Dome-1, AS16-1411
"Webbing" shown in red
This JPEG image is from a photograph taken by the Apollo 16 mapping camera, AS16-1411. It shows the same structure that was labeled Dome-1 in the Lunar Orbiter 4 image. This Apollo photograph was an oblique view of the Moesting A region. The camera's line of sight was elevated only 30 degrees above the local horizontal, as opposed to the nearly-orthogonal view of the object in the Lunar Orbiter photograph. To compensate for the difference in viewing angle, the Y-axis of this JPEG image was increased by a factor of 2 to produce an orthogonal projection, comparable to the Lunar Orbiter image. No other enhancements were done to the image.
The unenhanced JPEG of this region has not been reaspected, so it shows how the region looks from the oblique perspective of the Apollo.
The dome in AS16-1411 is 70 times the width of the theoretical resolution of the Apollo mapping camera, which would be almost 3 times better than the resolution of the LO4 image. However, the resolution was specified at a contrast ratio of 1000:1 for the Apollo cameras whereas the Lunar Orbiter camera resolution was stated for a contrast ratio of 3:1. The effective resolution of the Apollo image may actually be less than the resolution in the Orbiter photograph, judging by comparison of the two images themselves. While the resolution may not be as good, this Apollo image does provide some additional information about the object due to the difference in lighting geometry. The elevation of the sun was 15 degrees here, 3 degrees lower than in the LO image. The camera-target-sun angle is also very different from the LO image. As a consequence, the surrounding plains are darker and are in higher contrast to the object, making its shape more apparent.
While the cellular pattern on the object's surface in the Orbiter image is not as apparent here, the surface does have a mottled appearance differing from that of the surrounding hills. On both of the "arms" extending south (toward the bottom of the image) from the object, evidence of cross-hatching is visible near where they join the dome at the inside corners. The pattern in the LO image also appeared to extend from the dome out onto these "arms," although it is clearer in the Apollo image. There is a curved "rib" visible running from lower right to upper left over the surface of the dome.
Dark patches with linear boundaries, most clearly visible on the left side of the structure, may be the same cellular pattern observed by Lunar Orbiter 4 in the same area of the object's surface. The pattern of light "webbing" of which these dark patches appear to be a part, is traced out in the insert on the right below.
Dome-1, AS16-1411
"Webbing" shown in red
The puzzling triangular shadow can also be seen to cross the southern part of the dome, with one apex ending on the hill to the west. The 3-degree difference in sun angle between this photograph and the Orbiter photo should cause this shadow to be about 25% longer, but it does not seem to have changed shape relative to its appearance in LO4-108H3. This suggests that it is not really a shadow. It might be either a highly regular patch of low-albedo material on the surface, or a translucent panel suspended a few hundred feet above the surface. The former explanation leaves almost as many open questions as the latter; what would cause such a regularly-shaped patch of dark material, and why would it cover several very different kinds of terrain?
A16Dome.jpg - Image area is 0.83 degrees wide, 0.40 degrees vertically (image stretched by a factor of 2 vertically)
A11raw.jpg - Image area is 1.29 degrees wide, 0.80 degrees vertically.
Spacecraft Altitude = 114km
Principal Point in Photograph = 6.1 degrees South, 5.6 degrees West
Sun Elevation at Principal Point = 15 degrees