What is the circle(maybe ambient occlusion) that is around any camera main camera and editor camera and how to adjust it

When I walk in my game the objects in the distance from my camera are shaded/look different and as I get closer they appear in full detail, but when i am in the sky they appear full detail. this all happens at the same time in a circle(maybe ambient occlusion) around the camera, renders stuff close by in full detail and the farther stuff in not good detail. So my question is how do I adjust the distance so that stuff farther away get rendered or show up in full detail?