Whitepeak Observatory, Tacoma, WA

Changing Faces: Rupes Recta


Here's a graphic I made to illustrate the magnitude of changes in the appearance of Rupes Recta from lunar dawn to dusk. That this feature has, in effect, only one "side" makes for a dramatic appearance change--it's obviously much more plain to see during the lunar morning than the lunar evening.

Another view, closer to the lunar sunset, is provided from this image i took during the Sept. lunation:

This variation shows Rupes Recta even closer to the evening terminator. Rupes Recta shows both as a sun *and* shadow feature. Because of the profile (see first montage) the slope which generates the shadow is shallow and thus this 'upslope' shadow is evident only at such very low sun angles. The 'white line', created by the sun shining brightly on the downslope, is still the most prominent. But note, at this low angle of illumination, even the sunlit slope is not as intensely bright as when the sun hits it at a slightly higher angle! This isn't really too suprising once one realizes that as a reflectance feature a certain range of incidence angles is bound to reflect sunlight more efficiently towards an observer on earth than other, less optimal, angles of incidence.


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