image by Christian Arsidi, Vernouillet, France
Reading a lunar scene means recognizing each feature, interpreting its origin and determining its relative age. The oldest feature here is the rough terrain at upper left - from a wider view, it could be a relict of the rim of the Nubium Basin. The Mare Nubium lavas fill the basin, but the ruined crater Wolf T near the bottom right is older than at least the upper layers of lavas; it formed on the floor of the basin or on an earlier lava flow in the basin. A number of other hills and ridges are also probably pieces of post-basin, pre-mare craters. Nearly all of the remaining craters formed after the Nubium lavas were erupted. Bullialdus A (just to the southeast of the crater rim) existed before Bullialdus and has been greatly degraded by its ejecta. Bulliladus itself was the next main feature to form, and there are radial ridges due to its secondary craters and ejecta. Superposed on top of this ejecta is Bullialdus B (south of “A”) and König (bottom left) which formed later. Notice the smooth lava northwest of Bullialdus - it is not covered by ejecta, and in fact, embays the crater’s rim deposits. Thus, Bullialdus formed after most of the Nubium lavas erupted, but some final stage ones followed it. The last and continuing phase of activity is the random formation of small sharp-rimmed impact craters across the entire scene. One final observation - Christian’s great image reveals layering in the upper rim of Bullialdus - see the dark, light, dark, light banding near the top of the southwest rim? These are probably layers in the original mare surface that were bent up during the formation of Bullialdus.
Dec 19, 2007. Celestron 14 ” (355mm) + Titan 50 Losmandy mount + Barlow 2x + DMK 41AF02 camera, with 15 images a second, treatment with Iris.
Yesterday's LPOD: The Coming Lunar Name-Rush
Tomorrow's LPOD: Seasonal Wishes