luminosity accompanying brushlike discharges of atmospheric electricity that sometimes appears as a faint light on the extremities of pointed objects such as church towers or the masts of ships during stormy weather, or along electric power lines. It is commonly accompanied by a crackling or hissing noise.

St. Elmo's fire, or corona discharge, is commonly observed on the periphery of propellers and along the wing tips, windshield, and nose of aircraft flying in dry snow, in ice crystals, or near thunderstorms. Various flight procedures, in addition to mechanical and electrical devices designed to reduce the accumulation of electrical charge, are utilized as safeguards in preventing or controlling these discharges.

The name St. Elmo is an Italian corruption, through Sant' Ermo, of St. Erasmus (Erasmus, Saint), the patron saint of Mediterranean sailors, who regarded St. Elmo's fire as the visible sign of his guardianship over them. The phenomenon was considered to be a token of good luck because it is most pronounced near the end of a storm.