Planck is Ridge Section 158 and named after the huge, 314 km-wide, lunar crater that is located in the southern hemisphere on the lunar Far Side. It lies to the west of the walled plain Poincare (Ridge Section 159), another enormous formation only slightly larger than Planck. Both formations are larger than the walled plain Bailly, the largest crater on the NEAR side. Lying across the southeast rim of Planck is the crater Prandtl. Like many lunar formations of this size, the outer rim has been damaged and eroded by lesser impacts, leaving a rugged ring of peaks and ridges that is notched and incised by small craters. The western rim of this walled plain is neatly overlain by a long lunar valley designated the Vallis Planck. Despite its name, however, this valley is actually radial to the walled plain Schroedinger (Ridge Section 159) to the south. The valley is about 451 kilometers in length. The most notable feature on the interior floor of Planck is a multi-crater formation in the northern half consisting of Planck W, Planck Y, Planck Z, Planck B, and Planck A. The interior of Planck Y has been almost completely flooded by lava, leaving only a shallow perimeter. Likewise Planck Z has been flooded, although its rim is somewhat more prominent. The interior of Planck B is partly occupied by a concentric crater, and the floor contains several clefts. Parts of the remaining floor of Planck are level and smooth, at least in comparison with the surrounding terrain. This is particularly so in an arc along the northern inner wall. The southern half of the crater is somewhat more irregular, although still forming level plains in places. There are many small craters across the interior of Planck, and a few ghost crater remnants. (Credit: Most of the information used in the section feature descriptions was obtained from wikipedia.org. Section 158 and this directory was created by Fran Ridge and Ned Haskin of The Lunascan Project).