Plato and the Alpine Valley

[John]

The illumination angle on the moon was ideal this evening for viewing the Alpine Valley and Plato on the shores of the Mare Imbrium.

I was using my 6" F/8 achro refractor fitted with the Aries Chromacor O-1 which substantially reduces chromatic abberation (CA) and more or less neutralises the under-correction in the scopes optics.

At the lunar limb CA was more or less eliminated at focus with a thin purple line showing inside focus and a pale green line outside focus. Craters on the terminator were filled with black shadows with no purple fringing visible which can obsure the really fine details.

Another effect of the Chromacor is that it enables the scope to exceed the 300x barrier with 342x (3.5mm Nagler) maintaining crisp, detailed and contrasty images. Without the Chromacor I've found there to be not much point in using more than 250x or so as things used to get noticably "mushy" beyond there.

So the Chromacor has been money well spent

Last night and this evening with the Alpine Valley I was concentrating on trying to see signs of the thin rille that runs up the valley floor. On both sessions I've had to conclude that I've not seen anything definate of it, despite the valley being beautifully illuminated for it's whole length. So I've more work to do on that one

The vast lava-filled crater Plato was in the shadows yesterday for much of the evening however it is wonderfully illuminated tonight so I was able to explore it's complex walls with their terracing and slumping and the flat, dark floor. I was very pleased to be able to pick out 3 of the famed craterlets - not just as bright spots but actually as crater pits with tiny dark floors and illuminated ramparts The largest of these is just 2.4 km in diameter so they are challenging objects but the illumination was just right to make the best of them tonight

I'm really enjoying the levels of performance that my big refractor is now delivering

[lunator]

John

Good report

The refractor is a real cracker

Cheers

Ian

[Doc]

A lovely report John I really enjoyed reading it.

By the sound of it you didn't manage to split the crater in Plato into two seperate craters, that would have given you four. Even in my 16" I could only manage four most of the time so you are doing really well with your 6" refractor.

The rille within the Alpine Valley is pretty hard as well I needed x457 to be able to see it the last time I tried. I think it's very dependant on seeing conditions and good libration. The rille is supposed to be approx 750 metres wide and 130 metres deep.

[John]

A lovely report John I really enjoyed reading it.

By the sound of it you didn't manage to split the crater in Plato into two seperate craters, that would have given you four. Even in my 16" I could only manage four most of the time so you are doing really well with your 6" refractor.

The rille within the Alpine Valley is pretty hard as well I needed x457 to be able to see it the last time I tried. I think it's very dependant on seeing conditions and good libration. The rille is supposed to be approx 750 metres wide and 130 metres deep.

Thanks Mick

You are right - I could only see the craterlet pair as a single last night no matter how hard I tried so I'm only counting it as 3

The rille sounds an even stiffer challenge but it's always worth a shot when the conditions are right. It's a lovely area of the lunar landscape to study anyway so it's hardly a chore

[John]

John

Good report

The refractor is a real cracker

Cheers

Ian

Thanks Ian

The collimation was a little off at SGL5 so, while it did OK on Saturn and DSO's, it ran out off puff on tight doubles pretty quickly then. The cheshire shows almost spot on collimation now