Apianus is a lunar impact crater that is located on the rugged south-central highlands of the Moon. It is named after 16th century German mathematician and astronomer Petrus Apianus.^[1][2] It is located to the northeast of the crater Aliacensis, and to the northwest of Poisson. The worn crater Krusenstern is attached to the west-northwestern rim.

The outer wall of the crater has been worn and eroded by subsequent impacts, and a pair of small craterlets overlay the rim to the southeast and northeast. The central crater is 63 kilometers in diameter and 2,080 meters deep.^[1] The craterlet on the southeast rim, Apianus B, is a member of a cluster of co-joined craterlets that includes Apianus T and Apianus U. The interior floor of the central crater is relatively smooth and lacks a central peak, although the surface appears somewhat convex. Only a few tiny craterlets mark the surface.^[3]

The crater is from the Nectarian period, 3.92 to 3.85 billion years ago.^[1]

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Apianus.^[4]

• 19139 Apian, asteroid