Geological Chronicle
Humboldt is a large lunar impact crater near the eastern limb of the Moon, with a diameter of 199.46 kilometers. British astronomer T. W. Webb noted it as "one of several huge rings on the limb." Due to foreshortening, the formation has an extremely oblong appearance, although its actual shape is an irregular circle. The crater's rim is low, worn, and irregular in outline, with a significant indentation along the southeastern rim where the prominent crater Barnard intrudes. Satellite crater Humboldt B sits south of Humboldt on the west rim of Barnard, while the large crater Hecataeus lies to the north-northwest and Phillips attaches to the western rim.
On the lunar geologic timescale, Humboldt is one of the largest craters of Upper (Late) Imbrian age. The crater floor contains a network of rilles forming a pattern of radial spokes and concentric arcs, making Humboldt a floor-fractured crater. These arcuate fractures provide evidence of forces that worked on the lunar surface to change lunar topography. A central peak forms a range on the floor, where the infrared spectrum of pure crystalline plagioclase has been identified. Humboldt N is the largest crater within Humboldt itself, located north of the central peak, and dark patches lie near the walls to the northeast, northwest, and southeast.
Extending from the crater rim to a distance almost as long as Humboldt is wide, Catena Humboldt is a crater chain approximately 162 km long that passes between the craters Gibbs and Schorr. Due to the crater's location near the lunar limb, little detail was known about Humboldt until it was photographed by orbiting spacecraft, mainly Lunar Orbiter 4. The Apollo 12 mission obtained many photographs of Humboldt in 1969, in which the central peaks appear white because of the high-Sun elevation angle, and Apollo 15 obtained many more photographs in 1971. The crater was named by the IAU after German philologist Wilhelm von Humboldt, and the IAU named Catena Humboldt in 1976.