Plain-language answer: Great-circle propagation follows the shortest route over Earth’s spherical surface between two points when the path is otherwise undisturbed.
Why operators care
It establishes a starting bearing, but ionospheric tilt, scattering, aurora, multipath, and long-path propagation can shift apparent arrival direction.
What to compare on air
Calculate bearings from accurate locations, then peak the real signal rather than locking the antenna to the map value.
The common mistake
Treating a great-circle bearing as proof of the actual propagation mechanism.
Forecast boundary
Space-weather indices and propagation models describe probabilities and regional conditions. A usable contact still depends on the exact path, time, frequency, antenna pattern, noise, power, and current observations.
