What term refers to the greatest distance that can be seen throughout at least half the horizon circle?

The correct term for the greatest distance that can be seen throughout at least half the horizon circle is prevailing visibility. This measurement is crucial for pilots and air traffic controllers because it helps determine the conditions for safe flight operations. Prevailing visibility is defined as the greatest distance that objects can be seen and identified, which is typically measured in statute miles or meters and considers the visibility across a significant portion of the horizon.

Understanding this distinction is essential for various aviation processes, such as takeoff and landing, where visibility impacts decision-making. Other terms might refer to visibility conditions in different contexts, but prevailing visibility specifically addresses the distance that can be seen across the half-circle of the horizon, reaffirming its importance in assessing flight safety and operational capabilities.