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Geoff Barnes

The Alpine Valley

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I've been pushing my 12 inch Dobsonian to its limits lately to see just what it is capable of.

E and F in the Trapezium have been relatively easy targets this last few sessions, and Sirius B whilst not easy because of Sirius' brightness, was also clearly there.

Tonight I decided to study the Moon, and in particular Vallis Alpes, the Alpine Valley. The Valley itself is of course an easy target, but I was more interested in seeing the Rille that runs through the centre of the valley, which I understand is quite a challenge.

I started with the Baader zoom, tried all magnifications available but alas saw no sign of the Rille.

Time to bring out the big guns, the Morpheus 6.5mm first, quite a bit bigger in the EP now but still no sign of the Rille.

Okay out with the Explore Scientific 4.7mm 82 degrees, surely this is the one. Nope, nothing!

Only one thing left, the 2x Celestron Ultima Barlow, tried it with all 3 EP's right up to 535x (which was hopeless), still nothing.

A complete failure, although good fun trying!

So, I'm left with the probable explanation that the elusive Rille is probably only fleetingly visible when it is right near the terminator and a shadow is cast in it. Probably if I had tried last night or the night before I may have seen it?

Can others who have had success confirm this please?

 

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Despite others  seeing the central rille with quite modest apertures, this feature eluded me until last year when a combination of good seeing and the right timing of the lunar sequence finally showed it in my 16" SCT after decades of searching for it. Surprisingly, my 20" Dob next to it didn't show it at the same time.    🙂

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You do need a certain lighting to give the best chances to see that central rille. I've done it a few times with my 12" F/5.3 dob and it's consistently been the Pentax XW 5mm that has done the job at 318x. This is a target that comes and goes as the seeing changes slightly and certain parts of the rille stand out more than others. I've not (yet) had a night where I've seen the whole length of it.

Last night here would probably have been a decent one to try this but I had a 4 inch refractor out instead of the dob :rolleyes2:

If you keep at it, I'm sure you will get this tough feature.

By the way, how high is Sirius above the horizon when you observe it ?. Here it's pretty low and I only see it for an hour when it pops out from behind our neighbours house and before it goes behind some large trees. Certainly adds to the challenge of seeing that pesky little "pup" star !

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Hi Geoff.
I was out last night and spent some time trying to see the rille. From @John's comments above I guess I haven't much chance with my eight inches but will keep trying. 
Good luck Geoff, keep trying it would seem you have the arsenal for this elusive feature.

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3 hours ago, John said:

By the way, how high is Sirius above the horizon

Hi John, because we're nearer the equator than you Sirius gets up quite high at this time of year, I would guess about 60 degrees or so recently, so a good height for observing.

I should have added that the seeing was quite unsteady last night after a hot 36 degree day, so lots of thermals moving around up there!

Edited by Geoff Barnes
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The only scope I have seen the rille with is my 16" dob. I agree with the comment that the light has to be right and also the seeing needs to be steady.

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I've seen it in a Tak FS 128mm refractor with a mono eyepiece, but the best view I've ever had of the central rille has been through my FC100DC with a binoviewer, X2 Ultima Barlow and a pair of 15mm Vixen LV's. The valley floor was reasonably well lit, so you'd expect the chances of seeing the rille to be virtually none. However, the central rille appeared as a fine, bright, broken scalpel cut. Steady seeing and a sharp image seem to be more important than aperture. I think using both eyes helped me a great deal too. In fact, I seem to recall another SGL observer commented that he thought he saw it on the same night that I did. I could be wrong but in my mind I thought it was perhaps paulastro, John or Stu? Sadly I did not sketch it on the night in question, but I have found a rough sketch from 2015 that roughly illustrates the eyepiece view. (Ignor the inaccurate valley walls. I was only interested in sketching the position and look of the rille itself, and this sketch was never meant to be seen by others). Note the rille is slightly towards the S wall in the sketch. There is also an easily seen dark fine rille cutting across the valley width, which can be traced through the mountains to the north where it divides several times, and eventually links to a rille that runs along the shore of Mare Frigoris.

1611992848_2019-01-1523_05_37.thumb.jpg.d3b6cfb81f6f7aa944b92df5d7b941e5.jpg

Edited by mikeDnight
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Nice image of this feature here showing the dimensions:

post-64701-14073688379949.jpg

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I imagine the rille is difficult because it doesn't run N/S, so it doesn't appear as a harsh black line but more often is lit by the Sun and so appears slightly brighter than the basalt floor of the valley. Just my theory!

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40 minutes ago, mikeDnight said:

There is also an easily seen dark fine rille cutting across the valley

 Yes Mike I saw that feature in the centre of the valley, it was faint but definitely there.

I'll try again when the atmosphere is a bit less turbulent.

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I set out last night determined to see the Alpine Rille, a feature that eluded me last time.

Conditions were clear but is was a bit windy so seeing was rather wobbly.

The valley itself was beautifully clear with the shadow of the southern edge defining the whole length of the feature.

The shadow was in the end to be my downfall though. The whole western half of the valley was in complete shade, and  the eastern half had shade about half way across decreasing to zero at the eastern end.

So I concentrated on that half of the valley and took increasing magnification, eventually  right up to 460x with my Baader Morpheus 6.5mm barlowed 2x. 

The valley was very large at this mag. but the seeing was completely hopeless wobbling about so much with the unstable atmosphere I just couldn't fix my focus on it long enough to see the rille. 

I'm determined to try again tonight when the valley shadow should be clear of the valley floor and winds are predicted to be lighter. It's tonight or I'm going to have to wait another month.

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Good luck with this elusive feature. I hope you persistence is rewarded.

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Keep at it Geoff :smiley:

I find the illumination of the valley floor and the seeing need to be "just right" to catch this ellusive feature. Each time that I've done it, I've found that 318x (Pentax XW 5mm) has proved the most effective with my 12 inch dob. I've tended to see sections of it where it's at it's most prominent rather than the whole length and they tend to pop in and out of visibility as the seeing fluctuates.

Certainly a very tough challenge !

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Well the seeing was still a bit too wobbly, but skies were clear and I spent about 2 hours just concentrating on the Rille. 

Started in broad daylight with the sun still up to try and catch the rille with a bit of shadow still in it, but not to be, too bright and too faint, better to wait a bit until dusk falls.

Back to the scope as darkness descended and after experimenting with various eyepieces, settled on the Baader zoom on 8mm with the 2x Ultima Barlow for a magnification of about 375x. The view was much sharper and brighter now but the seeing was infuriatingly wobbly. Just occasionally the view would clear and for a brief few seconds everything was sharp. I thought I saw it, western end of the valley there was definitely the hint of a line, as faint as a thread of a spiders web, in the middle of the valley. Then back to wobbly and fuzzy. I waited again for the next settled view, it took a long time but again it suddenly became clear and sharp and I stared at the western half of the valley. Yes, the finest faintest thread was there, from the left hand end right through to about half way across to the middle of the valley. There it disappeared and no sign of it on the eastern half no matter how hard I looked. But I saw it, definitely saw it, but oh so fine, almost not there, but I saw it, yay! :hello2:

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Well done Geoff. It's a great sense of satisfaction and achievement when all the effort to tease out detail finally pays off.

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This is actually one of Mike's observations that I CAN match! I have seen the rille in my Tak, which really surprised me as it has eluded me in every other scope. I guess just a combination of good seeing and illumination, but my views match Mike's description very closely.

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Here is a detailed photo of the valley and the rille which might help confirm which section you glimpsed:

 

post-64701-14073688379949.jpg

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2 hours ago, Stu said:

This is actually one of Mike's observations that I CAN match! I have seen the rille in my Tak, which really surprised me as it has eluded me in every other scope. I guess just a combination of good seeing and illumination, but my views match Mike's description very closely.

Thats a great result Stu - so far it's only the 12 inch dob that has shown me this feature. I have hopes for the LZOS/TMB 130 triplet with this regard though.

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1 hour ago, John said:

Here is a detailed photo of the valley and the rille which might help confirm which section you glimpsed:

 

post-64701-14073688379949.jpg

 

What I saw of the rille, albeit fleetingly, was from the left hand end of the valley all.the way to about the middle where that odd circular feature ( a crater?) bisects it. The right hand end on the other side of that feature was blank, no sign of it at all.

It was probably the hardest object Ive succeeded in seeing so far, maybe on a par with Saturn's moon Enceladus which also was incredibly faint.

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I just caught a bit of it this evening in the Mak, starting at the left end and probably a little under half of what you describe Geoff. Will try again in a minute, just eating!

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It would have been a good Plato / Alpine Valley observing night here tonight if it was not for a thin layer of cloud. I had some nice views of the moon with Rupes Recta and the Apennine Mountains showing well but magnification much above 80x was pointless due to the hazy cloud. So I stuck to gazing at low to medium magnifications instead. My Orion star count was zero tonight - just the 4 corner stars visible and even those were faint !

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As an aside, while I had the high power EP in I had a quick look at a couple of other targets, which ended up with me thinking I had double vision when I focussed on Alnitak and saw two stars, one above the other. I couldn't split them as there was far too much glare and they were very close together, but definitely two stars of equal magnitude it seemed. Another first for me.

Edited by Geoff Barnes
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39 minutes ago, Geoff Barnes said:

As an aside, while I had the high power EP in I had a quick look at a couple of other targets, which ended up with me thinking I had double vision when I focussed on Alnitak and saw two stars, one above the other. I couldn't split them as there was far too much glare and they were very close together, but definitely two stars of equal magnitude it seemed. Another first for me.

It's a nice double. Probably easier to split with a refractor than a newt to be honest. Clean, diffraction-free star images help a lot !

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