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Snail on Luna!

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1 year 3 weeks ago #111791 by flt158
Snail on Luna! was created by flt158
Hello everyone. 

I had my William Optics 158mm f/7 apochromatic refractor in my back garden on Sunday night 26th March 2023. The clouds were breaking up; and by the time the sky was truly dark from 8.30pm, I observed some lovely features on Luna. There was very little wind and I had no hassle with dew. The air temperature got cooler over time – from 6˚ to 4˚ Celsius. I only used 2 eyepieces: my 28mm 2” 40x and my Pentax 10mm 112x eyepieces. The magnitude -9.0 Moon was precisely 5 days old. Its distance was 387,268 kilometres from Earth. Its crescent illumination was 28%, and the angular diameter was 31 arc minutes. 

Immediately I was struck by clair-obscure feature. It involves the large 124km crater Fracastorius which is located in the southern part of Mare Nectaris. The western rim of this crater was completely illuminated by the Sun. It looked like a large snail; and the 28km Fracastorius D very much looked like the shell on the back of the snail.  
There is no need to use a high power eyepiece for this clair-obscure feature. Even less than 30x should be sufficient. Indeed, I found 40x gave a better view than 112x. 
I had Darren on the phone and he observed the "Snail" at 39x with his 10" Dobsonian. 

Three other features I must mention, the first is the 88km crater Piccolomini. Its centre was in darkness. But both its rim and a small amount of its central peak were fully illuminated. Nice!
The second was a rille I have never observed before: Rimae Janssen. I definitely saw one of its main rilles at 112x. It was positioned right on the lunar terminator. Thirdly and finally, I could see the first 20 kilometres or so of Rupes Altai right next to Piccolomini.   

You could say I had a remarkable night with Luna. 

Clear skies from Aubrey. 
The following user(s) said Thank You: michael_murphy, Fermidox, Until_then-Goodnight!

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1 year 2 weeks ago #111796 by Until_then-Goodnight!
Replied by Until_then-Goodnight! on topic Snail on Luna!
More snail related astronomy - things were certainly a bit sluggish in March : ).

Seriously though, that was an interesting clair-obsure effect - thanks for the notification Aubrey.

Clear skies,

Darren.
The following user(s) said Thank You: flt158

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