The gray line, or daylight/darkness terminator, is a constantly moving circle around the earth where a daylight/darkness transition is taking place. When this circle is over your QTH, potentially enhanced propagation along the terminator is possible, especially on lower frequencies. The timing and potential for gray line propagation depend on a number of predictable (season of the year) and unpredictable (solar conditions) factors. Gray line QSOs can produce new multipliers and/or memorable contest experiences.
Geochron’s magnificent world mechanical clock (featuring 300 moving parts) and its digital clock for 4K TV display the gray line in real time—a genuine benefit for DX enthusiasts.
