Jansky is a lunar impact crater that lies along the eastern limb. It lies due east of the larger walled plain Neper, along the southern edge of the Mare Marginis. Due to its location, this crater is viewed from the side from Earth, limiting the amount of detail that can be observed. The visibility is also affected by libration, which can completely conceal this formation from view. (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.