St. Elmo's fire is a bright blue or violet glow on tall objects when air is full of electricity, often seen during storms by sailors.
St. Elmo's fire is a bright blue or violet glow that appears on tall objects when the air around them is filled with strong electricity. You might see it on the tips of ship masts, church spires, chimneys, the horns of animals, or even on the front edges of airplanes, and you might hear a faint hissing or buzzing.
It happens most often when the sky is full of electric charge, such as during thunderstorms or big volcanic eruptions.
The air near a pointed edge becomes charged and starts to glow; this is ionization, which creates glowing plasma.
It was named after St. Erasmus of Formia, also called St. Elmo, who is the patron saint of sailors.
Ancient writers gave the glow different names, like Helene for a single bright spot and Castor and Pollux when two glows appeared.
In 1899, Nikola Tesla used a high-voltage coil and saw glowing blue rings around the machine and even around butterflies, showing the glow can come from strong electric fields, not magic.