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John

When is a rille not a rille ?

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Over the past hour I've been observing the moon with my 5" refractor - now that it has risen in the sky a bit it's a fantastic sight :)

Copernicus is really well placed tonight, near the terminator and filled with intriguing shadows ....

Just to the north of Copernicus, in the foothills of the Montes Carpatus, I spotted a very thin rille running across the rugged landscape of the region. Having looked it up using the Virtual Moon Atlas I find it's named Rima Gay Lussac and is around 40 km in length and 1 km wide.

References on the WWW referred to this feature as a cantina which is a crater chain rather than a rille. A number of rilles are actually chains of similar sized craters when viewed though really large scopes or from photos taken by lunar probes.

I was pretty pleased to spot this feature - It's labelled as being a challenge for a 12" aperture in the Virtual Moon Atlas so I'm chuffed to have spotted it with my 5" :)

John

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I'd have to question the difficulty rating given by the VMA.. the rille is fairly easy to see with my 8" SCT.

TBH, i've never seen Rima Gay Lussac referred to as a catena. Some rilles have collapse pits in them (like Rima Hyginus) and may 'appear' to be a catena, but they're actually not. Maybe this is where the confusion comes from?

In any case, i'm glad you got some nice lunar views. :)

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I'd have to question the difficulty rating given by the VMA.. the rille is fairly easy to see with my 8" SCT.

TBH, i've never seen Rima Gay Lussac referred to as a catena. Some rilles have collapse pits in them (like Rima Hyginus) and may 'appear' to be a catena, but they're actually not. Maybe this is where the confusion comes from?

In any case, i'm glad you got some nice lunar views. :)

That's interesting Carol - I'll need to do some more reading !.

I agree that VMA's rating is pessimistic - while it was not an "easy" spot in the 5", once found, it was reasonably clear and did not come and go with seeing. With the viewing conditions for lunar features varying hugely depending on the phase I can't really see that there can be too many hard and fast rules on what you can and can't see with given apertures. With some features the "window" of lunar illumination can be very short - even an hour can make a real difference with some features.

John

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I distinctly remember viewing a crater chain and believing it was a rille until I was proved wrong by VMA. Wish I could remember which one it was now....

Nice objects!

Andrew

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Oh, yes - I remember. It's the chain near Stadius and Copernicus. Fantastic object as I remember it.

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