December 18, 2007

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The Pearl Necklace

south up drawing by Phil Morgan

Fra Mauro Is a very old crater. That may be stating the obvious, but it is still one of the most interesting of lunar objects to study,draw or photograph. The sketch shows well an effect that I nicknamed the ‘Pearl Necklace’. This spectacle is produced for only a very short period of time at Sunrise when the early morning rays of sunlight are just catching the individual peaks of the much battered and denuded west (right on this south up view) wall of the old crater. The floor of Fra Mauro is covered in low hills and ridges, and there is a considerable breach in the east wall where presumably lavas flowed in or out in the past, with only a few craterlets, hills (and possibly domes) to mark its remains. On this occasion only the Rima Parry 1 could be made out crossing the floor from south to north, with some of the old floor ridges and hills mimicking its alignment. To the north is the interesting heart shaped plateau that is bisected by a wide valley that terminates at the prominent peak Eta. This mountain has a summit craterlet, but this is not visible until the Sun gets higher in the lunar sky. The eastern part of the plateau is lettered Zeta, and has a much rougher surface than the smoother western section. Although this observation took only 50 minutes, in that time the ‘Pearl Necklace’ had already started to break down, with the individual peaks of the west rampart starting to merge together, showing just how transitory the effect is. I should be interested to know if any one has taken photographs of Fra Mauro at around this colongitude showing this effect.

Phil Morgan

Technical Details
27 March 2007, 19:10 to 20:00 hrs UT. 305 mm f/5 Newtonian x400. Sun’s colongitude 17.58° to 18.00°.
Originally published in the November, 2007 BAA Lunar Section Circular.

Related Links
Rükl Atlas plate 42
Not quite to the Necklace view

Yesterday's LPOD: Wahoo for Wan-Hoo

Tomorrow's LPOD: Polar Correction


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