which has now been addressed/resolved, more recently, by resorting to a digital camera-grab of the drawing

As related on the “cassini division” thread (page 2): http://www.cloudynig...5795208/page...
I was doing some investigating of it’s visibility in front of Saturn. Part of this was using a 6” off-axis diaphragm on the D-K and had applied the flour sieve/apodizer which helped little. As a whim I applied a 6” strainer and was astonished to get my best apodizer result ever. This left me perplexed as the mesh was virtually identical to the flour sieve! Then it occurred to me that the dome-shape of the strainer was the clue. Similar to the conventional apodizer the light is gradually diminished from centre to edge: in the case of a hemisphere this is effected by the increasing foreshortening of the mesh as seen by the ’scope. As this is a smoother gradual effect it leads me to wonder if this is the actual shape an apodizer should be, and presumably the central clear area/hole would still be required?. Though the practicalities for larger apertures might be challenging. Also I have since wondered if a truncated/open-ended cone would work! When I get the time and materials I hope to experiment further on this.

Regards, David.

#9 stanislas-jean

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Posted 18 July 2013 - 09:49 AM

There is also a fact that can concur in favor of the mask improvement.
As the telscope-optics.net website more than suggests for the disparition of the first diffraction rings on a point feature with masks, this is the fact that with regards to the planet brightness even at high power the diffraction rings brightness will be difficult to catch in addition. Therefore the contrast gain will be present, relatively, but here.
The vision under twighlight conditions will conduct to contrast lost under beyond certain light background levels. The vision capacity may be altered by the backgound light around the planet.
Under so weak feature presence, mostly it is considered than city lighting conditions doesnot affect the planet feature perception; in fact on Uranus, the vision is affected relatively.
The best conditions are required, seeing indeed, but also a black sky and an excellent sky transparency for optimum results.
The few numbers spreaded on the tablesheet are for perfect conditions, perfect optics, perfect seeing, sothat any parameter decreasing the optimum will be on deduction.
This is since some long times that I researched the situation of the problem, the 2% contrast level was evaluated from the Uranus spectrums published since years and methane absoption rays. This is not thick but here.
Still waiting windows on sky for starting the campain.
Hope this will here.
Good skies.
Stanislas-Jean

#10 idp

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Posted 18 July 2013 - 10:57 AM

In spite of the arguments whether it works or not; as a neutral filter it certainly works for me. Simply, if I see an improvement when applying it I’ll leave it on – if not I’ll remove it!


And that's all that counts!

Too often I've read discussions where experience was quickly dismissed on the grounds that... well, the theory says otherwise, so observers must be wrong!

Stan: yes a big classic refractor has a big chromatic aberration compared to a small one. Yet, a 6" is a 6" and a 10" is a 10" and vastly superior, hands down and chromatic aberration notwithstanding. Not that you perceive much of it anyway at 500x on a planet like Uranus, where you can barely tell the edge of the disk. Not sure that putting up a filter and giving up even more light is a bright (pun intended) idea!

But I'll follow David's wise tip: look at Neptune first, and observing Uranus will be solace rather than misery.

Regards,

Ivano

#11 stanislas-jean

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Posted 19 July 2013 - 12:49 AM

Don't know to which kind of theory you are speaking about.
For the apodiser mask this is coming from Mr De Suiter who through the article suggests some mask design and calculated so expected results with.
When the observations join a certain level from the theory, we can be in the way of confidence.
Regarding the 10", don't know if F15 but considered here as, if we compare with the 6" F10, I had, you should get 11% more CA. I don't think this is strongly difficult to manage, otherwise somthing comes in addition. Mine is L/6.5 in red channel with goods results still in blue channel. It is average good in RGB channels. What about yours?
Regarding the magnification to be used, the 500x, rather 400x for 10" is coming of the fact that for capturing weak features on relatively low light levels the right magnification is to be expected (eye properties) and for annealing the light glare (yes we have light glare fitgh to assum).
Now we know that generally gents are not convinced by the filter use. Because are waiting for night and day results.
This is never that but readibility is improved but what is aimed is the picture in color channel, nothing else, and the benefit is to reduce the CA.
I observed in a 330mm refractor with present CA and frankly this is not a big concern.
Think observations with color filters to see what happen in the different channels (this is not the same results).
I observed Mars with a 6" F6.5 achromat during 2 oppositions under 330x with no concern (with front lens aspherised).
During the last great dust storm of Mars, syrtis major was not percieved majorily by the observers, personnally it was still with a 100mm refractor and 200x near the backgroung level of the disk. The dust density at the maximum intensity was something like 96-97% absorption. What that means?
People majorily didnot catch the 3% contrast levels and under good lighting conditions. For Uranus and Neptune (Neptune with stronger contrasts, relatively) the fitgh is lost by advance.
So 400-500x are needed for the 10" for the reasons given and with filtering.
Don't expect night and day effect with devices we are speaking.
Keep in mind the observer who fixed the Uranus rotation period with a 9" clark refractor, achromat only.
Stanislas-Jean

#12 krakatoa1883

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Posted 21 July 2013 - 10:48 AM

Actually following it into a certain level of twilight may well be advantageous;

Hello David

Giovanni Schiaparelli was used to observe Uranus (and Saturn) in twilight too, he wrote the air was steadier and details clearer compared to darkness. He also made drawings of Uranus showing bands and polar caps although he was mostly interested in determining the apparent diameter of the disc. Some of his remarks on the visual appearance of the planet can be found in the Astr. Nachr.
Regards

#13 David Gray

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Posted 21 July 2013 - 11:46 AM

Hello & Thanks Raf,

Yes I was quite surprised to follow Uranus so deep into twilight and especially given the thin variable cloud. If only the seeing was that bit better! I followed it similarly on a couple of occasions last apparition, in good skies; that was with the binoviewer attached, but not for such a length of time. Also a surprise that it did not become ill-contrasted/washed-out as Jupiter & Saturn tend to do in such circumstances. Though I have had some astounding views of both in darker twilight over the years

I seem to recall seeing Schiaparelli's twilight observations of Uranus somewhere on the web - I will see if I can seek it out again.

Hopefully I will get another opportunity to follow it again into twilight - tho' may abandon it if I see Mars & Jupiter pop over the fence!

David.

#14 Asbytec

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Posted 22 July 2013 - 06:17 AM

"No such thing as a boring planet."

Sometimes Earth is...

#15 David Gray

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Posted 22 July 2013 - 06:32 AM

"No such thing as a boring planet."

Sometimes Earth is...


Perhaps that is why I keep 'escaping to' the others!

#16 krakatoa1883

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Posted 22 July 2013 - 02:46 PM

I seem to recall seeing Schiaparelli's twilight observations of Uranus somewhere on the web - I will see if I can seek it out again.


David, the published work on Uranus (in Italian) can be read here

web page

After many measures of the disc diameter carried out with the 218 mm refractor, in the mentioned paper Schiaparelli wrote that he clearly observed spots and colours on the disc but for a useful work a larger instrument would have needed. He later returned to observe the planet with the 49 cm Merz-Repsold refractor in his late career as director of Brera observatory, but as far as I know he did not publish the results in the international literature. However I have been able to photograph his drawings reported in his original observing notebooks collected in Brera library. Unfortunately as I took this photos for research purposes I have no permission to publish them here, I can only say that they closely resemble modern amateur drawings including your ones :waytogo:

#17 azure1961p

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Posted 22 July 2013 - 06:14 PM

Earth would actually be a wild planet to observe, say, from Mars. And the color! Of course greater aperture would brig the blues out better than small and the contrast of the water to land would lend a warm cast to the land forms .

Pete

#18 Astrojensen

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Posted 23 July 2013 - 01:32 AM

It would be even better from Venus, if you could get above the clouds and heat. And sulphuric acid...


Clear skies!
Thomas, Denmark

#19 azure1961p

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Posted 23 July 2013 - 06:54 AM

Yeah - the acid would be rough on the coatings.

Pete

#20 David Gray

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Posted 24 July 2013 - 06:54 AM

Raf,
My thanks for the further information: can get a little from the link - tho' my Italian is very poor to virtually nil!

I have Alexander's "The Planet Uranus" and seen his mention of Schiaparelli's frustrations with the 20cm Merz and had wondered from that if he tackled Uranus with the larger refractor - good to know he did, and with apparent success! Alexander, it seems, missed this.

Hoping for some clear skies in the coming days - but they keep revising the forecast.

Thanks again.
David.

#21 blb

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Posted 24 July 2013 - 09:55 AM

Earth would actually be a wild planet to observe, say, from Mars. And the color! Of course greater aperture would brig the blues out better than small and the contrast of the water to land would lend a warm cast to the land forms.

Of cource they could, if they could see the surface of our planet which has been covered in clouds for months if not years. They would probably never be able to see the surface where I live without a cloud filter.

#22 David Gray

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Posted 24 July 2013 - 10:57 AM

Gentlemen: the the theme of this thread is plain enough; and I am quite happy to accept that it has run its course.

Disagree with it, refute, ignore or shun it as you will; but at least respect it thank you.

While I appreciated the wit of Norme’s remark I did not think (naively!) that my response would be taken as a licence for changing direction!

"Cloudy Nights Terms of Service"“

"Appropriate posting practices:"

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#23 idp

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Posted 24 July 2013 - 03:07 PM

So let's go back to Uranus!

Yep I've also seen and photographed some of Schiaparelli's observations of Uranus. A sketck I have on my HD was actually done by his assistant, Formioni. I agree with Raf that they closely resemble modern visual observations, and with Schiaparelli that a larger instrument than a 8" something would be needed! :)

Ivano

p.s. I do not believe that privately sharing that material for research purposes would be an infringement of copyright.

#24 azure1961p

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Posted 24 July 2013 - 11:13 PM

Oh tell me about it Buddy. Its been a hazy cloudy summer here. How's the wife and kids??

Pete

#25 stanislas-jean

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Posted 25 July 2013 - 12:36 AM

8" would be preferable.
This is sure, but through a scope this is the contrast transfer ratio that is in cause and for the observer the contrast perception specific to each observer (so above or under the threeshold of perception for an observer).
The eye is sensitive to contrast level depending of the size indeed and of the light level of the object, seeing and sky transparency not considered for the moment.
It is difficult to admit and recall these points, that needs to be investigated in parallel with observations.
Stanislas-Jean






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