That line on the moon right now...

[ED209]

Gazing idly at the moon I've just noticed a feature of comparative interest (to us anyway! ), and I'm wondering what it is?

It's easy to find right now. Near the terminator about one third up from the bottom (as orientated to the naked eye) there is a quite a big crater almost all the way across the flat bottom of which is a very sharp, very crisp long shadow. From its direction, it look like the shadow of a very long rift or crack that has the side nearest the sun much higher than the other, so that it casts a wide crisp shadow.

But, the rift seems bounded by (and so younger than) the crater. Whatever it is, it was plonked in place as we see it now (i.e it's not a fragment of a bigger larger feature, like a very prominent ray or somesuch).

Does this whatsit have a name, and what do we reckon caused it?

[richbyers]

just been observing the moon, didnt spot anything like that, how much magnification were you using? just so i have an idea of where you are

rich

[kniclander]

it's Rupes Recta -the straight wall - perfect tonight and lovely with Thebit and Birt either side of it.

[ED209]

Thanks - that's definitely it

Looks good at 100x, I think

Rupes Recta is a linear fault, or rille, on the Moon, in the southeastern part of the Mare Nubium at 22°06′S 7°48′W / 22.1°S 7.8°W / -22.1; -7.8. The name is Latin for "Straight Fault", although it is more commonly called the Straight Wall. This is the most well-known escarpment on the Moon, and is a popular target for amateur astronomers.

When the sun illuminates the feature at an oblique angle at about day 8 of the Moon's orbit, the Rupes Recta casts a wide shadow that gives it the appearance of a steep cliff. The fault has a length of 110 km, a typical width of 2–3 km, and a height of 240–300 m. Thus although it appears to be a vertical cliff in the lunar surface, in actuality the grade of the slope is relatively shallow.

Well I never - it's a gentle slope that happens to be lit from a perfect angle, and not a cliff at all. Well, I suppose 1:10 is actually quite a steep slope, not so easy to cycle up...except perhaps on the surface of the moon....

[Talitha]

When it's illuminated from the other side, you'll see a white line instead of a dark shadow (can you tell i'm not an imager? )

[jgs001]

Well spotted... took me ages to find it first go. An interesting difference Carol... never realised the change in colour, not seen it under that illumination...

[ED209]

I've found and installed Virtual Moon Atlas - how awesome is that programme? A zoomable high-res map of the moon with every point of interest labelled, described physically and its history noted

[skywatcher250]

ed209 - thanks for the heads up with moon atlas... exactly what i was looking for !!!!!

[MarkF]

Thanks for the link to VM just what is needed over the next couple of nights.

[marcdearn]

VMA!!!

What a find....thanks very much

[JonH]

I was wondering what that very distinct straight line was too.

Thanks for the info, and now I'm going to check out VMA...