Named after Of Smyrna Senior - Greek mathematician and astronomer (c. A.D. 130).
Theon Senior is a lunar impact crater that is located to the northwest of the crater Delambre, and south of D'Arrest. It forms a matching pair with Theon Junior, about two crater diameters to the south-southeast. The satellite crater Theon Senior A can be found to the north. Theon Senior is named for Theon of Smyrna, a 1st-century Greek mathematician and philosopher. (wikipedia entry)
A crater is a circular depression likely created by an impact event. On the Moon they are named after deceased scientists, polar explorers, astronauts or cosmonauts.
