June 6, 2018
Not Officially Birt R
Originally published February 27, 2009
image by K.C. Pau, Hong Kong
Classical selenographers often designated very ruined large craters with the letter R. When we did the map shows that all the lavas in this area have a similar range of colors, so that isn't the explanation. Here is another possible reason. Since mare ridges tend to form over buried rims (Serpentine Ridge basin ring in Serenitatis and the buried crater rim of R, as examples), perhaps the lack of mare ridges within R is because the excavation of that 200 km wide crater obliterated the existing craters and possible basin rings. While you ponder that, I thick KC may have captured another hairline crease in the maria. A few years ago one of his images brought the rille at top center to our attention. Now I see a fainter and shorter crease in the 7 o'clock position from Birt extending to the southwest rim of R. Near its top this seems to truncate the previously-noticed, similar north-south feature. These creases suggest that more rilles, perhaps originally like the Birt Rille, have been mostly buried under R's last lavas. Hasn't it been useful to have a designation for the ancient ruin that holds the Straight Wall, the Birt Rille and these other rillitos?
Feb. 3, 2009; 13:52 UT. 250mm f/6 Newtonian + DMK31AF03 camera + 2.5X barlow; processing with CS2. Lat.: 22º 15' N, Long.:114º 10' E; elevation is 0 meter.
Rükl plate 54
Rik Hill's image shows an earlier view of the 7 o'clock crease.
By the way, this is the type of very low Sun image that most lunar orbiters never capture!
Yesterday's LPOD: An Unfamiliar Fresh Crater
Tomorrow's LPOD: Looking Inside Rocks