LPOD June 18, 2008
image by Stephen Sharpley, Melbourne, Australia
Another LPOD springs from a submission to the LPOD Photo Gallery! This one is interesting because of the mare ridges behind the multidome Rümker. None of the ridges have names, and their origins have been speculated about but are uncertain. Many mare ridges are concentric to the rims of the impact basins that contain them and the mare lavas they form in. Such ridges are interpreted as the surface expression of low angle faults that occur as the mare's weight causes the basin center to sag, forcing the lava into a smaller radius container. The northern Procellarum ridges do parallel the edge of the nearby shoreline, and, in fact, Ewen Whitaker proposed that the ridges help define a middle ring of the 3200 km diameter Gargantuan Basin. Under this interpretation the three parallel ridges are analogous to the inner ring of ridges that passes south of Sinus Iridum and the Spitzbergen Mountains in the Imbrium Basin. The ridges just north of Rümker and some of the smaller ones at odd angles may not be related to the big three, so there are still plenty of features to investigate. And of course, many lunar scientists doubt that Gargantuan exists so other explanations may be needed for the all the ridges.
06/16/08 14:22 UT. Mewlon 250 + DMK 31AF03.AS + Astronomik G filter
Rükl plate 8
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1. I don't know whether or not it's possible, but I think it would be useful to have a kilometer/mile scale of some kind featured just below the right-hand corner of the images. Not on the image, but just below it.
2. Bill - its possible and would be useful but I don't have time to do it every night. I do need to more consistently add in the text a diameter for a feature - for example Rümker is about 70 ikm n diameter.
3. Chuck- I didn't mean my comment as a criticism. It was just wishful "thinking out loud." I can only imagine how busy you must be with your work on the Cassini project, and other professional responsibilities. It's too bad you don't have an assistant with the professional and technical skills necessary to help with the LPODs. That might help lighten the load. (??)
4. Interesting unofficial name! Gargantuan Basin.
-- Danny C.
5. Chuck- It’s certainly true that the naming of lunar ridges is haphazard, but it’s not quite true that none of the ridges in Stephen’s image have official names. The little fragment of shadow-casting land in the extreme lower left is a piece of Montes Agricola, and the ridge that enters the frame just above it is the northern extreme of Dorsa Burnet. The ridges that feed out of Montes Agricola just below Dorsa Burnet, merging into a snaky line running parallel to, but below it are Dorsa Whiston, and the ridge that starts above Dorsa Whiston and runs tangent to one of a pair of similarly-sized small craters (Lichtenberg B and Naumann G) is Dorsum Scilla. You can see more precise identifications on maps LAC 23 (604 kb PDF) and LAC 38 (540 kb PDF) of the USGS Digital Atlas. The reason the ridge-naming stops a little south of Naumann is that nearly every official lunar ridge name was assigned on an Apollo LTO chart, and the northern limit of the charted zone in this area is near Humason. In fact, Dorsum Scilla barely got a name, since only 14 km of its southernmost tip (on the left in the LPOD image) seems to have been photographed by the Apollo Metric cameras.
Bill- Specifying a kilometer scale is not always easy, especially for images like Stephen’s where the foreshortening seen from Earth causes the scale to be quite different in different directions. If you have access to a Windows PC, I’ve placed calibration data for today’s LPOD in the LPOD Notes section of the LTVT Wiki (this is possible whenever the date, time and observing location for the LPOD image are given). Following the directions provided there you can load today’s image into the freeware LTVT software for viewing and analysis, including automatically identifying all the IAU-named features. In particular, if you right-click on the displayed image you can set the “Reference” point anywhere you wish and readout the distance in kilometers from that point to any other on Stephen’s image. For example, you can right-click on the lower left corner, then move the mouse to the lower right to find the exact distance along that edge (577 km). Likewise you can set the Reference Point at the left-hand end of Dorsa Scilla and measure how long it would be if it extended to Naumann G (114 km -- close to its official IAU "diameter" of 108 km might), or to Naumann (164 km, as the USGS Nomenclature map #23 seems to indicate), or far beyond that (244 km, or more, as Stephen’s photo seems to show). By changing the mouse options you can also use LTVT to estimate how tall Dorsum Scilla is (it seems to be about 300 m on the shadow-casting side; and the other ridges seem mostly to be in the range 300-500 m).
For the benefit of those unable to enjoy the interactive labeling capabilities of LTVT, I’ve also posted at the same site an automatically-labeled version of today’s image, although this is probably redundant with Jennifer Blue’s beautiful nomenclature maps.
- Jim Mosher
5. Jim--Thanks for your suggestions. I'll take a look at the LTVT software, etc. that you mention. I think I looked at it once before and was a bit intimidated by its navigation requirements. As an amateur, I may not have the technical skills required to use LTVT properly. I'll try it, though. It certainly looks very useful.
6. Bill - No criticism taken - I agree, but don't have the time or the assistant.
Danny - Also Procellarum Basin is an unofficial name. And don't forget Kepler's name for the farside: Privolva.
Jim - Thanks for always keepng me honest, after the fact! Its very useful to see the LPOD with the overlays.