What is St. Elmo's Fire?

Saint Elmo (Erasmus of Illyricum) may have become the patron of sailors because he is said to have continued preaching even after a thunderbolt struck the ground beside him.

This prompted sailors, who were in danger from sudden storms and lightning, to claim his prayers.

The electrical discharges at the mastheads of ships were read as a sign of his protection and came to be called "Saint Elmo's Fire".