It forms a matching pair with Theon Junior, about two crater diameters to the south-southeast.

[1][2][3] This crater is circular and bowl-shaped, with only a small floor at the center of the steeply sloping interior walls.

The crater appears relatively young, as it shows little sign of wear due to impacts.

[2] Theon Senior is from the Eratosthenian period, which lasted from 3.2 to 1.1 billion years ago.

[2][3] By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Theon Senior.