Alpine Valley Rille ✅

[Captain Scarlet]

I briefly mentioned last night in the “What did you see” thread that I’d finally observed the Alpine Valley Rille, after years of trying. I recall the first time it was brought to my attention. I’d only recently got into observing, probably around 2018/9, and I’d been invited along to a Walton Astro Group. I think I had just acquired my LZOS 105. We were viewing the Moon and @Stu was looking through his Tak saying he could see the Rille, could I? I remember being confused about what and where the Alpine Valley was. Ever since I’ve tried to see it, perhaps 20-30 times, without joy.

Last night I got it, in slightly frustrating circumstances. I saw it for only 20-30 seconds before clouds came.

i thought I’d post about it in more detail here to describe exactly what I was seeing, and to speculate on why last night but never before.

I’d noticed on the Moon Maps app that the Valley was right on the Terminator and that the sky was clear. I’d taken out my SVX140T and the AZ-EQ6. As I was aligning I saw that the seeing seemed really good. Herring-bone clouds were approaching so I had not much time.

i headed straight to the moon starting at 72x (DeLite 13) and everything was really sharp and still. I put in the Delos 6 (156x) but it wasn’t enough magnification to tell if there was anything “down the middle” of the Valley, though it looked promising. In went the Delos 4.5 (208x) and yes there was definitely a feature “between the walls”.

The Valley walls were extremely bright one side and dark the other, with a fainter line down the middle also well-illuminated. One tall feature was casting a shadow all the way across. It was the brightness of the rille-edge that allowed it to stand out: there was no doubt. It’s far easier to notice bright-against-darker than the other way around.

Unfortunately, I was seeing now through fortuitous gaps in the cloud, and as I swapped in my Delos 3.5, I realized there were going to be no more gaps. Dammit, the seeing would’ve allowed a lot more magnification.

The rille is, I understand from reading around, generally very difficult to observe. I think the combination of excellent seeing, the Alpine Valley being dead on the Terminator and high quality optics were all necessary for me to eventually crack the nut. I’m pleased.

Cheers, Magnus

[John]

Great report and result Magnus 🙂

So far, I've only managed to see that rille with a 12 inch dobsonian. I think the illumination of that area of the surface is critical to being able to discern this very fine feature. That, good seeing, optics and a keen eye 🙂

Well done !

[MalcolmM]

Great report, and it provides me motivation to keep trying! I was looking last night in pretty good seeing with a Mewlon 180C but despite seeing the dark and light walls of the valley, I could not see the rille. In my limited experience, the correct angle of illumination is critical for these sort of features. I'm hoping with just the right illumination, the 180C is good enough to resolve the rille. I'll certainly keep trying. 

Malcolm 

[astro_al]

Well done Magnus!

I tried the night before last with no luck. I think I was a day early and unfortunately last night was cloudy.

Thanks for the report though, encourages me to keep trying.

Al