The surface of the Moon looks very different in orbiter images taken at local noon than it does in images from other times. Here are two examples of the same places in Lalande Crater. In each image, the top section was taken near local sunset (sun incidence angle 68o) and the bottom section taken near local noon (sun incidence angle 12o):

fresh impact crater in central peak of Lalande Crater

The above are images M1096551351LC and M1103624254LC (which is flipped horizontally in the online display). The crater shown is about 80 m across. Coordinates about 4.47oS by 8.6oW.

large chunks of debris on south rim of Lalande Crater

The above are images M1154271821RC (which is upside down in the online display), and again M1103624254LC. The white boulder debris field is about 120 m across. It is at coordinates about 4.85oS by 8.6oW.

All of these images were taken with the narrow-angle camera of the Lunar Reconnaissance Orbiter, so they are of the visible-light spectrum only (but recorded in black and white). I have been trying to understand how the big changes in apparent tone work. This blog post from the Moon Zoo project says that fresh impacts and their ejecta are bright because

their newly exposed and broken surfaces are clean and shiny and have a relatively high albedo in comparison to the mature, darker mare material they lie on top of

Does this basically mean that particle surfaces are smoother at the microscopic level? Is there a chemical difference too? I have read about the Opposition Effect, but that doesn't seem relevant. And none of this explains the black stuff - what is that?

Here are a couple of other images of the area, the first also from the LRO, showing normalized surface temperature variations, and the second from Clementine, showing optical maturity, imaged in the UV spectrum.

Average surface temperature from Diviner instrument Optical maturity from Clementine

  • $\begingroup$ It's interesting to compare the NAC pairs to the images. There are noticeable differences, but they aren't quite as pronounced. $\endgroup$ – PearsonArtPhoto Sep 7 '15 at 21:32
  • $\begingroup$ @PearsonArtPhoto do you mean the C and E versions? I have thought about asking about those pairs in a separate question. I haven't found an explanation of what the difference is. There isn't any reference to there being any filters on the NAC. I did slightly sharpen the top of the first image, otherwise the colors haven't been touched. And i stretched the bottom of the second image to get it to the same scale. $\endgroup$ – kim holder Sep 7 '15 at 22:05
  • $\begingroup$ What are the exposure times on these images? $\endgroup$ – called2voyage Sep 8 '15 at 19:10
  • $\begingroup$ @called2voyage the orbiter scans the ground as it moves, so the exposure time here applies to each line of the image. The frame taken close to local noon that appears in both examples lists a line exposure duration of 0.00051 s. The one taken near sunset in the top one has a line exposure time of 0.00069 s. The one from near sunset in the bottom one was 0.00068. $\endgroup$ – kim holder Sep 8 '15 at 21:02
  • 1
    $\begingroup$ @kimholder I wonder if the darker spots have a greater presence of the iron spherules mentioned here on page 1668. At sunset there is low contrast between highly reflective regions and highly absorptive regions, but at noon the reflective regions shine brightly and the absorptive regions contrast darkly with the rest of the regolith. $\endgroup$ – called2voyage Sep 9 '15 at 14:52

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