Plato Craterlets & Alpine Valley.

[Geoff Barnes]

Finally got a couple of clear nights this week and was keen to get a proper first light with my Vixen SLV 2.5mm EP, which I bought way back in February.

Sunday night was cold and clear and completely still and I was expecting perfect seeing for some high power views of the moon. Alas, while transparency was great (I gave it 10:10) the seeing was inexplicably very wobbly, even at moderate powers with the Baader zoom at 8mm (you just can never tell regarding the seeing).

Plato was still just in shadow beyond the terminator so all my concentration was focused on the Alpine Valley which had just come into the sun's light. The shadow of the southern rim was nearly half way across the valley at the western end, tapering off at the other end to almost nothing so conditions were right for a good chance to see the Alpine Rille. I had the 12 inch Dob in tracking mode so the Valley filled the centre of my FOV and stayed there. I had my 4mm SLV in first giving 375x and this gave occasional tantalising glimpses of the western end of the rille when the seeing steadied for a second or two, but was just too wobbly for anything more. Replacing it with the 2.5mm SLV yielding a crazy 600x magnification naturally produced terribly shaky seeing, but the image was obviously much larger now and I persevered for a couple of hours just hoping for a steadier view. I would reckon I had three or four chances each for a few seconds in which I'm sure I could see the rille all the way along the valley, but the glimpses were so brief it was hard to be sure.

Monday night produced equally clear cold and calm conditions and out I ventured again, this time knowing Plato would be in view. I had never seen the Craterlets before and this was to be my goal for the evening. Centred on axis again in tracking mode I again used the 4mm SLV to begin with and again the seeing was frustratingly wobbly, not quite as bad as the previous night though and almost instantly I could see the crater floor of Plato was not smooth as it had always appeared to me in previous sessions. In steadier moments I could make out A,B,C and D craterlets and thought I could see E over on the left but not sure, F was in hidden in the long jagged shadows cast by the crater rim walls.

Swapping over with the 2.5mm again the view became more wobbly but with perseverance I was thrilled to see the four main craterlets as obvious circles and E craterlet for brief seconds appeared as a white dot. Poor seeing didn't allow any more to be seen but I was happy with my haul.

What was also nice to see was both Plato and the Alpine Valley in the same FOV with the SLV's and I enjoyed switching my gaze from one to the other. The Alpine Rille was in much more sunlight now and it was harder to see with less shadow, though there were hints of it as the thinnest white thread in the steadier moments.

So all in all a successful foray and I can't wait for a chance to return to these wonderful lunar features with the benefit of rock steady seeing when I'm sure the SLV's will deliver the goods. It was just so good to be back out observing again, opportunities here in winter are few and far between up on the mountain.   

[chiltonstar]

4 minutes ago, Geoff Barnes said:

 

 ............ these wonderful lunar features ........ 

Absolutely! Sounds like a good session.

Chris

[Pete Presland]

Sounds like an excellent session, looking forward to the cold dark winter nights already!

[John]

Great stuff Geoff

Tough targets, that rille and the craterlets, or at least the ones beyond "the big 4". Seeing needs to settle to get those elusive glimpses.

Well worth the effort though and thanks for posting the report