Nansen is an old lunar impact crater along the northern limb of the Moon, on the eastern side of the north pole.

When brought into view during a favorable libration, this formation can be located by finding the crater Baillaud, then following the surface up towards the limb.

This formation has been heavily worn and eroded by minor impacts, leaving an irregular outer wall that is marked by multiple small craters and indentations.

A small crater lies across the northern rim of Nansen, and a similar formation is located along the inner southern wall.

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Nansen.