BEACON, a conspicuous object, either natural or artificial, visible as a mark from a distance by day and, if lighted (e.g., a lighthouse), at night. More particularly it is a fixed mark of dis tinctive construction provided to assist the mariner, by day, in identifying his position and fixing his course, or to indicate the position of hidden dangers. Beacons are essentially fixed marks as distinguished from floating marks, e.g., a marking buoy, although the superstructure usually carried by a marking buoy—such as a globe or cone—is sometimes referred to as its beacon. They are usually constructed of masonry, concrete, iron, steel or timber, size and form varying widely with the circumstances and position. Simple and primitive forms are a cairn of rough stones, and masts of wood or iron surmounted by a cage or other appropriate top mark. In exposed wave-swept positions beacon structures must be strong and securely founded. Usually they are painted in con spicuous and distinctive colouring to increase their visibility and aid their identification by the mariner. They are erected on head lands and other positions on the coast line, small islands, isolated rocks, reefs and shoals, or to mark the limits of the fairway in harbours, estuaries and rivers. In some instances disused build ings in a conspicuous position on the coast, which otherwise might fall into ruin, have been preserved and maintained as day marks or beacons by a lighthouse authority. Beacons marking fairways are fitted with top marks of the conventional form or colour pre scribed by the appropriate lighting or navigation authority in the same way as marking buoys.
A beacon sometimes carries a small light arranged to function automatically and unattended for a considerable period, and thus serves as an aid to navigation at night; such lighted beacons are often employed for fairway marking (see LIGHTHOUSES). Two beacons are sometimes so placed, at a suitable distance apart, to indicate, when seen in line, the direction of a submerged danger, or a line of fairway. If, in addition, they are lighted at night, they are described as "leading" or "direction" lights. (N. G. G.) Beacons in Aviation.—In commercial aviation beacons or aerial lighthouses (see LIGHTHOUSES) are in general use for two purposes : the distinctive marking of airports at night; and (2) for marking established airway routes at night.