Mare Humboldtianum (Moon)

Named after Humboldt, Alexander von Humboldtianum - German natural historian (1769-1859).

Mare Humboldtianum is a lunar mare located within the Humboldtianum basin, just to the east of Mare Frigoris. It is located along the northeastern limb , and continues on to the far side. Due to its location, the visibility of this feature can be affected by libration, and on occasion it can be hidden from view from Earth. The basin material is of the Nectarian epoch, with the mare material being of the Upper Imbrian epoch. (wikipedia entry)

A mare is a "sea" or large circular plain. On the Moon they are named after latin terms describing weather and other abstract concepts.