COMPARISON WITH LUNAR ORBITER 4 IMAGE-ORIENTED TO MATCH IMAGES BELOW
CORRESPONDENCE WITH DR.COOK:
Regarding my two theories, I enclose a further image enhancement - I have arrowed some other areas which might be showing flaring. Usually flaring is just linear, but can be in more than two directions at once (depending upon circumstances in our atmosphere). I am not quite sure what would cause curved flaring, but I saw it the other night on Piton and a few other point-like features. However I am not entirely convinced that the flaring explanation is the answer as I did not find enough examples elsewhere in your image. Only you can tell me for sure by examining your video tape for similar effects on other bright point-like peaks coming out of shadow. The twin valley on the E-rim of Tycho theory I favor more now that I have made a contrast enhancement of your image of the shadow filled floor of tycho. I can see possible evidence for umbra (0% sun) and penumbral (1, 2, ...5, ...10, ... 100% Sun) parts of the shadow and/or possible illumination of the shadow interior. Anyway either or both theories could be wrong and maybe it is a LTP - so I await a more detailed check of your video tape.
FURTHER CORRESPONDENCE WITH Dr.COOK:
Please find enclosed a colorized digital elevation model DEM of Tycho( IMAGE NOT AVAILABLE ) - the original came from Jean-Luc Margot who produced a radar interferometer map of the area with ~100m resolution using Arecibo. I have added some colour - this goes through the colours of the spectrum from violet low, to red high (see floor), and then recycles again for the rim detail. I cannot tell you what the colours mean in real height, but just think of it as relative so you know what is higher than what on the floor or on the rim. OK I've marked in the Sun azimuth and altitude at the time of Brendan's image (see ALPO/BAA web page I mentioned earlier) in which the central peak of Tycho is barely just visible. Also I have Robert's Az and Alt (about 1 deg higher in altitude). Now the DEM shows that there is a gap in the E rim through which the peak might get illuminated early by a fraction of the solar disk. However it does not show to me convincing evidence for the dual valley idea I mentioned in last email. So Robert, please check your video tape for evidence of atmospheric flaring. BTW the height of the highest of the crater floor peaks is ~2.5km above the floor and the rim is ~5-6 km above the floor. Tony -- Dr Anthony C. Cook School of Computer Science and IT, University of Nottingham, Nottingham. NG8 1BB. UNITED KINGDOM